Cardiac Myxoma

Cardiac myxoma is the most common of the primary tumors of the adult heart, all of which are very rare. Cardiac myxoma is a benign neoplasm that arises from primitive multipotent mesenchymal cells. Most occur sporadically, but some are a part of some familial syndromes. All 4 chambers may give rise to myxoma, but 90% originate and grow in the atria, with a left-to-right ratio of approximately 4:1. Diagnosis is made by echocardiography, cardiac magnetic resonance imaging (MRI), or cardiac computed tomography (CT). Complete surgical excision is required because of the substantial risk of embolization and cardiovascular complications, including sudden death.

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Overview

Definition

Cardiac myxoma is a benign primary tumor of the heart.

Epidemiology

  • Primary cardiac tumors are very rare: incidence < 0.1%
  • Myxoma is the most common primary cardiac tumor.
  • Most common in adults, but can happen in all age groups
  • 90% of cardiac myxomas arise in the atria, with left-to-right ratio of 4:1.
  • Women > men
  • Most are sporadic.
  • Most common inherited form is a part of Carney complex:
    • Autosomal dominant disorder:
      • Atrial and extracardiac myxomas
      • Schwannomas
      • Pigmentation abnormalities
      • Endocrine and other tumors 
    • Not the same as Carney triad or Carney-Stratakis syndrome

Etiology

  • Arises from primitive multipotent mesenchymal cells 
  • No consistent genetic alterations in sporadic myxomas
  • Growth factors may contribute to tumor formation, e.g., vascular endothelial growth factor (VEGF), an angiogenic factor.
  • Familial syndromes with myxomas are associated with specific genetic defects:
    • Carney complex: null mutations in PRKAR1A, encoding a regulatory subunit of a cyclic-AMP–dependent protein kinase
    • Mazabraud’s syndrome: single or multiple intramuscular myxomas with fibrous dysplasia; activate mutations in the GNAS1 gene

Pathophysiology

Anatomy and histology

  • 80% originate in the left atrium (most commonly, fossa ovalis).
  • Most others are in the right atrium.
  • Range from 1–15 cm in diameter
  • Typically pedunculated tumors with gelationous consistency
  • Microscopic features:
    • Scattered stellate or globular cells in the mucopolysaccharide stroma
    • Can be accompanied by hemorrhage and chronic inflammation
    • Small tumors tend to be villous and friable.
    • Larger tumors usually have a smooth surface.

Surgical gross pathology specimens (A, B, C, D, E) and histologic (F) findings of bilateral atrial myxomas
A: myxoma from left atrium
B: myxoma from right atrium
C: embolic myxoma from aortic bifurcation
D: embolic myxoma from left popliteal artery
E: embolic myxoma from right popliteal artery
F: histologic findings of myxoma (H&E (hematoxylin and eosin) x400): characteristic stellate tumor cells within an abundant myxoid stroma

Image: “Myxoma” by Division of Cardiology, Department of Internal Medicine, College of Medicine, Hanyang University, Seungdong-Gu, Heangdang-Dong 17, 133-070 Seoul, South Korea. License: CC BY 4.0

Pathophysiologic mechanisms

  • Obstruction of blood flow: causes heart failure
  • Interference with cardiac valves: 
    • More common with pedunculated myxomas
    • Regurgitation
  • Embolization:
    • More common with small tumors (from fragments or surface thrombi)
    • More commonly systemic than pulmonic
  • Direct invasion of the myocardium:
    • Left ventricular dysfunction
    • Arrhythmias/heart block
    • Pericardial effusion
  • Invasion of the adjacent lung (can mimic lung cancer)
  • Cytokine production (e.g., interleukin-6)

Clinical Presentation

Left-side myxomas (approximately 85%)

  • Symptoms similar to mitral valve stenosis or regurgitation (left heart failure):
    • Dyspnea
    • Orthopnea
    • Paroxysmal nocturnal dyspnea
    • Cough/hemoptysis
    • Edema
    • Fatigue
  • Neurologic symptoms: secondary to systemic emboli
  • Arrhythmias

Right-side myxomas (approximately 15%)

  • Symptoms of tricuspid disease (right heart failure):
    • Fatigue
    • Peripheral edema
    • Hepatomegaly
    • Ascites
    • Syncope
    • Sudden death
  • Pulmonary embolism
  • If patent foramen ovale is present:
    • Systemic emboli
    • Hypoxemia (from shunting of venous blood from the right side)

Constitutional symptoms

  • May be seen in 30% of patients 
  • Cytokine release:
    • Fever
    • Weight loss
    • Fatigue

Diagnosis and Management

Physical examination

  • Left atrial tumors:
    • Diastolic “tumor plop” on auscultation
    • Pulmonary edema: rales or crackles on auscultation
  • Right atrial tumors:
    • Diastolic murmur
    • Jugular venous distention
    • Generalized edema
    • Hepatomegaly
    • Abdominal ascites

Imaging

  • Echocardiography (usually 1st imaging technique):
    • Transesophageal echocardiography (TEE) gives better resolution.
    • Can usually identify:
      • Mass
      • Mobility
      • Obstruction
      • Embolization 
  • Cardiac magnetic resonance imaging (CMR): detailed anatomic imaging
  • Cardiac computed tomography (CCT): if CMR not available
  • Positron emission tomography (PET) scan helps differentiate:
    • Metastatic tumors versus atrial myxoma 
    • Lipomatous septal hypertrophy versus atrial myxoma
  • Coronary angiography: 
    • “Sea anemone” appearance on angiography
    • Mapping of blood supply: may be needed for surgical planning

Transvenous biopsy

  • Risk of embolism
  • Should only be performed if diagnosis is uncertain and benefits outweigh the risks

Management

  • Surgical resection is required because of:
    • Risk of embolization
    • Cardiovascular complications
    • Risk of sudden death
  • Prognosis: 
    • Operative mortality rate < 5%
    • Recurrence: 2%–5% of cases, more common if familial or multiple
    • Cardiac autotransplantation (with atrial reconstruction) or transplantation may be necessary for recurrent atrial myxoma.
    • Atrial arrhythmias or atrioventricular conduction abnormalities in 26%

Gross pathology of excised left atrial myxoma, measuring 7 × 6 × 4 cm: Note the translucency of the tumor, due to its abundant content of acid mucopolysaccharide ground substance.

Image: “Gross pathology” by Department of Neurology, Hospital of International University of Health and Welfare, 537-3 Iguchi, Nasushiobara, Tochigi 329-2763, Japan. License: CC BY 3.0

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Differential Diagnosis

Benign primary cardiac tumors or tumor-like masses

  • Intracardiac thrombus: the most common type of intracardiac mass in adults. May occur following myocardial infarction with ventricular thrombus formation, or with atrial fibrillation and mitral stenosis where atrial thrombi predominate. Left-sided thrombi are a common source of stroke and other arterial embolic syndromes. Ultrasound and CMR aid in the diagnosis. Treatment is usually with anticoagulation.
  • Rhabdomyoma: the most common pediatric cardiac tumor; a benign neoplasm of muscle cells, often multiple, associated with tuberous sclerosis. Frequently undergoes spontaneous regression; diagnosis is made by clinical impression and imaging.
  • Fibromas: 2nd most common primary pediatric cardiac tumor. Composed of fibroblasts, which usually arise in ventricular septum. Fibromas may be part of Gorlin syndrome (nevoid basal cell carcinoma syndrome); does not regress, but may not need treatment if small.
  • Lipomas: rare encapsulated neoplasm of mature fat cells. May originate from subendocardium, subpericardium, or from the myocardium. Lipomas are more frequent in the left ventricle or right atrium.
  • Papillary fibroelastoma: the 2nd most common primary cardiac tumor in adults. Papillary fibroelastoma are small sea anemone–shaped endocardial tumors with frond-like structures, usually on mitral or aortic valves, where they can cause symptoms due to embolization, either of the tumor itself or thrombus. Imaging is diagnostic, and surgery is recommended.

Malignant tumors of the heart

  • Sarcoma: malignant tumor originating from the connective tissue cells. Exceedingly rare in the heart. Angiosarcoma is the most common type. Prognosis is poor, as these tumors tend to grow rapidly and recur even when completely resected.
  • Metastatic tumors: 20 times more common than primary tumors. May be present in 20% of patients dying of cancer. Symptoms depend on the site of cardiac involvement. Diagnosis is made with echocardiography, CMR, or CCT.

References

  1. Valvular Heart Disease. (2020). In Kumar, V., Abbas, A. K., Aster, J.C., (Eds.). Robbins & Cotran Pathologic Basis of Disease. (10th ed., p. 579).
  2. Gaasch, W.H., Salm, T.J.V. (2020). Cardiac tumors. UpToDate. Retrieved December 17, 2020, from https://www.uptodate.com/contents/cardiac-tumors?search=Atrial%20myxoma&source=search_result&selectedTitle=1~46&usage_type=default&display_rank=1#H12461347
  3. Kuon, E., Kreplin, M., Weiss, W., Dahm, J.B. (2004). The challenge presented by right atrial myxoma. Herz. 2004 Nov;29(7):702-9. doi: 10.1007/s00059-004-2571-7. PMID: 15580325.

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