AIMS: Our aim was to elucidate the etiology of Brown syndrome by evaluating the 
trochlea position, morphologic characteristics of the extraocular muscles 
including superior oblique muscle/tendon complex, and the presence of the 
cranial nerves (CN) III, IV, and VI using magnetic resonance imaging (MRI) in 
eight patients with unilateral congenital Brown syndrome and one patient with 
bilateral congenital Brown syndrome.
METHODS: Nine consecutive patients diagnosed with congenital Brown syndrome had 
a comprehensive ocular examination and MRI for the CN III, CN VI, and the 
extraocular muscles. Five of the nine patients underwent additional high 
resolution MRI for CN IV. The distance from the annulus of Zinn to the trochlea 
was measured.
RESULTS: Normal sized CN III, IV, and VI, as well as all extraocular muscles, 
could be identified bilaterally in all patients with available MRI. The distance 
from the annulus of Zinn to the trochlea was the same in both eyes.
CONCLUSIONS: The findings for our patients, particularly in those who underwent 
additional high resolution MRI, did not provide evidence of a lack of CN IV as a 
cause of Brown syndrome.