Layers of the Meninges
The meninges are layers of connective tissue that protect the brain and spinal cord.
The meninges consist of 3 layers of connective tissue, with potential spaces between them:
- Dura mater: outermost layer
- Arachnoid mater: middle layer
- Pia mater: innermost layer
|Arachnoid mater (leptomeninges)||Neural crest|
|Subarachnoid space||Choroid plexus|
|Pia mater (leptomeninges)||Neural crest|
Dural Foldings, Reflections, and Sinuses
The dura mater is the thickest layer of the meninges and provides structure to the brain.
Dural foldings and dural sinuses come from the dura mater.
- Dural foldings separate the right and left hemispheres:
- Falx cerebri
- Falx cerebelli
- Tentorium cerebelli
- Diaphragma sellae
- Dural sinuses (venous sinuses) form between layers of dura mater. CSF flows through the dural sinuses.
|Falx cerebri||Separates the right and left cerebral hemispheres|
|Falx cerebelli||Separates the right and left cerebellar hemispheres|
|Tentorium cerebelli||Tent, or roof, over the cerebellum|
|Diaphragma sellae||The roof over the pituitary gland|
|Dural sinuses||The 2 layers of dura mater run together throughout most of the skull. Where they separate, the gap between them is called a dural venous sinus. These sinuses drain blood and CSF from the brain and empty into the internal jugular vein.|
- Meningiomas are the most common cranial neoplasm, arising arise from arachnoidal cells that are found in the arachnoid villi. Meningiomas are typically benign, slow-growing tumors, but they can sometimes present in an atypical or malignant fashion. Symptoms of meningiomas depend on their location. The symptoms occur as a result of the tumor compressing nearby structures. The most common treatment is surgical excision.
- Meningitis: inflammation of the meninges that surround the brain and spinal cord. In general, meningitis causes symptoms such as headache, fever, and stiff neck. This disease is subdivided into bacterial (most common cause), viral, and parasitic meningitis. Infectious etiologies are diagnosed with a lumbar puncture and must be treated aggressively with antimicrobial medications.
- Epidural hemorrhage: bleeding in the space external to the dura mater—right beneath the skull. Epidural hemorrhage most commonly occurs after direct trauma to the head. Patients present with loss of consciousness after a direct blow to the head and, occasionally, altered mental status. If symptomatic, patients should undergo craniotomy with evacuation of the hematoma.
- Subdural hemorrhage: occurs beneath the dura mater and is usually more chronic than epidural hemorrhages. In infants, subdural hemorrhage typically occurs as a result of child abuse. In young adults, common causes include bike or car accidents; and in elderly adults, subdural bleeds are usually the result of falls. If symptomatic, patients should undergo craniotomy with evacuation of the hematoma.
- Dural sinus thrombosis: blood clots can form in the dural sinuses as a result of trauma or infection. Dural sinus thrombosis can lead to hemorrhagic infarction and cerebral edema. A cavernous sinus thrombosis is a subtype of dural sinus thrombosis that occurs because of seeding of an infection from the nasal area.
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