What is an intracranial inflammatory mass in a middle-aged to elderly adult patient?

Intracranial Inflammatory Mass: Definition and Clinical Approach

An intracranial inflammatory mass is a non-neoplastic, tumor-like lesion composed of polyclonal inflammatory cells—predominantly mature plasma cells and lymphocytes—that mimics a brain tumor clinically and radiologically but represents a reactive inflammatory process rather than a malignancy. 1, 2

Pathological Characteristics

Inflammatory pseudotumor (also called plasma cell granuloma) is the most common type of intracranial inflammatory mass and consists of:

• Sheets of mature plasma cells and lymphocytes with germinal center formation, confirmed by immunohistochemical studies showing polyclonal (not monoclonal) cell populations 1, 2
• Dense fibrotic tissue heavily infiltrated with chronic inflammatory cells, distinguishing it from plasma cell neoplasms like plasmacytoma or lymphoma 1, 3
• Adjacent cortical changes including lymphoplasmocytic inflammation, neuronal loss, reactive gliosis, and occasionally disturbed cortical lamination in neighboring brain tissue 3

Clinical Presentation in Middle-Aged to Elderly Adults

These lesions present with symptoms indistinguishable from brain tumors:

• Seizures (partial motor seizures, generalized seizures) are the most common presenting symptom 2, 3
• Focal neurological deficits including weakness, aphasia, or cranial neuropathies depending on location 4, 2
• Headaches and altered mental status 2
• Progressive symptoms over months to years if untreated 4

Radiological Features

On imaging, these masses are virtually indistinguishable from meningiomas or malignant gliomas:

• Well-demarcated, enhancing masses on contrast CT or MRI that appear as sharply circumscribed lesions 1, 2
• Dural-based lesions that can extend into brain parenchyma, mimicking meningioma 1, 3
• Ill-defined, heterogeneously enhancing lesions in deep structures (basal ganglia, insula) that may suggest high-grade glioma 2, 5
• Mass effect with surrounding edema 2

Differential Diagnosis Considerations

The critical differential includes:

• Meningioma (most common clinical misdiagnosis for dural-based inflammatory masses) 1, 3
• High-grade glioma (for parenchymal lesions with heterogeneous enhancement) 2
• Lymphoma (must be excluded via immunohistochemistry showing polyclonal B and T cells) 4, 2
• Infectious processes including parasitic disease (cerebral sparganosis in patients from endemic areas like Asia) 5
• Plasma cell neoplasms (plasmacytoma—excluded by demonstrating polyclonal rather than monoclonal plasma cells) 1, 2

Diagnostic Workup

Definitive diagnosis requires tissue sampling because imaging cannot reliably distinguish inflammatory masses from neoplasms:

• Surgical biopsy or resection is mandatory for histopathological diagnosis 1, 4, 2
• Immunohistochemical staining for B and T cell markers to confirm polyclonal population and exclude lymphoma 4, 2
• Extensive cultures and special stains to identify any infectious etiology (bacterial, fungal, parasitic) 4, 5
• Electron microscopy may be helpful in difficult cases 3

Management Strategy

Complete surgical excision is the treatment of choice and appears curative:

• Total resection should be attempted when feasible and safe, as it provides both diagnosis and definitive treatment 2, 3
• Stereotactic biopsy is appropriate for deep or eloquent location lesions where resection carries high risk 2
• Corticosteroids may be used as adjuvant therapy, though response is variable and not always effective 4, 2
• Radiation therapy should be considered for lesions where complete resection is not possible or for progressive disease unresponsive to steroids 4, 2

Critical Pitfalls to Avoid

Do not assume a well-circumscribed, enhancing intracranial mass is necessarily a meningioma—inflammatory pseudotumor must be in the differential, particularly in middle-aged adults with atypical features 1

Do not rely on imaging alone for diagnosis, as these lesions are radiologically indistinguishable from true neoplasms 1, 2

Do not mistake polyclonal plasma cell infiltration for plasmacytoma—immunohistochemistry demonstrating polyclonality is essential to avoid misdiagnosis and inappropriate treatment 1, 2

Consider travel history to endemic areas when evaluating inflammatory masses, as parasitic infections like sparganosis can produce identical clinical and radiological presentations 5

Prognosis

The natural history is incompletely understood, but complete surgical excision appears curative with excellent long-term outcomes 2, 3. Progressive disease despite steroid therapy warrants consideration of radiation therapy 4.