Presentation
The patient presented with nasal obstruction and mild right-sided proptosis.
Patient Data
A CT study shows a large bone destructing lesion centered in the right ethmoid bone, destroying the right middle turbinate and perpendicular plate of the ethmoid medially. Laterally, it appears to destruct the lamina papyracea, displacing the right medial rectus muscle and causing mild proptosis. Superiorly, the mass is seen eroding the cribriform plate of the ethmoid, partially extending into the anterior cranial fossa. The mass also appears to extend into the right maxillary sinus and obstruct the right frontoethmoidal recess.
An MRI study shows a complex mass with multiple cystic components demonstrating fluid-fluid levels on the T2 sequence, creating an image suggestive of an aneurysmal bone cyst..
Case Discussion
Aneurysmal bone cyst (ABC) is a non-neoplastic lesion composed of blood-filled sinusoidal spaces, which manifest as a bony expansile lesion.
The most common locations for ABCs are the metaphyses of long bones, followed by flat bones. Only 2% are found in the head and neck area, with the mandible and maxilla being the most frequently involved sites. Involvement of the ethmoid sinus (as in this case) is considered an extremely rare occurrence, with only a few reported cases. MRI is helpful in making the diagnosis in the presence of the characteristic finding of multiple cysts with fluid-fluid levels. Although no obvious signs of a fibro-osseous lesion could be identified in the current case, histology confirmed the imaging diagnosis of ABC on top of fibrous dysplasia.
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