Q. What is an intracranial fungal granuloma?

It is a localized chronic granulomatous infection of the brain or meninges caused by fungal organisms. The lesion forms due to a delayed hypersensitivity response with central necrosis and peripheral granulomatous reaction, often mimicking tuberculoma or neoplasm. It may involve brain parenchyma, meninges, or skull base, and is usually secondary to contiguous spread from paranasal sinuses.

Q. What is its epidemiology and incidence?
 

Intracranial fungal granulomas are more common in tropical and subtropical regions such as South and Southeast Asia.
They typically occur in immunocompromised patients, i.e. those with diabetes mellitus, prolonged corticosteroid use, HIV/AIDS, malignancy, or chemotherapy.
 

The most frequent organisms are Aspergillus species and Mucorales (Mucor, Rhizopus). CNS involvement is seen in about 10–20% of disseminated fungal infections. Rarely, fungal granulomas can occur in immunocompetent individuals, especially after chronic sinusitis.

Q. What are the causative organisms and pathological features?
 

A. Pathogenic fungi (can infect immunocompetent hosts):
- Cryptococcus neoformans
- Histoplasma capsulatum
- Coccidioides immitis
- Blastomyces dermatitidis
- Paracoccidioides brasiliensis
- Sporothrix schenckii

B. Opportunistic fungi (in immunocompromised hosts):
- Aspergillus fumigatus, A. flavus, A. niger
- Mucorales: Mucor, Rhizopus, Absidia
- Candida albicans
- Phaeohyphomycosis (dematiaceous fungi)

Histopathology:
 

Granulomatous inflammation with central necrosis, epithelioid and giant cells, and fungal hyphae visible on PAS or GMS stain.
Aspergillus shows acute-angle (45°), septate branching hyphae with angioinvasion and thrombosis.
Mucor shows broad, non-septate right-angle branching hyphae.
Angioinvasion leads to infarction, hemorrhage, and necrosis.

Q. Which sites are commonly affected?
 

- Frontal and temporal lobes by extension from paranasal sinuses (especially sphenoid and ethmoid).
- Cavernous sinus, orbit, and skull base.
- Cerebellum in hematogenous spread.
- Basal cisterns and vascular structures are frequently invaded by Aspergillus.
- Rhinocerebral mucormycosis often begins in nasal cavity and spreads via ethmoid sinuses into the orbit and frontal lobe.

Q. What are the usual clinical features?
 

- Persistent headache and vomiting due to raised intracranial pressure.
- Focal deficits depending on site: hemiparesis, aphasia, cranial nerve palsy.
- Seizures, altered sensorium, or proptosis in cases with orbital extension.
- Cavernous sinus involvement causes ophthalmoplegia, ptosis, and facial numbness.
- Often presents as a space-occupying lesion unresponsive to antibiotics or anti-tuberculous therapy.
- Systemic features include fever, sinus discharge, or signs of chronic sinusitis.

Q. What are the characteristic radiologic features?
 

CT Scan:
- Iso- to hyperdense lesion with irregular margins and surrounding edema.
- May show calcifications or bone erosion in skull base involvement.
- Variable ring or nodular enhancement after contrast.

MRI:
- T1: Iso- to hypointense core.
- T2: Marked hypointensity due to iron and manganese within fungal elements.
- Post-contrast: Peripheral or irregular ring enhancement.
- DWI: May show restricted diffusion when abscess is present.
- MR Spectroscopy: Lipid–lactate peaks with absent amino acid peaks (helps differentiate from pyogenic abscess).
- Sinus disease and orbital or vascular invasion are often visible.
T2 hypointensity with irregular ring enhancement is a characteristic feature of fungal granuloma.

 

MR Angiography/CT Angiography: Essential to evaluate vascular encasement, arterial occlusion, or mycotic pseudoaneurysm formation (due to fungal angioinvasion).

Q. What are the important differential diagnoses?
 

- Tuberculoma
- Pyogenic brain abscess
- Neurocysticercosis (granular–nodular stage)
- High-grade glioma or metastasis
- Sarcoidosis or parasitic granuloma

 

Q. How will you manage a case of intracranial fungal granuloma?

A. Preoperative work-up:
- MRI brain with contrast ± MR angiography
- CT paranasal sinuses to identify the primary source
- Nasal endoscopy for diagnostic biopsy
- Routine hematologic tests and glycemic control
- Fungal culture, KOH mount, and histopathologic confirmation via nasal biopsy if sinus involvement is present

- Systemic Optimization: Urgent glycemic control (HbA1c/blood sugar), reversal of ketoacidosis, reduction of systemic steroids/immunosuppression, and baseline renal/hepatic profiling

B. Surgical Management

Indications:
- Space-occupying lesion with mass effect.
- Diagnostic uncertainty.
- Failure of medical therapy or presence of abscess cavity.

C. Surgical Goals:
Achieve maximum safe resection and decompression.
Obtain specimen for diagnosis.
Control primary source if sinus or skull base involvement exists.

D. Surgical Corridors:

Anterior Skull Base / Cavernous Sinus: Frontotemporal, subfrontal, or cranio-orbitozygomatic (COZ) approach; or expanded endoscopic endonasal approach (EEA) for midline clival/sphenoid lesions.

 

Posterior Fossa: Retrosigmoid or far-lateral approach depending on location.

 

E. Operative Strategy & Pitfalls:

 

Firm & Adherent Lesion: Granulomas are notoriously avascular/fibrotic center-wise but extremely adherent peripherally.

 

Avoid Radical Capsule Traction: Fungi are highly angioinvasive. Encased major arteries (e.g., ICA, MCA, ACoA) become brittle and prone to intraoperative avulsion or postoperative stroke. Perform piecemeal internal debulking rather than en bloc resection when major vessels are involved.

 

Irrigation: Copious irrigation with warm normal saline. Note: Intrathecal or local intraoperative Amphotericin B irrigation is controversial and generally avoided due to chemical arachnoiditis/neurotoxicity risks.

 

Closure: Watertight dural repair (graft if needed) to prevent CSF leak and secondary bacterial meningitis.

Postoperative Care:
- Early initiation of systemic antifungal therapy.
- Monitor renal and hepatic function regularly.
- Control diabetes and immune suppression.

Medical Therapy:
General Principles:
- Start systemic antifungal therapy immediately after diagnosis or biopsy.
- Continue for at least 6–12 weeks or until complete clinical and radiological resolution.
- Choose antifungal according to causative organism, site, and host immune status.

1. Aspergillosis (CNS Aspergilloma / Granuloma)
- First-line drug: Voriconazole
- Loading: 6 mg/kg IV every 12 h for 2 doses.
- Maintenance: 4 mg/kg IV every 12 h or 200 mg PO q12 h.
- Duration: Minimum 6–12 weeks (oral continuation up to 3–6 months).
- Alternative: Liposomal Amphotericin B 3–5 mg/kg/day IV.
- Resistant cases: Posaconazole 300 mg PO daily (after 300 mg BID on day 1) or Caspofungin 50 mg IV daily as adjunct.
- Adjunctive therapy: Endoscopic sinus clearance if paranasal source present.

2. Mucormycosis (Rhinocerebral / Skull Base Form)
- First-line: Liposomal Amphotericin B 5–10 mg/kg/day IV.
- Conventional Amphotericin B deoxycholate 1 mg/kg/day if liposomal not available.
- Step-down / maintenance:
- Posaconazole 300 mg PO daily (after 300 mg BID day 1)
- or Isavuconazole 200 mg IV/PO TDS for 48 h, then 200 mg daily.
- Duration: At least 12 weeks; longer if sinus invasion persists.
- Adjuncts: Surgical debridement of necrotic tissue, control of diabetes, cessation of steroids, and correction of acidosis.

3. Candida (Cerebral Candidiasis / Abscess)
- First-line: Liposomal Amphotericin B 5 mg/kg/day IV ± Flucytosine 25 mg/kg q6 h PO.
- Step-down: Fluconazole 400–800 mg/day PO or IV once improved.
- Duration: 6–8 weeks minimum. Drain large or multiloculated abscesses surgically.

4. Cryptococcus (Cryptococcal Meningoencephalitis / Granuloma)
- Induction (2 weeks): Amphotericin B 1 mg/kg/day + Flucytosine 25 mg/kg q6 h.
- Consolidation: Fluconazole 400–800 mg/day PO for 8 weeks.
- Maintenance: Fluconazole 200 mg/day PO for 6–12 months, especially in HIV-positive patients.
- Adjunct: Manage raised ICP by CSF drainage if needed.

5. Dematiaceous (Phaeohyphomycosis and other rare fungi)
- Voriconazole 200 mg PO q12 h or Posaconazole 300 mg PO daily preferred.
- Duration: ≥ 6 months, often prolonged due to frequent relapse.

Monitoring and Supportive Care:
- Check renal and hepatic functions twice weekly during amphotericin therapy.
- Maintain serum potassium > 3.5 mmol/L and magnesium > 1.8 mg/dL.
- Avoid concomitant nephrotoxic drugs.
- Monitor drug levels for voriconazole (trough 1–5 µg/mL).
- Control underlying systemic disease (diabetes, immunosuppression).

Q. What are the possible complications?
 

- Postoperative hemorrhage or infarction from angioinvasion.
- Meningitis or CSF leak.
- Hydrocephalus.
- Renal toxicity from amphotericin.
- Recurrent infection from untreated sinus or orbital focus.

Q. What is the prognosis?
 

Mortality remains high, ranging from 25–40% in angioinvasive aspergillosis and mucormycosis.
Favorable prognosis depends on:
- Early diagnosis and prompt initiation of antifungal therapy.
- Complete surgical excision where feasible.
- Control of systemic risk factors.
- Immunocompetent status of the patient.

Q. What is the follow-up protocol?
 

- MRI brain every 3 months during the first year, then every 6 months.
- Monitor renal and hepatic parameters during therapy.
- Repeat sinus evaluation to rule out recurrent infection.
- Long-term oral antifungal prophylaxis in persistent immunocompromise.

Recalls:
- Most common agents: Aspergillus and Mucor.
- Classic MRI finding: T2 hypointense core with irregular ring enhancement.
- Confirm diagnosis by biopsy before starting therapy.
- Voriconazole is the drug of choice for CNS aspergillosis.
- Liposomal Amphotericin B (5–10 mg/kg/day) is preferred for mucormycosis.
- Combined surgery and antifungal therapy give the best outcomes.
- Early sinus debridement prevents recurrence and intracranial extension.