Computed tomography scan to diagnose abducens nerve palsy cases with superior-compartment atrophy.

Purpose: To use orbital computed tomography (CT) to explore the proportion of superior-compartment lateral rectus muscle atrophy in abducens nerve palsy and its relationship with clinical findings.

Methods: Twenty-two patients with isolated unilateral abducens nerve palsy were enrolled. Orbital CT scans of all patients were acquired. All measurements were performed in two ways for normal and paretic lateral rectus muscles: posterior volume (mm) and maximal cross-section area (mm). These variables were also measured separately in the superior and inferior 40% of the muscle. Primary position esotropia and amount of abduction limitation was also recorded.

Results: The mean deviation was 23.4 ± 12.1 (range, 0-50); the mean limitation of abduction, -2.7 ± 1.3 (range, -1 to -5). Seven cases (31.8%) showed the gross morphologic characteristics of superior-compartment atrophy. In these 7 cases, the mean percentage of atrophy in posterior volume and in maximal cross-section was significantly greater in the superior compartment than the inferior compartment (P = 0.02 for both). The mean limitation of abduction in these 7 cases (-1.7 ± 0.9; range, -1 to -3) was significantly lower than in other cases (-3.1 ± 1.3, range, -1 to -5 [P = 0.02]).

Conclusions: In our study cohort, a subgroup of abducens nerve palsy cases demonstrated evidence of superior portion lateral rectus atrophy on orbital CT. The superior-compartment-atrophy group had both a smaller primary gaze esotropia and a smaller abduction deficit, providing evidence that compartmental atrophy should be considered in patients with partially retained lateral rectus function.