Meningioma

Detailed Overview

Meningiomas are the most common primary intracranial tumors in adults, accounting for over 30% of cases. Because they grow slowly inward from the meninges, they do not invade the brain parenchyma but rather compress it. Many are discovered incidentally on imaging and remain asymptomatic. When symptoms do occur, they are insidious and depend entirely on the tumors location (e.g., frontal lobe compression causing personality changes, optic nerve compression causing vision loss). While >80% are benign (WHO Grade 1), their location can make surgical removal challenging. Complete resection is often curative.

Epidemiology & Demographics

Incidence increases with age, peaking in the 6th and 7th decades. They are approximately twice as common in women as in men, likely due to hormone receptor expression. More common in African Americans.

Etiological Mechanism

Most are sporadic, driven by somatic mutations, most frequently the loss of the NF2 tumor suppressor gene on chromosome 22q. Prior ionizing radiation to the head is a strong environmental trigger.

Primary Causes

Genetic mutations in arachnoid cap cells. Can be induced by prior therapeutic radiation (e.g., for childhood leukemia or tinea capitis).

• Prior Radiation Therapy: High-dose radiation to the skull increases risk significantly, often presenting 10-20 years later.
• Female Sex / Hormones: Growth may accelerate during pregnancy due to progesterone receptors on the tumor.
• Neurofibromatosis Type 2 (NF2): Genetic syndrome causing multiple inherited meningiomas and bilateral vestibular schwannomas.

Arachnoid cap cells, located in the arachnoid villi, undergo neoplastic transformation following chromosomal deletions (notably 22q loss). The tumor grows slowly, firmly attached to the dura mater (causing a dural tail on MRI). It forms a well-circumscribed, lobulated mass that pushes the underlying brain tissue, inciting reactive vasogenic edema in the white matter. Histologically, they show a whorled pattern of spindle cells and calcified concentric concretions called psammoma bodies. They can invade the adjacent skull bone, causing hyperostosis, but rarely break the pia mater to invade the brain.

Characteristic Clinical Presentation

• Headache: Worse in the morning or with coughing/straining (indicates raised intracranial pressure).
• Focal Seizures: Common if the tumor is over the cerebral convexities or parasagittal regions.
• Anosmia: Loss of smell (seen in olfactory groove meningiomas).
• Vision Changes: Visual field deficits or proptosis (seen in sphenoid wing or optic nerve sheath meningiomas).

Physical Examination Signs

• Focal motor weakness or hyperreflexia (compression of motor cortex).
• Papilledema on fundoscopic exam (sign of elevated ICP).
• Cranial nerve palsies (e.g., CN III, IV, VI if located in the cavernous sinus).

• Vasogenic Brain Edema: Severe swelling surrounding the tumor causing neurological deficits.
• Hydrocephalus: Obstruction of CSF flow if the tumor compresses the ventricular system.
• Surgical Morbidity: Cranial nerve damage or stroke from sacrificing encased blood vessels during surgery.

Diagnostic Criteria & Guidelines

Diagnosis is strongly suspected based on characteristic MRI findings (homogeneously enhancing extra-axial mass with a dural tail) and confirmed by histopathological examination following resection or biopsy.

Differential Diagnosis

• Dural metastasis (e.g., from breast or prostate cancer)
• Hemangiopericytoma
• Schwannoma (if in the cerebellopontine angle)
• Glioblastoma (usually intra-axial, not dural-based)

Laboratory Tests & Biomarkers

• Not applicable: No specific blood tests diagnose meningioma. Pre-op labs are standard surgical workup.

Imaging Modalities & Findings

• MRI Brain with Gadolinium:
• CT Head Without Contrast:

• WHO Grade 1
  Benign, slow-growing, low mitotic activity (80% of cases).
• WHO Grade 2 (Atypical)
  Increased mitotic figures, brain invasion, or specific aggressive histologic subtypes; higher recurrence rate (15%).
• WHO Grade 3 (Anaplastic)
  Malignant, highly aggressive, rapid growth, resembles carcinoma/sarcoma (<5%).

Second-Line & Adjunctive Therapy

Stereotactic Radiosurgery (e.g., Gamma Knife) is used for small, symptomatic tumors in deep, surgically inaccessible areas (e.g., cavernous sinus), or for remnants left behind after surgery.

Surgical & Procedural Management

Craniotomy and tumor resection. The goal is complete removal of the tumor, its dural attachment, and any involved bone (Simpson Grade I), though functional preservation takes priority over complete resection near eloquent brain areas.

Recommended Lifestyle Changes

• Avoidance of exogenous hormones/oral contraceptives if possible, as they may stimulate tumor growth.
• Seizure precautions (no driving) if presenting with epilepsy until cleared by neurology.

Patient Counseling & Advice

Provide reassurance that "brain tumor" in this context usually means a benign, curable growth, not cancer. Explain that even benign tumors can cause serious damage if they press on vital structures, making surgery necessary.

Follow-Up & Monitoring Schedule

Post-operative MRI at 3 months, then annually for 5 years, then every 2-3 years, as late recurrences can happen even 10 years out.

Preventive Strategies

Avoidance of unnecessary ionizing radiation to the head.

Excellent for fully resected WHO Grade 1 tumors (10-year survival >90%). Atypical and Anaplastic grades have higher recurrence rates and lower survival.