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Imaging of the Urinary System

The renal system is composed of 2 kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy, 2 ureters Ureters One of a pair of thick-walled tubes that transports urine from the kidney pelvis to the urinary bladder. Urinary Tract: Anatomy, a bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess, and a urethra Urethra A tube that transports urine from the urinary bladder to the outside of the body in both the sexes. It also has a reproductive function in the male by providing a passage for sperm. Urinary Tract: Anatomy. These structures function to filter blood and excrete urine Urine Liquid by-product of excretion produced in the kidneys, temporarily stored in the bladder until discharge through the urethra. Bowen Disease and Erythroplasia of Queyrat, which contains waste products of metabolism. Varying conditions such as infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease, cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change, solid masses, ischemia Ischemia A hypoperfusion of the blood through an organ or tissue caused by a pathologic constriction or obstruction of its blood vessels, or an absence of blood circulation. Ischemic Cell Damage, and mechanical obstruction Mechanical Obstruction Any impairment, arrest, or reversal of the normal flow of intestinal contents toward the anal canal. Imaging of the Intestines can affect Affect The feeling-tone accompaniment of an idea or mental representation. It is the most direct psychic derivative of instinct and the psychic representative of the various bodily changes by means of which instincts manifest themselves. Psychiatric Assessment the renal system. Evaluation of diseases rely on imaging methods such as radiography, ultrasonography, CT, and MRI. Some of these are also used to guide tissue sampling (e.g., renal biopsy Biopsy Removal and pathologic examination of specimens from the living body. Ewing Sarcoma).

Last updated: Mar 14, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Introduction

Imaging methods

The common radiologic methods in use to evaluate the urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract: Anatomy are:

  • Radiography: kidney, ureters Ureters One of a pair of thick-walled tubes that transports urine from the kidney pelvis to the urinary bladder. Urinary Tract: Anatomy, and bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess
  • Ultrasonography
  • CT
  • MRI

Preparation and orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment

  • Prior to interpretation of any image, the physician should take certain preparatory steps. The same systematic approach should be followed every time.
    • Confirm name, date, and time on all images.
    • Obtain information on the individual’s medical history and physical examination.
    • Confirm appropriate exam and technique for desired pathology.
    • Compare any available images of the same area taken using the same method.
  • Determine orientation Orientation Awareness of oneself in relation to time, place and person. Psychiatric Assessment of image:
    • Right or left marker on X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests
    • In the United States, standard exam views place a marker (dot) to patient’s right.
    • For CT/MRI: On axial Axial Computed Tomography (CT) view, the image is sliced and viewed from inferior to superior (as if you are looking from an individual’s feet up)

Radiography

Overview

  • Medical indications: 
    • Obtain a quick overview of the urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract: Anatomy
      • Kidney: renal outlines may be seen, spanning 3–4 lumbar vertebrae Lumbar vertebrae Vertebrae in the region of the lower back below the thoracic vertebrae and above the sacral vertebrae. Vertebral Column: Anatomy
      • Ureter: not visible, but stones can be detected
      • Bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess: if distended, may be seen
    • Examines the main areas “gas, mass Mass Three-dimensional lesion that occupies a space within the breast Imaging of the Breast, bones, stones”:
      • Detects free air in the abdomen
      • On rare occasions, gas, as noted in emphysematous pyelonephritis Pyelonephritis Pyelonephritis is infection affecting the renal pelvis and the renal parenchyma. This condition arises mostly as a complication of bladder infection that ascends to the upper urinary tract. Pyelonephritis can be acute or chronic (which results from persistent or chronic infections). Typical acute symptoms are flank pain, fever, and nausea with vomiting. T Pyelonephritis and Perinephric Abscess, is seen as a mottled collection of air in the kidney.
      • Rarely, soft-tissue masses may be seen.
      • Bone lesions Bone Lesions Multiple Myeloma (sclerotic changes or lytic lesions Lytic lesions Multiple Myeloma) can be visualized.
      • Detects radiopaque Radiopaque An object of high density that blocks X-rays (looks white) X-rays calculi, but only 40%–60% of stones are detected radiographically.
  • Advantages:
    • Low cost 
    • Low radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma dose 
    • Ubiquitous availability
    • Fast
  • Disadvantages:
    • Poor resolution of soft tissue Soft Tissue Soft Tissue Abscess
    • Exposure Exposure ABCDE Assessment to ionizing radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma
    • Individual must hold still for image

Exam technique

  • Positioning:
    • Rotation Rotation Motion of an object in which either one or more points on a line are fixed. It is also the motion of a particle about a fixed point. X-rays:
      • There should be no rotation Rotation Motion of an object in which either one or more points on a line are fixed. It is also the motion of a particle about a fixed point. X-rays.
      • Pedicles of the spine Spine The human spine, or vertebral column, is the most important anatomical and functional axis of the human body. It consists of 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebrae and is limited cranially by the skull and caudally by the sacrum. Vertebral Column: Anatomy should be symmetric. 
    • Visualization:
  • Positioning for specific views:
    • Anteroposterior (AP):
      • Board is against the back. 
      • X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests beams anterior → posterior direction through the individual
      • Can be completed supine or upright
      • Upright is better for evaluating bowel obstruction Bowel obstruction Any impairment, arrest, or reversal of the normal flow of intestinal contents toward the anal canal. Ascaris/Ascariasis and free air.
    • Lateral decubitus (from side while laying down): 
      • Individual is supine.
      • Board is against side.
      • Usually left side down on table (allows better visualization of free air).
  • Penetration Penetration X-rays: degree to which radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma has passed through body, resulting in darker or lighter image
    • Underpenetration: Film appears whiter and features are less apparent.
    • Overpenetration: Film appears darker and features are less apparent.

Interpretation and evaluation

As the obtained image contains multiple organs and structures (and not just the urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract: Anatomy), an inside-out approach Inside-Out Approach Imaging of the Lungs and Pleura (central to peripheral) is taken to provide interpretation:

  • Look at bowel gas Bowel Gas Imaging of the Intestines pattern.
  • Look for solid organ silhouettes ( liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy, spleen Spleen The spleen is the largest lymphoid organ in the body, located in the LUQ of the abdomen, superior to the left kidney and posterior to the stomach at the level of the 9th-11th ribs just below the diaphragm. The spleen is highly vascular and acts as an important blood filter, cleansing the blood of pathogens and damaged erythrocytes. Spleen: Anatomy, kidney).
  • Look for normal fat planes peripherally.
  • Look for evidence of free intraperitoneal Intraperitoneal Peritoneum: Anatomy air.
  • Evaluate soft tissues for abnormal calcifications (stones, masses).
  • Look at the lung bases Bases Usually a hydroxide of lithium, sodium, potassium, rubidium or cesium, but also the carbonates of these metals, ammonia, and the amines. Acid-Base Balance for evidence of consolidation Consolidation Pulmonary Function Tests, effusion, and pneumothoraces.
  • Evaluate osseous structures ( vertebral body Vertebral body Main portion of the vertebra which bears majority of the weight. Vertebral Column: Anatomy height, iliac bones, femurs).
  • Once abnormality is noted, use pattern approach to come up with differential diagnoses.

Normal findings

AP view:

  • Bowel gas Bowel Gas Imaging of the Intestines:
    • Should be present in the small and large bowel
    • Should not distend the small bowel Small bowel The small intestine is the longest part of the GI tract, extending from the pyloric orifice of the stomach to the ileocecal junction. The small intestine is the major organ responsible for chemical digestion and absorption of nutrients. It is divided into 3 segments: the duodenum, the jejunum, and the ileum. Small Intestine: Anatomy > 3 cm
    • Should be uniform throughout the abdomen
  • Organs:
    • Liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy is visible under the right hemidiaphragm; should be uniform with no free air.
    • Stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach: Anatomy and colon Colon The large intestines constitute the last portion of the digestive system. The large intestine consists of the cecum, appendix, colon (with ascending, transverse, descending, and sigmoid segments), rectum, and anal canal. The primary function of the colon is to remove water and compact the stool prior to expulsion from the body via the rectum and anal canal. Colon, Cecum, and Appendix: Anatomy are visible with air in lumen under the left hemidiaphragm. 
    • Renal outlines, if visible, should be in the RUQ and LUQ.
  • Fat planes: normal peripheral fat planes
  • Lung bases Bases Usually a hydroxide of lithium, sodium, potassium, rubidium or cesium, but also the carbonates of these metals, ammonia, and the amines. Acid-Base Balance
    • Should be clear, with minimal lung markings
    • Costophrenic angles should be sharp.
  • Bones:
    • Pedicles should be present and symmetric bilaterally.
    • Vertebral body Vertebral body Main portion of the vertebra which bears majority of the weight. Vertebral Column: Anatomy heights should be gradually enlarging as they move inferiorly.
    • Spinous processes midline
Kidneys, ureters, bladder x-ray showing no abnormalities

Kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy, ureters Ureters One of a pair of thick-walled tubes that transports urine from the kidney pelvis to the urinary bladder. Urinary Tract: Anatomy, bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests showing no abnormalities

Image: “The kidney-ureter-bladder X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests: no abnormal findings.” by Michalakis K, Moutzouris DA. License: CC BY 3.0

Ultrasonography

Overview

  • Medical indications:
    • Emergency care:
      • Trauma with concern for renal injury
      • Concern for urinary obstruction (e.g., calculi/stone)
    • Routine care:
      • Signs and symptoms of renal failure Renal failure Conditions in which the kidneys perform below the normal level in the ability to remove wastes, concentrate urine, and maintain electrolyte balance; blood pressure; and calcium metabolism. Renal insufficiency can be classified by the degree of kidney damage (as measured by the level of proteinuria) and reduction in glomerular filtration rate. Crush Syndrome/ CKD CKD Chronic kidney disease (CKD) is kidney impairment that lasts for ≥ 3 months, implying that it is irreversible. Hypertension and diabetes are the most common causes; however, there are a multitude of other etiologies. In the early to moderate stages, CKD is usually asymptomatic and is primarily diagnosed by laboratory abnormalities. Chronic Kidney Disease
      • Screening Screening Preoperative Care for patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with known renal calculi
      • Screening Screening Preoperative Care for neonates with abnormalities noted on prenatal ultrasonography
    • Monitoring: known congenital Congenital Chorioretinitis disease with predisposition for renal cell carcinoma Renal cell carcinoma Renal cell carcinoma (RCC) is a tumor that arises from the lining of the renal tubular system within the renal cortex. Renal cell carcinoma is responsible for 80%-85% of all primary renal neoplasms. Most RCCs arise sporadically, but smoking, hypertension, and obesity are linked to its development. Renal Cell Carcinoma 
  • Advantages:
    • Low cost 
    • No radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma dose 
    • Widespread availability
    • Fast
  • Disadvantages:
    • Poor resolution 
    • Narrow field of view
    • Individual must hold still for image
    • Technician-dependent

Exam technique

  • Positioning:
    • Individual:
      • Access to the bilateral abdomen
      • Maximize contact between individual’s skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions and ultrasound probe Probe A device placed on the patient’s body to visualize a target Ultrasound (Sonography)
    • Visualization: The kidney should be most superficial to the probe Probe A device placed on the patient’s body to visualize a target Ultrasound (Sonography) without other organs/bowel between the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy and ultrasound probe Probe A device placed on the patient’s body to visualize a target Ultrasound (Sonography).
  • Depth and gain: 
    • Determine the field of view and echogenicity characteristics of the tissue
      • Ideally, the entire kidney is visualized on the image without excess abdominal signal deep to the individual kidney.
      • Less depth → greater magnification
    • Gain (amplification of returning signals):
      • Should be adjusted such that the renal parenchyma is visualized 
      • Too much signal leads to loss of detail.

Interpretation and evaluation

Report on:

  • Kidney size:
    • Normal: 10–12 cm 
    • Renal cortex should be > 6 mm MM Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Multiple Myeloma.
  • Echogenicity:
    • Renal cortex is homogeneous Homogeneous Imaging of the Spleen and usually slightly hypoechoic Hypoechoic A structure that produces a low-amplitude echo (darker grays) Ultrasound (Sonography) or isoechoic Isoechoic A structure that produces an echo of a very similar amplitude to its environment and is very difficult to distinguish Ultrasound (Sonography) relative to the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy.
    • Kidney with more echogenicity than the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy is abnormal.
  • Position: kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy are inferior to the left hemidiaphragm and liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy.
  • Associated structural abnormalities

Normal findings

Normal renal ultrasound:

  • Oval bean shape
  • Separated from the echogenic perirenal fat by a capsule Capsule An envelope of loose gel surrounding a bacterial cell which is associated with the virulence of pathogenic bacteria. Some capsules have a well-defined border, whereas others form a slime layer that trails off into the medium. Most capsules consist of relatively simple polysaccharides but there are some bacteria whose capsules are made of polypeptides. Bacteroides (a thin, linear structure)
  • Parenchyma:
  • Renal hilum Hilum Lungs: Anatomy: hyperechoic Hyperechoic A structure that produces a high-amplitude echo (lighter grays and white) Ultrasound (Sonography)
  • Ureter: 
    • Often not visualized owing to overlying tissue
    • Patency detected by Doppler Doppler Ultrasonography applying the doppler effect, with frequency-shifted ultrasound reflections produced by moving targets (usually red blood cells) in the bloodstream along the ultrasound axis in direct proportion to the velocity of movement of the targets, to determine both direction and velocity of blood flow. Ultrasound (Sonography) when urine Urine Liquid by-product of excretion produced in the kidneys, temporarily stored in the bladder until discharge through the urethra. Bowen Disease and Erythroplasia of Queyrat enters the bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess
  • Bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess: anechoic Anechoic A structure that produces no echo at all (looks completely black) Ultrasound (Sonography) rounded organ in the pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis: Anatomy
Normal adult kidney

Normal adult kidney:
Measurement of kidney length on the ultrasound is illustrated by plus signs and a dashed line.
*: column of Bertin
**: pyramid
***: cortex
****: sinus

Image: “Normal adult kidney. Measurement of kidney length on the US image is illustrated by ‘+’ and a dashed line. * Column of Bertin; ** pyramid; *** cortex; **** sinus.” by MDPI, Basel, Switzerland. License: CC BY 4.0

CT

Overview

  • Medical indications:
    • Follow-up for suspicious ultrasound image:
      • Hypoechoic Hypoechoic A structure that produces a low-amplitude echo (darker grays) Ultrasound (Sonography)/ hyperechoic Hyperechoic A structure that produces a high-amplitude echo (lighter grays and white) Ultrasound (Sonography) lesions
      • Concern for vascular pathology
      • Contour deformities
      • Urolithiasis
      • Hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis
    • Malignancy Malignancy Hemothorax:
    • Major trauma:
      • Evaluation of renal parenchyma
      • Evaluation for renal hemorrhage +/– active extravasation on delayed images
      • Concern for subtle pathology not seen on ultrasound
  • Advantages:
  • Disadvantages: 
    • High radiation Radiation Emission or propagation of acoustic waves (sound), electromagnetic energy waves (such as light; radio waves; gamma rays; or x-rays), or a stream of subatomic particles (such as electrons; neutrons; protons; or alpha particles). Osteosarcoma dose
    • Individual must hold still for exam.
    • Expensive

Exam technique

Standard CT scanning Standard CT scanning Imaging of the Liver and Biliary Tract:

  • Individual lies supine on table: 
    • Table is moved in a CT scanner, which rotates around the individual.
    • Individual is instructed to hold breath and remain still for scan (for seconds).
  • Exams can be done with or without IV or oral contrast:
    • Without contrast: used in evaluation of renal or ureteral calculi
    • Likewise, noncontrast studies serve as a baseline in evaluating lesion enhancement (when contrast is administered)
    • Timing of IV contrast dye can help direct radiology inquiry of certain areas of pathology.
    • Contrast study: 
      • Nephrogenic phase: evaluates the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy for any lesions
      • Excretory phase: evaluates the collecting system

Interpretation and evaluation

Interpretation should follow systematic and reproducible pattern.

  • History and examination are reviewed.
  • Ideal evaluation with soft-tissue window (W)/level (L): 400/50
  • Compare to available recent imaging of area of interest
  • Orient image:
  • Identify landmark anatomical structures.
  • Observe for “continuity” of parenchyma while scrolling through image slices.

Normal findings

  • Kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy:
  • Ureters Ureters One of a pair of thick-walled tubes that transports urine from the kidney pelvis to the urinary bladder. Urinary Tract: Anatomy:
  • Bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess
    • Rounded structure in the pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis: Anatomy
    • Both ureters Ureters One of a pair of thick-walled tubes that transports urine from the kidney pelvis to the urinary bladder. Urinary Tract: Anatomy and bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess are opacified with contrast studies.
Ct of the abdomen and pelvis (with contrast)

CT of the abdomen and pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis: Anatomy (with contrast):
From top left: sagittal Sagittal Computed Tomography (CT), coronal Coronal Computed Tomography (CT) plane, and axial Axial Computed Tomography (CT) plane, with 3-mm slice thickness. Images show normal anatomy.

Image: “CT of a normal abdomen and pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis: Anatomy, thumbnail” by Mikael Häggström. License: CC0 1.0

MRI

Overview

  • Medical indications:
    • Detailed evaluation of renal lesions
      • Hemangiomas
      • Cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change
      • Renal cell carcinoma Renal cell carcinoma Renal cell carcinoma (RCC) is a tumor that arises from the lining of the renal tubular system within the renal cortex. Renal cell carcinoma is responsible for 80%-85% of all primary renal neoplasms. Most RCCs arise sporadically, but smoking, hypertension, and obesity are linked to its development. Renal Cell Carcinoma
      • Indeterminate lesions noted incidentally on ultrasound and CT
    • Vascular disease ( MRA MRA Imaging of the Heart and Great Vessels for renal artery Renal artery A branch of the abdominal aorta which supplies the kidneys, adrenal glands and ureters. Glomerular Filtration aneurysms)
  • Advantages:
    • Provides higher level of imaging and detail of fluid, enhancement, and soft tissue Soft Tissue Soft Tissue Abscess
    • Can be used for evaluation of pregnant individuals
    • Used as adjunct to previous test (ultrasound/CT)
  • Disadvantages:
    • ↑↑↑ Cost
    • Takes much longer to perform than chest X-ray X-ray Penetrating electromagnetic radiation emitted when the inner orbital electrons of an atom are excited and release radiant energy. X-ray wavelengths range from 1 pm to 10 nm. Hard x-rays are the higher energy, shorter wavelength x-rays. Soft x-rays or grenz rays are less energetic and longer in wavelength. The short wavelength end of the x-ray spectrum overlaps the gamma rays wavelength range. The distinction between gamma rays and x-rays is based on their radiation source. Pulmonary Function Tests, CT, or ultrasonography
    • Not suitable for all individuals:
      • Implants (particularly metal) distort image.
      • Requires individual to be in a loud, enclosed space
      • Individual must stay still for adequate images.

Exam technique

Table: General principles of MRI
Tissue T1-weighted images T1-Weighted Images Imaging of the Head and Brain T2-weighted images T2-Weighted Images Imaging of the Head and Brain
Fluid (e.g.,CSF) Dark Bright
Fat Bright Bright
Inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body’s defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation Dark Bright

Interpretation and evaluation

Interpretation should follow a systematic and reproducible pattern:

  • Review the individual’s history and physical examination information.
  • Compare to available recent imaging of the area of interest.
  • Orient image.
  • Identify landmark anatomical structures.
  • Observe for “continuity” of structures while scrolling through image slices.

Normal findings

  • Normal renal/kidney MRI appearance: 
    • Crescent-shaped structure
    • Smooth borders
    • Homogeneous Homogeneous Imaging of the Spleen cortex signal
    • Intensity: 
      • T1-weighted: slightly less intense than the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy
      • T2-weighted: more intense than the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver: Anatomy
    • Contrast:
  • Both ureters Ureters One of a pair of thick-walled tubes that transports urine from the kidney pelvis to the urinary bladder. Urinary Tract: Anatomy and bladder Bladder A musculomembranous sac along the urinary tract. Urine flows from the kidneys into the bladder via the ureters, and is held there until urination. Pyelonephritis and Perinephric Abscess are also well visualized.

Abnormal Findings

Nephrolithiasis Nephrolithiasis Nephrolithiasis is the formation of a stone, or calculus, anywhere along the urinary tract caused by precipitations of solutes in the urine. The most common type of kidney stone is the calcium oxalate stone, but other types include calcium phosphate, struvite (ammonium magnesium phosphate), uric acid, and cystine stones. Nephrolithiasis

  • Radiography: radiopaque Radiopaque An object of high density that blocks X-rays (looks white) X-rays calculi are visualized (but some stones may be radiolucent Radiolucent An object of low density that is permeable to X-rays (looks black) X-rays).
  • Ultrasonography:
    • Nephrolithiasis Nephrolithiasis Nephrolithiasis is the formation of a stone, or calculus, anywhere along the urinary tract caused by precipitations of solutes in the urine. The most common type of kidney stone is the calcium oxalate stone, but other types include calcium phosphate, struvite (ammonium magnesium phosphate), uric acid, and cystine stones. Nephrolithiasis:
      • +/– hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis
      • Hyperechoic Hyperechoic A structure that produces a high-amplitude echo (lighter grays and white) Ultrasound (Sonography) foci (stone) 
      • +/– posterior shadowing
    • Hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis:
      • Anechoic Anechoic A structure that produces no echo at all (looks completely black) Ultrasound (Sonography) fluid-filled interconnected space
      • Spectrum of dilation of the renal calyces
  • CT:
    • Method of choice for renal stones owing to:
      • High sensitivity and specificity Sensitivity and Specificity Binary classification measures to assess test results. Sensitivity or recall rate is the proportion of true positives. Specificity is the probability of correctly determining the absence of a condition. Epidemiological Values of Diagnostic Tests
      • No contrast needed (best method: non-enhanced CT)
      • No patient preparation
      • Not operator-dependent
    • Features:
      • Hyperdense lesion (stone)
      • Hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis (enlargement of the renal collecting system) noted if there is an obstruction
      • +/– hydroureter

Pyelonephritis Pyelonephritis Pyelonephritis is infection affecting the renal pelvis and the renal parenchyma. This condition arises mostly as a complication of bladder infection that ascends to the upper urinary tract. Pyelonephritis can be acute or chronic (which results from persistent or chronic infections). Typical acute symptoms are flank pain, fever, and nausea with vomiting. T Pyelonephritis and Perinephric Abscess

  • Infection affecting the renal pelvis Renal pelvis Kidneys: Anatomy and the renal parenchyma
  • Can be diagnosed clinically, but no response in 48–72 hours prompts obtaining imaging studies
  • Ultrasonography:
    • Debris in the collecting system (internal echoes)
    • Reduced areas of cortical vascularity 
    • Loss of normal demarcation
    • Focal hypoechoic Hypoechoic A structure that produces a low-amplitude echo (darker grays) Ultrasound (Sonography) areas ( edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema)
    • Hyperechoic Hyperechoic A structure that produces a high-amplitude echo (lighter grays and white) Ultrasound (Sonography) areas (hemorrhage)
    • +/– perinephric abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease ( hypoechoic Hypoechoic A structure that produces a low-amplitude echo (darker grays) Ultrasound (Sonography) or mixed echogenicity fluid collection)
  • CT:
    • Method of choice (unenhanced images followed by contrast-enhanced study)
    • Features may include:
      • Swollen, edematous kidney (appearing less dense)
      • Fat stranding
      • Focal wedge-like regions with reduced enhancement compared with the normal portions of the kidney  
      • Perinephric abscess Abscess Accumulation of purulent material in tissues, organs, or circumscribed spaces, usually associated with signs of infection. Chronic Granulomatous Disease (soft-tissue or fluid attenuation within the perirenal space)

Renal infarction

  • Loss of renal tissue resulting from the disruption of renal blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure
  • Major causes are thromboemboli and in situ thrombosis Thrombosis Formation and development of a thrombus or blood clot in the blood vessel. Epidemic Typhus.
  • Ultrasonography:
    • Complete or segmental blood flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure absence (color Doppler Doppler Ultrasonography applying the doppler effect, with frequency-shifted ultrasound reflections produced by moving targets (usually red blood cells) in the bloodstream along the ultrasound axis in direct proportion to the velocity of movement of the targets, to determine both direction and velocity of blood flow. Ultrasound (Sonography))
    • Contrast-enhanced ultrasonography can detect infarcts.
    • Infarcted area:
      • Hypoechoic Hypoechoic A structure that produces a low-amplitude echo (darker grays) Ultrasound (Sonography)  
      • Wedge-shaped region or patchy areas of reduced perfusion
      • Well defined 
  • CT:
    • Non-contrast CT is the initial test for the presentation Presentation The position or orientation of the fetus at near term or during obstetric labor, determined by its relation to the spine of the mother and the birth canal. The normal position is a vertical, cephalic presentation with the fetal vertex flexed on the neck. Normal and Abnormal Labor of flank pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways (since kidney stones Kidney stones Nephrolithiasis is the formation of a stone, or calculus, anywhere along the urinary tract caused by precipitations of solutes in the urine. The most common type of kidney stone is the calcium oxalate stone, but other types include calcium phosphate, struvite (ammonium magnesium phosphate), uric acid, and cystine stones. Nephrolithiasis are more common).
    • But renal infarcts are most often identified with contrast-enhanced CT:
      • Classic finding: wedge-shaped lesion/perfusion defect
      • Hypodense
      • Well defined 
      • Arterial phase may show the thrombus/embolus or dissection.
  • MRI with gadolinium Gadolinium An element of the rare earth family of metals. It has the atomic symbol gd, atomic number 64, and atomic weight 157. 25. Its oxide is used in the control rods of some nuclear reactors. Magnetic Resonance Imaging (MRI) is an alternative to CT.

Renal cysts Cysts Any fluid-filled closed cavity or sac that is lined by an epithelium. Cysts can be of normal, abnormal, non-neoplastic, or neoplastic tissues. Fibrocystic Change

Renal cell carcinoma Renal cell carcinoma Renal cell carcinoma (RCC) is a tumor that arises from the lining of the renal tubular system within the renal cortex. Renal cell carcinoma is responsible for 80%-85% of all primary renal neoplasms. Most RCCs arise sporadically, but smoking, hypertension, and obesity are linked to its development. Renal Cell Carcinoma

  • Most common primary renal neoplasm
  • Malignancy Malignancy Hemothorax originates from the cortex.
  • Ultrasonography (less sensitive than CT):
  • CT:
    • Method of choice (multiphasic CT scan of the abdomen and pelvis Pelvis The pelvis consists of the bony pelvic girdle, the muscular and ligamentous pelvic floor, and the pelvic cavity, which contains viscera, vessels, and multiple nerves and muscles. The pelvic girdle, composed of 2 “hip” bones and the sacrum, is a ring-like bony structure of the axial skeleton that links the vertebral column with the lower extremities. Pelvis: Anatomy)
    • Features:
      • May be solid masses or complex cystic Cystic Fibrocystic Change masses
      • Indeterminate density 
      • Ill-defined border
      • Irregular enhancement
      • +/– calcification
      • +/– necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage (hypodense)
      • +/– renal veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology and inferior vena cava Inferior vena cava The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels: Anatomy extension Extension Examination of the Upper Limbs
  • MRI:
    • Alternative in cases of iodinated contrast allergy Allergy An abnormal adaptive immune response that may or may not involve antigen-specific IgE Type I Hypersensitivity Reaction or if with inconclusive ultrasound/CT 
    • Features may be: 
      • Solid masses 
      • Complex cystic Cystic Fibrocystic Change masses
      • Indeterminate density 
      • Ill-defined border
      • Irregular enhancement
      • +/– calcification
      • +/– necrosis Necrosis The death of cells in an organ or tissue due to disease, injury or failure of the blood supply. Ischemic Cell Damage
      • +/– renal veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins: Histology and inferior vena cava Inferior vena cava The venous trunk which receives blood from the lower extremities and from the pelvic and abdominal organs. Mediastinum and Great Vessels: Anatomy extension Extension Examination of the Upper Limbs

Other renal abnormalities

  • Angiomyolipoma Angiomyolipoma A benign tumor containing vascular, adipose, and muscle elements. It occurs most often in the kidney with smooth muscle elements (angiolipoleiomyoma) in association with tuberous sclerosis. Tuberous Sclerosis:
    • Most common benign Benign Fibroadenoma kidney tumor Tumor Inflammation
    • Made of varying amounts of fat, blood vessels, and smooth muscle 
    • Imaging: CT with and without contrast
      • Cortical lesion is well defined.
      • + Intralesional fat density
  • Renal agenesis Renal Agenesis Congenital Renal Abnormalities
    • Developmental renal defect, which can be unilateral or bilateral
    • Prenatal diagnosis relies on ultrasonography, which shows:
      • Empty renal fossa
      • Large contralateral kidney
      • Congenital Congenital Chorioretinitis elongation Elongation Polymerase Chain Reaction (PCR) of the ipsilateral adrenal gland
      • Color flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure Doppler Doppler Ultrasonography applying the doppler effect, with frequency-shifted ultrasound reflections produced by moving targets (usually red blood cells) in the bloodstream along the ultrasound axis in direct proportion to the velocity of movement of the targets, to determine both direction and velocity of blood flow. Ultrasound (Sonography) will fail to show renal vessel(s).
  • Horseshoe kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy:
    • Involves abnormal migration of both kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy
    • Fusion of both kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys: Anatomy at their inferior poles
    • Often located below the inferior mesenteric artery Inferior mesenteric artery The artery supplying nearly all the left half of the transverse colon, the whole of the descending colon, the sigmoid colon, and the greater part of the rectum. It is smaller than the superior mesenteric artery and arises from the aorta above its bifurcation into the common iliac arteries. Small Intestine: Anatomy
    • Presentation Presentation The position or orientation of the fetus at near term or during obstetric labor, determined by its relation to the spine of the mother and the birth canal. The normal position is a vertical, cephalic presentation with the fetal vertex flexed on the neck. Normal and Abnormal Labor is often without symptoms, with the anomaly detected with antenatal ultrasonography.
    • In others, imaging workup is directed toward the presenting symptoms, including: 
      • Pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways
      • Hematuria Hematuria Presence of blood in the urine. Renal Cell Carcinoma
      • Urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract: Anatomy infection 
      • Obstruction
  • Crossed kidney ectopia: 
    • Kidney and ureter cross the midline, reaching the other side (to the contralateral kidney), with or without fusion.
    • The contralateral kidney may be in its normal position or positioned lower.
    • More often an incidental finding on either ultrasonography or CT.
      • No kidney in the renal fossa
      • Kidney found in the other side, with the other kidney

References

  1. Faubel, S., Patel, N. U., Lockhart, M. E., Cadnapaphornchai, M. A. (2014). Renal relevant radiology: use of ultrasonography in patients with AKI. Clin J Am Soc Nephrol 9:382–394. https://doi.org/10.2215/CJN.04840513
  2. Gash J.R., Noe J (2011). Radiology of the urinary tract. Chapter 9 of Chen M.M., Pope T.L., Ott D.J. (Eds.), Basic Radiology, 2nd ed. McGraw Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=360&sectionid=39669018
  3. Hansen, K.L., Nielsen, M.B., Ewertsen, C. (2015). Ultrasonography of the kidney: a pictorial review. Diagnostics 6(1):2. https://doi.org/10.3390/diagnostics6010002
  4. Hiorns, M.P. (2011). Imaging of the urinary tract: the role of CT and MRI. Pediatr Nephrol 26:59–68. https://doi.org/10.1007/s00467-010-1645-4
  5. Kruskal, J., Richie, J. (2021) Simple and complex kidney cysts in adults. UpToDate. Retrieved December 15, 2021, from https://www.uptodate.com/contents/renal-ectopic-and-fusion-anomalies
  6. Rosenblum, N. (2021) Renal ectopic and fusion anomalies. UpToDate. Retrieved Dec 14, 2021 from https://www.uptodate.com/contents/renal-ectopic-and-fusion-anomalies
  7. Salem, U., Matta, E.J., Youssef, A., Elsayes, K.M. (2014). Genitourinary system. In: Elsayes, K.M., Oldham, S.A. (Eds.),  Introduction to Diagnostic Radiology. McGraw-Hill. https://accessmedicine.mhmedical.com/content.aspx?bookid=1562&sectionid=95877752

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