Double globes in single-orbit sign

A 19-year-old man presented with complaints of outward displacement of the left eyeball for the past 2 years. On examination, the left eyeball had lateral dystopia of 6 mm. On T2-weighted MRI, a well-defined cystic lesion in the left orbit, resembling the other globe, was seen (Fig. 1). CT scan revealed a heterogeneous lesion in the left fronto-ethmoid sinus with extension into the orbit. A provisional diagnosis of left fronto-ethmoidal mucocoele was made. He underwent surgical removal of the mucocoele, and the affected ethmoid sinus was connected to the nasal cavity.

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FIG 1.

MRI showing a hyperintense cystic lesion on T2-weighted imaging at the left medial canthus, giving the appearance of ‘the double globe in single-orbit’ or ‘the third eyeball’ sign

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Mucocoeles are epithelial-lined cystic lesions frequently located in the paranasal sinuses. Their pathogenesis remains a mystery and many believe the cause to be a sequelae of obstruction of the affected sinus due to chronic rhinosinusitis, trauma or surgery.¹ The presenting symptoms usually include headache, recurrent episodes of nasal obstruction, diplopia, displacement of the ocular globe and in severe instances, meningitis.² Mucocoeles in the fronto-ethmoid sinus displace the eyeball forwards, downwards and laterally. The investigation of choice is CT scan, as it provides details of the bony erosions and orbital and intracranial extensions. On T2-weighted MRI, these appear as well-defined cystic lesions and can mimic the globe, giving the appearance of double globes in a single orbit.³ Malignant lesions, dermoid cysts, fungal and tubercular granulomas and cholesterol granulomas form the list of differential diagnoses. The management of fronto-ethmoidal mucocoeles primarily involves surgical excision with marsupialization.⁴