Pendred syndrome comprises the association of severe congenital sensorineural 
deafness with thyroid pathology. Although it is the commonest form of syndromic 
hearing loss, the primary genetic defect remains unknown. The variable clinical 
presentation allied to the difficulty in securing the diagnosis have resulted in 
relatively poor documentation of the radiological features of this syndrome. We 
now present data on 40 patients, all complying with strict diagnostic criteria 
for the disorder, and describe our experience of the prevalence of specific 
malformations of the inner ear as well as comparing the relative merits of 
computed tomography (CT) and magnetic resonance imaging (MRI) in the 
investigation of this inherited condition. Deficiency of the interscalar septum 
in the distal coils of the cochlea (Mondini deformity) was found to be a common 
but probably not a constant feature of Pendred syndrome. However, enlargement of 
the endolymphatic sac and duct in association with a large vestibular aqueduct 
was present in all 20 patients examined by MRI. We conclude that thin section 
high resolution MRI on a T2 protocol in the axial and sagittal planes is the 
imaging investigation of choice.