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Summary Table

Category	Details
Risk Factors	Middle-aged to older women (peak 60s-70s, F:M ratio ~2:1), prior cranial radiation, Neurofibromatosis Type 2 (NF2), obesity, hormone replacement therapy
Etiology	Neoplastic proliferation of arachnoid cap cells (meningothelial cells) of the arachnoid mater; loss of chromosome 22q / NF2 gene mutations in sporadic and NF2-associated cases
Patient Presentation	Slowly progressive headaches, focal neurological deficits based on tumor location, new-onset seizures in an older adult; symptoms evolve over months to years
Classic Physical Exam	Focal deficits corresponding to location: leg weakness (parasagittal/falx), anosmia with ipsilateral optic atrophy and contralateral papilledema (olfactory groove / Foster Kennedy syndrome), proptosis (sphenoid wing), hearing loss and facial numbness (cerebellopontine angle)
Key Diagnostic Results	MRI with contrast: homogeneously enhancing, well-circumscribed extra-axial mass with dural tail sign. CT: hyperdense lesion with calcification and possible hyperostosis of overlying bone. Histology: psammoma bodies, whorled cell pattern, EMA-positive
Management	Observation with serial imaging (small, asymptomatic). Surgical resection for symptomatic or growing tumors (definitive). Radiation therapy or stereotactic radiosurgery for unresectable, residual, or recurrent disease
Keywords	"Extra-axial mass," "dural tail sign," "psammoma bodies," "whorled pattern," "calcified intracranial mass in older woman," "hyperostosis," "Foster Kennedy syndrome," "NF2 with multiple meningiomas"

1. Pathophysiology

Meningiomas arise from arachnoid cap (meningothelial) cells, which are components of the arachnoid granulations. Because these cells sit outside the brain parenchyma, meningiomas are classified as extra-axial tumors. This distinction is critical on the exam: meningiomas compress the brain from outside rather than infiltrating it, which is why they are typically well-circumscribed on imaging and often surgically curable when accessible.

The molecular driver in both sporadic and NF2-associated meningiomas is loss of the NF2 tumor suppressor gene on chromosome 22q12. The NF2 gene encodes merlin, a cytoskeletal protein that normally functions as a growth regulator. Loss of merlin removes a brake on cell proliferation, allowing unchecked growth of arachnoid cap cells. In NF2 patients, bilateral germline mutations lead to multiple meningiomas, often presenting at a younger age than sporadic cases.

The strong female predominance (roughly 2:1) is explained by the expression of progesterone receptors on meningioma cells. This has direct clinical consequences: meningiomas may enlarge during pregnancy or with exogenous progesterone exposure. Test writers may present a pregnant patient with worsening neurological symptoms and an extra-axial mass to test this association.

Because meningiomas are slow-growing tumors, the brain has time to accommodate the mass. Patients often present late, with gradually worsening symptoms over months to years. The clinical presentation is determined entirely by anatomical location, because the tumor compresses whatever structure lies beneath it. A parasagittal meningioma compresses the motor cortex for the lower extremities (the medial cortical surface corresponds to the leg homunculus), causing progressive leg weakness. An olfactory groove meningioma compresses the olfactory nerve and eventually the optic nerve, producing the classic Foster Kennedy syndrome: ipsilateral anosmia, ipsilateral optic atrophy (from direct compression), and contralateral papilledema (from raised intracranial pressure).

Meningiomas can induce reactive hyperostosis of the overlying skull bone through osteoblast stimulation and direct bony invasion. This is a distinguishing feature that can be visible on CT and is virtually pathognomonic when present with an enhancing extra-axial mass.

On histology, the hallmark finding is psammoma bodies, which are laminated concentric calcifications. These also appear in other tumors of similar embryological origin (papillary thyroid carcinoma, serous papillary ovarian carcinoma), so the exam may test the association of psammoma bodies across these entities. The whorled arrangement of spindle-shaped meningothelial cells is another classic microscopic descriptor.

2. Classification and Clinical Manifestation

WHO Grading

Grade	Designation	Frequency	Histological Subtypes	Behavior
Grade I	Benign	~80%	Meningothelial, fibrous (fibroblastic), transitional (mixed), psammomatous, angiomatous, secretory	Slow-growing, low recurrence after complete resection
Grade II	Atypical	~15-18%	Atypical, clear cell, chordoid	Increased mitotic activity ($\geq 4$ mitoses per 10 HPF), brain invasion possible, higher recurrence rate
Grade III	Anaplastic (malignant)	~2-3%	Anaplastic, papillary, rhabdoid	Aggressive, high recurrence, poor prognosis, may metastasize

By Location

Location	Frequency	Classic Presentation
Parasagittal / Falx	~25%	Progressive bilateral or unilateral leg weakness (compression of medial motor strip), seizures
Convexity	~20%	Focal motor or sensory deficits corresponding to cortical area, seizures, headache
Sphenoid wing	~15-20%	Medial: visual loss, cranial nerve palsies (III, IV, VI). Lateral: temporal lobe seizures, proptosis, fullness of the temporal fossa
Olfactory groove	~10%	Anosmia (often bilateral), personality changes (frontal lobe), Foster Kennedy syndrome
Cerebellopontine angle (CPA)	~5-10%	Sensorineural hearing loss, facial numbness (CN V), facial weakness (CN VII); mimics vestibular schwannoma
Tuberculum sellae / Suprasellar	~5-10%	Bitemporal hemianopia (optic chiasm compression), visual acuity loss
Posterior fossa / Foramen magnum	~5%	Progressive spastic quadriparesis (upper extremity predominant), lower cranial nerve palsies, neck pain
Intraventricular	~1-2%	Obstructive hydrocephalus, headaches, gait disturbance
Spinal	~10% of all meningiomas	Progressive myelopathy with cord compression, thoracic spine predominance, strong female predominance

3. Diagnostic Workup

Test	Role	Key Findings
MRI brain with gadolinium contrast	Best initial test and primary diagnostic modality	Homogeneously enhancing, well-circumscribed extra-axial mass; dural tail sign (enhancing thickened dura extending from tumor margin); broad dural base; T1 isointense, T2 iso- to hyperintense; clear CSF cleft between tumor and brain
CT head without contrast	Often the first study obtained (e.g., in ER for new seizure or headache)	Hyperdense, well-circumscribed extra-axial mass; calcification within tumor; hyperostosis of adjacent bone
CT with contrast	Alternative when MRI is unavailable	Intense homogeneous enhancement
Cerebral angiography	Preoperative planning (not routine)	Sunburst / spoke-wheel pattern of vascularity; tumor blush from meningeal artery feeders (middle meningeal artery most common); used to guide preoperative embolization
Histopathology	Confirmatory / Gold standard	Whorled meningothelial cell clusters, psammoma bodies, positive for EMA (epithelial membrane antigen), vimentin-positive, WHO grading determines prognosis

In clinical practice (and on exams), the workup often begins with a non-contrast CT obtained for an older patient presenting with new headache or seizure. The CT reveals a hyperdense, calcified, well-demarcated extra-axial mass, sometimes with hyperostosis. This appearance is highly suggestive of meningioma, and the next step is to obtain an MRI with gadolinium contrast, which is the best diagnostic study.

On MRI, the cardinal feature is a dural tail sign: a linear enhancement of the thickened dura radiating from the margin of the tumor. While the dural tail is not 100% pathognomonic (it can occur rarely with dural metastases or lymphoma), in the context of a well-circumscribed, broadly dural-based, homogeneously enhancing extra-axial mass, it is essentially diagnostic. The exam may test your ability to distinguish extra-axial from intra-axial tumors. Key clues for extra-axial include: the CSF cleft between tumor and brain, buckling of the gray-white junction inward, and a broad dural base.

The distinction between MRI characteristics and histological confirmation is important. The imaging is often so characteristic that biopsy is not required before proceeding to surgery in classic presentations. Histopathology provides definitive diagnosis and WHO grading after surgical resection. The classic histological findings are psammoma bodies (laminated concentric calcifications) and a whorled pattern of meningothelial cells. Immunohistochemistry shows positivity for EMA and vimentin, which distinguishes meningioma from other dural-based lesions like solitary fibrous tumor (which is CD34-positive, EMA-negative).

If preoperative embolization is considered (to reduce intraoperative bleeding), catheter angiography reveals a characteristic sunburst or spoke-wheel pattern of vascularity, with feeding vessels from meningeal arteries.

4. Management and Treatment

Clinical Scenario	Management	Details
Small, asymptomatic, incidental	Observation with serial MRI	Repeat MRI at 3-6 months, then annually if stable; common in elderly patients with incidental findings
Symptomatic or growing	Surgical resection (primary treatment)	Goal: gross total resection including involved dura and bone (Simpson Grade I); extent of resection predicts recurrence
Perioperative seizure control	Antiepileptic drugs (AEDs)	Levetiracetam is commonly used perioperatively if the patient has seizures; prophylactic AEDs in seizure-naive patients are not routinely recommended long-term
Perioperative edema	Dexamethasone	Reduces peritumoral vasogenic edema; taper postoperatively
Unresectable or subtotally resected WHO Grade I	Stereotactic radiosurgery (SRS)	Gamma Knife or CyberKnife for tumors $\leq 3$ cm; excellent local control rates
WHO Grade II (atypical)	Surgery + adjuvant radiation therapy	External beam radiation therapy (EBRT) after subtotal resection or at recurrence; observation may follow gross total resection in some protocols
WHO Grade III (anaplastic)	Surgery + adjuvant radiation therapy	EBRT is routinely recommended regardless of resection extent due to high recurrence rate
Recurrent meningioma	Reoperation, radiation, or both	Consider SRS for small recurrences; systemic therapy (e.g., somatostatin analogues, bevacizumab) has limited evidence and is used for refractory cases
Preoperative embolization	Endovascular embolization of feeding arteries	Performed 24-72 hours before surgery to reduce intraoperative blood loss for highly vascular tumors

Observation is appropriate for small, incidental meningiomas discovered on imaging obtained for unrelated reasons, particularly in elderly patients or those with comorbidities. Growth rates average 2-4 mm per year, and many meningiomas remain stable for years. Serial MRI is performed at 3 to 6 months after diagnosis to establish a growth trajectory, then annually if stable.

When intervention is indicated (symptoms, documented growth, or significant mass effect), surgical resection is the definitive treatment. The extent of resection is the strongest predictor of recurrence and is classified using the Simpson Grading System:

Simpson Grade	Extent of Resection	10-Year Recurrence Rate
I	Complete removal of tumor, dura, and abnormal bone	~10%
II	Complete tumor removal with coagulation (not excision) of dural attachment	~20%
III	Complete tumor removal without dural resection or coagulation	~30%
IV	Subtotal resection (partial tumor left behind)	~40%
V	Decompression or biopsy only	Progression expected

Exam questions may test the concept that leaving involved dura behind increases recurrence risk. Simpson Grade I resection is the goal whenever anatomically feasible.

Dexamethasone is given perioperatively to reduce vasogenic edema surrounding the tumor. The dose typically starts at 4 mg IV every 6 hours, tapered over days to weeks postoperatively based on clinical response.

Radiation therapy is reserved for cases where complete surgical resection is not achievable. Stereotactic radiosurgery (SRS) delivers a focused, high-dose single fraction to small tumors ($\leq 3$ cm) and is an alternative for patients who are poor surgical candidates. For atypical (Grade II) and anaplastic (Grade III) meningiomas, adjuvant external beam radiation therapy after surgery reduces recurrence. There is no established role for conventional chemotherapy in meningioma management, which is an important distinction from primary malignant brain tumors like glioblastoma.

The exam may present a pregnant patient with a growing meningioma to test the understanding that these tumors express progesterone receptors and may enlarge during pregnancy. Management in pregnancy is conservative when possible (dexamethasone for edema, delivery planning, and postpartum surgical evaluation), with surgery reserved for acute neurological deterioration.

5. Differential Diagnosis and Distractors

Differential	Why It Is Similar	Key Discriminator
Vestibular schwannoma (acoustic neuroma)	Both occur at the cerebellopontine angle; both present with hearing loss and cranial nerve deficits	Schwannoma is centered on the internal auditory canal (IAC) and causes IAC widening; meningioma has a broad dural base and does not widen the IAC. Schwannoma is S100-positive, not EMA-positive. Bilateral schwannomas = NF2, but NF2 also causes multiple meningiomas
Dural metastasis	Both are dural-based, enhancing masses; both can show a dural tail	Metastasis has a known primary malignancy (breast, lung, prostate); often irregular margins, surrounding edema disproportionate to size, may be multiple; clinical course is weeks to months, not years
Solitary fibrous tumor / Hemangiopericytoma	Both are dural-based enhancing extra-axial masses; both can appear well-circumscribed on imaging	SFT lacks psammoma bodies; immunohistochemistry is CD34-positive and EMA-negative (opposite of meningioma); higher recurrence rate and tendency for extracranial metastasis
Glioblastoma (GBM)	Both present in older adults with headache and focal deficits	GBM is an intra-axial tumor with ring enhancement, central necrosis, and irregular borders crossing the corpus callosum ("butterfly pattern"); meningioma is extra-axial, homogeneously enhancing, well-circumscribed
Lymphoma (CNS)	Both can be dural-based; both enhance homogeneously	Primary CNS lymphoma is typically periventricular and intra-axial; it occurs in immunocompromised patients (HIV/AIDS); enhances homogeneously but is deep-seated, not dural-based with a tail
Epidermoid cyst	Both can occur at the CPA	Epidermoid is non-enhancing, shows restricted diffusion on DWI (bright signal), and does not have a dural base; no calcification or psammoma bodies

6. Traps and High-Yield Pearls

The single most common way students miss meningioma questions is by failing to recognize that the tumor is extra-axial. The exam will describe imaging findings of a well-circumscribed, homogeneously enhancing mass with a broad dural base, and the distractors will include intra-axial tumors like glioblastoma or metastasis. The key is to identify the CSF cleft between the mass and the brain, the dural tail, and the broad-based dural attachment as markers of an extra-axial origin. If you see those three features, the answer is almost certainly meningioma.

A second common trap involves the CPA location. When the vignette describes a CPA mass with hearing loss, many students reflexively choose vestibular schwannoma. However, if the question describes a broad dural base without internal auditory canal widening, the answer is CPA meningioma instead. Always check whether the stem mentions IAC involvement.

Another tested concept is the NF2 association. If the vignette describes a young patient with multiple meningiomas (or a meningioma combined with bilateral vestibular schwannomas), the underlying diagnosis is NF2 (chromosome 22). Do not confuse this with NF1 (chromosome 17), which is associated with optic pathway gliomas and neurofibromas, not meningiomas.

The hormonal link is a favorite for clinical reasoning questions. A pregnant woman with worsening headaches and an enlarging extra-axial mass on MRI should point to meningioma growth driven by progesterone receptor activation. Anti-progestins like mifepristone have been investigated but are not standard therapy; the answer on the exam is conservative management with dexamethasone and postpartum surgical planning unless there is acute deterioration.

Finally, do not confuse psammoma bodies across pathology questions. They appear in meningioma, papillary thyroid carcinoma, serous papillary ovarian carcinoma, and mesothelioma. The exam tests whether you can match the histological finding to the correct clinical context.

The core competency being tested is the ability to localize a lesion as extra-axial based on imaging descriptors, connect the demographic profile (older female) and histological hallmarks (psammoma bodies, whorled pattern) to the diagnosis, and sequence management correctly: observation for incidental findings, surgery for symptomatic disease, and radiation for residual or high-grade tumors.

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