Fungal calvarial infection: A rare presentation

A 15-year-old female presented with complaints of left supraorbital swelling, mild fever and intermittent localized pain for the past three months. She had no history of trauma, vomiting, discharge from swelling, visual or any other neurological deficit. No h/o any comorbidities or immunocompromised state present.

On examination swelling was firm, fluctuant and non-mobile. No e/o any overlying skin changes such as papules, pustules, ulceration or discharge from the swelling seen.

Contrast enhanced CT and MRI brain was done and subsequently USG guided aspiration of the swelling was performed. CECT of the brain shows a well-defined peripherally enhancing collection with subgaleal and epidural component in the left frontal bone. The bone window images demonstrate the involvement of the left frontal bone with thinning and erosion. On contrast enhanced MRI, the collection was T1 hypo to isointense and T2 FLAIR hyperintense showing peripheral enhancement. Underlying left frontal bone shows altered marrow signal intensity with thinning. No other lesions were seen in the rest of the calvaria.

The findings on CT and MRI were consistent with an infective/ granulomatous etiology with possibility of tuberculosis was considered as there was a remote history of contact in family.

USG guided aspiration of the above-mentioned lesion and histopathological evaluation revealed necrotic inflammatory cells and hyphal structures consistent with granulomatous fungal etiology due to Aspergillus species.

Focal infection of the cranial vault can be post-traumatic, post-surgical and rarely due to invasion and is different from the skull base osteomyelitis which usually occurs due to invasion of pathogens from adjacent organs [1]. Calvarial osteomyelitis represents ~1.5% of all osteomyelitis cases with high morbidity and mortality [2].

Other etiologies causing calvarial vault lesions include granulomatous disorders like tuberculosis, sarcoidosis, Churg Strauss, granulomatosis with polyangiitis and Behcet’s disease [3]. A high degree of suspicion is needed to diagnose calvarial infections as numerous systemic malignancies like metastasis, lymphoma, leukaemia, myeloma and histiocytosis lymphoma can have similar presentation [2].

Our patient had a peculiar presentation with insidious onset left supraorbital swelling. She was fairly well preserved other than the swelling. Her lab investigations showed elevated CRP and ESR levels. Blood counts showed leukocytosis with predominant lymphocytes. Her random blood sugar was within normal limits. Due to presence of collection with associated bone changes and lack of solid component and multifocality, we suggested a possibility of infective aetiology.

Fungal calvarial infections are usually secondary to a trauma, extension from adjacent frontal or ear infection, usually in an immunocompromised patient. Diabetes mellitus was found to be the most common risk factor (57%), followed by chronic otitis externa (33%) and underlying chronic sinusitis (29%)[4].  Our patient did not have any of this history or imaging manifestations. Lack of aggressive features like bone destruction, intracranial complications and presence of a well-defined collection suggests an indolent and contained infection rather than an invasive Mucor mycosis

Next set of differentials include multisystemic disorders of granulomatous or neoplastic etiology. These diseases cause multifocal lesions, which on CT can be seen as mass with bone erosion; on MR imaging these lesions are T1 iso to hypointense and T2 hyperintense and may show enhancement[5]. Our case had a single lesion with lack of solid component.

In the appropriate clinical setting, imaging features may strongly suggest granulomatous involvement of calvarial bones, but tissue confirmation is required for definitive diagnosis. As was in our case, tissue examination was performed and yielded a fungal etiology.

In conclusion, fungal infection of the calvarial bones is an unexpected entity in immunocompetent individual without para nasal sinus involvement. As tuberculosis is known to be a great mimicker, fungal infections too can present atypically. Hence a high degree of clinical suspicion followed by tissue sampling and examination ensures accurate diagnosis and timely treatment and recovery.