Fibrous dysplasia of sphenoid wing with secondary aneurysmal bone cyst: a rare case report

An aneurysmal bone cyst is a locally destructive benign lesion affecting mostly the long bones. Aneurysmal bone cyst of the skull bones is a very rare phenomenon and the involvement of the sphenoid bone of the skull with extension into the orbit is even rarer. We present a case of 15-year-old adolescent with fibrous dysplasia of the sphenoid wing with secondary aneurysmal bone cyst. A 15-year-old male presented to us with chief complaints of headache with swelling in the left temporal region of the face and proptosis of the left eye associated with decreased vision for the past 2 months. NCCT showed a large heterogeneous mass in the left temporal region extending into left orbit. Gadolinium-enhanced MRI showed a well-defined multiloculated osteo-expansile lesion in the left middle cranial fossa extending into the anterior cranial fossa consistent with the fibrous dysplasia of the sphenoid bone with associated aneurysmal bone cyst. Digital subtraction angiography brain to look for any feeders to the lesion was done followed by microsurgical gross total excision of the tumor. The histopathology report confirmed it to be fibrous dysplasia secondary to aneurysmal bone cyst. Aneurysmal bone cyst is a rare entity, commonly affecting the long bones of the body. The involvement of sphenoid wing of skull is very rare occurrence. It can be primary or secondary to fibrous dysplasia, chondroblastoma, giant cell tumor, fibromyomas, etc. Fibrous dysplasia with secondary aneurysmal bone cyst should be kept in mind as one of the differential diagnoses while dealing with osteolytic bone lesions of skull.