Case of the Week

Background:

• Aspergillosis is a fungal infection caused by ubiquitous fungi of Aspergillus species. An aspergilloma is a noninvasive type of aspergillosis and a fungus ball composed of Aspergillus hyphae along with cellular debris and mucus.
• Clival aspergilloma is a rare life-threatening disease that occurs mainly via direct spread from the adjacent paranasal sinuses. Its dissemination to the brain results in an extremely high mortality rate (85–100%). Although the clinical diagnosis is challenging due to its rarity and nonspecific symptoms, prompt, accurate diagnosis is crucial for appropriate treatment.

Clinical Presentation:

• Patients may be asymptomatic or have nonspecific symptoms such as headaches. As the lesion enlarges, location-dependent neurologic symptoms such as abducens nerve palsy can develop and worsen.

Key Diagnostic Features:

• CT findings often can be nonspecific but demonstrate changes in adjacent structures including paranasal sinusitis and bony destruction.
• Signal intensity on T2WI is the key to distinguishing clival lesions. Hypointensity on a hyperintense background on T2WI is characteristic of aspergilloma and represents paramagnetic elements that are essential for the growth of Aspergillus hyphae. The findings correspond to a hyperdense area seen on CT. The patterns of contrast enhancement correlate with the immunocompetence level and are various (ring, solid, heterogeneous, or homogeneous). Fungal masses have no contrast effect.
• Confirmation of Aspergillus species in histopathologic examination (Grocott methenamine silver stain) and culture clinches the diagnosis.

Differential Diagnoses:

• Differentials include bone-destructive midline clival lesions.
• Chordomas: These are slow-growing malignant bone neoplasms arising from the remnants of the embryologic notochord. Clivus is the most common location in the skull base chordomas. These show as very hyperintense on T2WI and heterogeneously enhance on contrast-enhanced T1WI.
• Aneurysmal bone cysts: These are benign bone tumors commonly found in long bones of childhood and adolescence. Clivus is an unusual location for these. These appear to have fluid-fluid levels representing areas of the blood of variable age on MRI.
• Solitary bone plasmacytomas: These arise from neoplastic monoclonal plasma cells localized in the bone marrow and most commonly involve vertebrae. The skull base including clivus is a rare location for these. These show curvilinear hypointense areas within hyperintense backgrounds on T2WI (the “mini-brain” sign).
• Metastases: Although clival metastases are extremely rare, these can occur in the context of a known history of a distant malignancy.

Treatment:

• Surgical resection with wide drainage with/without adjuvant antifungal pharmacotherapy