giovedì 12 marzo 2009
Axial T1 fat-saturated MRI of the internal auditory canal (precontrast) shows acute hemorrhage with hyperintensity in the cochlea and vestibule.
Diagnosis: Intralabyrinthine hemorrhage
Sudden hearing loss secondary to an acute cochlear hemorrhage is rare. Estimates of annual incidence of sudden hearing loss are 5-20 per 100,000 of which only a small percentage is due to intralabyrinthine hemorrhage. Only 1-4% of all cases of sudden sensorineural hearing loss are bilateral. The fact that this patient has Down syndrome is significant, since hearing loss has been reported in both acute and chronic myeloid leukemias, which occurs at a higher frequency in Down patients. One theory proposes that hyperleukocytosis causes leukostasis with abnormal microvascular perfusion. The cochlea is an end organ in terms of its blood supply with no collaterals. It is supplied by the labyrinthine artery, a branch of AICA. Its tortuous course predisposes it to the effects of hyperviscocity. In addition, it is extremely sensitive to changes in blood supply. Thus, the time course of hearing loss correlates well with a vascular event such that an acute hearing loss is most likely caused by hemorrhage, thrombosis, embolism or hypotension. This patient should be evaluated for an underlying leukemia.
Imaging can be used as an adjunct in both conductive and sensorineural hearing loss. CT imaging is more sensitive for conductive hearing loss while MR is more sensitive for sensorineural hearing loss. Fluid in the labyrinth is normally isointense with CSF. In the acute phase of hemorrhage, hypointense signal can be seen on T2-weighted images, while hyperintense T1 signal can be seen for up to 6 months because of the extended life span of the erythrocytes in the perilymph. Other possible causes of sensorineural hearing loss that can be seen on MR include vestibular schwannomas, arachnoid cysts, multiple sclerosis, and inflammation.