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Brown syndrome was first characterised in 1950 by Harold Whaley Brown as a restrictive limitation to elevation in adduction.1 On the basis of surgical findings Brown implicated a shortened superior oblique (SO) tendon sheath as the cause of this syndrome. Most subsequent reports have alternatively proposed an abnormality in the trochlear-SO tendon complex as the cause of restriction to elevation in adduction. Although various causes of acquired Brown syndrome have been described, its association with ethmoidal mucocele is very rare.
A 38 year old man noted sudden onset of binocular vertical diplopia appreciable in levoversion and relieved with chin-up position. There was no history of trauma or any medical illness.
Uncorrected visual acuity was 20/20 in both eyes. A soft compressible tender mass measuring 2×2 cm on the superonasal aspect of the right upper lid extending from the trochlea to the medial canthal tendon was noted. Motility examination showed underelevation in adduction of the right eye mimicking Brown syndrome (fig 1). A right hypotropia of 2Δ in primary gaze increasing to 4Δ in left and upgaze was present.
Contrast magnetic resonance imaging (MRI) (fig 2) revealed an expansile non-enhancing 3–4 cm mass of the right ethmoidal sinus having an intraorbital extraconal extension consistent with a mucocele. The mass appeared to be pressing on the globe causing effacement of the right medial rectus and superior oblique tendon with anterolateral displacement of the trochlea. Endoscopic removal of the mass with subsequent pathology confirmed the diagnosis of mucocele. Following endoscopic removal the patient was asymptomatic for diplopia. Upgaze ability in adduction was improved, but still moderately limited.
Various aetiologies of acquired Brown syndrome have been described such as frontal sinus surgery,2 blepharoplasty,3 chronic sinusitis, trauma, inflammatory,4 systemic lupus erythematosis,5 and restrictive fibrous bands. An isolated case of acquired Brown syndrome caused by a fronto-ethmoidal mucocele has been reported.6 High resolution MRI demonstrated varied abnormalities in both congenital and acquired Brown syndrome such as traumatic or iatrogenic scarring, avulsion of the trochlea, cyst in the superior oblique tendon, inferior displacement of the lateral rectus pulley, and fibrous restrictive bands extending from the trochlea to the globe.7
According to the anatomic abnormalities noted by MRI, four distinct mechanisms of Brown syndrome were identified: trochlear damage, SO tendon abnormalities, abnormalities of rectus extraocular muscle pulleys, and congenital abnormalities of SO muscle.7 MRI can define the pathological anatomical abnormalities causing Brown syndrome, thereby individualising surgical management without reliance on extensive exploratory surgery.
Competing interests: none declared
ALR is a recipient of a Research to Prevent Blindness Physician-Scientist Merit Award.