Middle cranial fossa tumor presenting as chronic otitis media: Rare case of aneurysmal bone cyst

INTRODUCTION: Aneurysmal bone cysts (ABCs) are a rare, vascular, rapidly growing, benign, osteolytic lesions. Most ABCs involve the metaphysis of long bones, vertebrae, or flat bones. In this study, we review the literature to better understand the natural history, clinical presentation, and treatments. PRESENTATION OF CASE: A 34-year-old man who presented with left intermittent otorrhea for months. Yellowish, pus-like discharge was noted. Mild tinnitus, hearing loss, and occasional headache was also found. The initial impression was chronic otitis media and ear drops were prescribed. However, his symptoms did not improve in the following months. The brain MRI with gadolinium enhancement revealed an extra-axial mixed signal intensity lesion on the T2-weighted image, multiloculated cystic components and rim enhancement was noted over the left middle cranial fossa. Left fronto-temporal craniotomy for tumor removal was performed. The pathological reports revealed an aneurysmal bone cyst. CLINICAL DISCUSSION: Typically, ABCs present with localized swelling and pain due to their rapid growth and expansion, with concomitant signs corresponding with the anatomical location of the lesion. MRI studies can reveal the cystic components of the lesion and multiple fluid levels within multiloculated cysts resulting from unclotted blood, separated from the soft tissue and medullary bone. Histopathologic diagnosis of ABC is the presence of multiple blood-filled cystic spaces separated by fibrous septa. The fibrous septa are composed of spindle-celled fibroconnective tissue with occasional osteoclast-type giant cells. CONCLUSION: ABCs are a rare, osteolytic lesions that rarely involve the skull. When the MRI shows a lesion with soap-bubble appearance in the calvaria, an aneurysmal bone cyst should be considered in the differential diagnosis, even if it is an extremely rare entity or the patient is relatively old. Surgical resection of the tumor is the first choice for treatment.