A rare isolated malformation was detected in a 38-year-old man who was admitted for evaluation of vertigo and dizziness.
A 38-year-old man presented with complaints of vertigo and imbalance for the past 2 years. The patient was admitted for further investigations. On evaluation, moderate bilateral sensorineural hearing loss was noticed.
Magnetic resonance imaging was performed, which revealed bilateral isolated aplasia of the lateral semicircular canals, as shown in the image above. No pathological contrast enhancement was detected. Superior and posterior semicircular canals and cochlea were normal bilaterally. The rest of the findings were normal on MRI. The internal auditory canal and the cerebellopontine angle were normal.
What are semicircular canals?
Semicircular canals of the bony labyrinth in the inner ear are fluid-filled tubes with tiny hair lining the canal. They have a function of sensing the head rotations, specifically the angular accelerations. The information of the head movements is essential for maintaining balance and coordination. There are three semicircular canals: anterior (superior), posterior, and lateral (horizontal). Each is placed at a right angle to the other.
The anterior or superior semicircular canals detect head movements around the lateral axis, the posterior semicircular canals detect head rotation around the sagittal or the anterior-posterior axis, and the lateral canals are for movements around the vertical axis (around the neck)
Isolated malformations of the semicircular canals are a rare find. Usually, these malformations are associated with syndromes or vestibular and cochlear malformations. The structural anomalies may not be detected on the imaging, but the patients may present with clinical features and functional signs of global cochlear, semicircular canal, and otolithic lesions.
In patients with isolated semicircular canal aplasia, it is imperative to investigate further to exclude extensive labyrinthine lesions, even if the aplasia was found incidentally.
Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. The Semicircular Canals. Available from: https://www.ncbi.nlm.nih.gov/books/NBK10863/
Arslan S, Erdogan H, Durmaz MS, Arslan FZ, Oncu F, et al. (2018) Bilateral Isolated Lateral Semicircular Canals Aplasia: MRI Findings. Clin Med Img Lib 4:116. doi.org/10.23937/2474-3682/1510116