Meningioma

01Pathophysiology

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.

02Classification and Clinical Manifestation

WHO Grading

By Location

03Diagnostic Workup

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.

04Management and Treatment

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:

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 ($\le 3\backslash leq\; 3$ 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.

05Differential Diagnosis and Distractors

06Traps 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.