1. MRI AND CT EVALUATION OF ACQUIRED SENSORINEURAL HEARING LOSS MARK B JOHNSON MD, JOHN VARVARIKOS MD, HEATHER BURBANK MD, JOSHUA NICKERSON MD. DEPARTMENT OF RADIOLOGY, UNIVERSITY OF VERMONT MEDICAL CENTER, BURLINGTON, VT Contact: mark.johnson@uvmhealth.org Educational Objective: 1.Review the pertinent inner ear and auditory pathway anatomy. 2.Review the pathology of different forms of acquired sensorineural hearing loss as well as their signs and symptoms. 3.Review the MRI and CT characteristics of the various forms of acquired sensorineural hearing loss. Normal Anatomy from the Inner Ear, Internal Acoustic Canal, Vestibulocochlear Nerve, and Neuronal Pathways. Introduction Acquired sensorineural hearing loss (SNHL) is a common problem among both pediatric and adult populations with varied pathologies. Although the majority of acquired SNHL is age related with no relevant imaging findings, numerous other forms of SNHL have unique characteristics on both MRI and CT. SNHL abnormalities may involve the bony labyrinth, membranous labyrinth, vestibulocochlear nerve, extra-axial space, or intra-axial space. Early recognition is paramount, and radiology plays a key role in evaluation and diagnosis, potentially limiting permanent disability. Ramsay Hunt Syndrome Infection due to reactivation of Varicella Zoster in the geniculate ganglia of the facial nerve. Imaging modality: Contrast enhanced T1 MRI. Finding may include enhancement of the external ear, CN7, membranous labyrinth, and facial nucleus within the brainstem. Symptoms: Facial nerve palsy, pain and vesicles of the ear canal, hearing loss, vertigo. Contrast enhanced T1W images reveal subtle enhancement of the labyrinthine segment of the left facial nerve (red arrow). Endolymphatic Sac Tumor Invasive papillary epithelial tumor arising from the endolymphatic sac. Imaging: Permeative destructive lesion on CT. Often increased signal on T1, increased T2 signal of the cystic components, and heterogeneous enhancement. Strong association with von Hippel-Lindau disease. A) Destructive lesion centered over the endolymphatic sac with partial dehiscence of the semicircular canal. B) Increased signal of cystic components on T2W. B B A A Vestibular Schwannoma Benign primary tumor arising from myelin forming Schwann cells surrounding the vestibulocochlear nerve. Imaging: Avidly enhancing on C+ T1W. Microhemorrhage often present on T2 GRE. CP angle mass with an “Ice cream cone” appearance extending from the IAC. Symptoms: Hearing loss, tinnitus, balance disorders, headache. C+ T1W images reveal an enhancing left cerebellopontine angle mass exiting from the left IAC. Otic Capsule-Violating Temporal Bone Fracture Longitudinal fracture: Parallel to the petrous ridge. Typically do not involve the otic capsule. Transverse fracture: Perpendicular to the petrous ridge and may involve the otic capsule. Otic capsule-violating signs/symptoms: CNVII injury, SNHL, CSF leak. CT images reveal a transverse fracture extending through the otic capsule, involving the vestibular aqueduct, vestibule, and facial nerve canal at the geniculate ganglion. Otosclerosis/Otospongiosis Autosomal dominant osteodystrophy of the otic capsule with variable penetrance. Replacement of “ivory-like” endochondral bone with spongy vascular bone. Types: Fenstral and retrofenstral/cochlear. Imaging: Temporal bone CT. Lucency at the oval window which spreads to the bony labyrinth. Signs/symptoms: Progressive disease presenting in the 2-4 th decades with SNHL, conductive hearing loss, or tinnitus. Retrofenstral/cochlear otosclerosis: Lucency surrounding the bony labyrinth has a molted appearance on CT. CPA Epidermoid Cyst Congenital benign lesion arising from displaced ectodermal rests during neural tube closure. Slow growing cyst which accumulate keratin and cholesterol from epithelial desquamation. Imaging: “Light bulb bright” on DWI, T2 isointense to CSF. Symptoms: SNHL, vertigo, headache, trigeminal neuralgia (with CNV involvement). B B A A A) CSF isointense lesion on T2WI within the right CPA cistern, contacting CNVII/VIII. The cyst displaced the CNV nerve at its cisternal segment (not shown). B) The mass restricts diffusion on DWI. Labyrinthine Ossificans Ossification of the membranous labyrinth as a response to a inflammatory or traumatic insult. Most commonly occurs as bilateral SNHL in infants after acute meningitis. Less common causes include prior surgery, trauma, middle ear infection, autoimmune disease. Temporal bone CT: Findings range form increased density within the membranous labyrinth to complete obliteration. May impede successful cochlear implantation. Labyrinthine ossificans secondary to prior surgery. CT images show a focus of increased density within the fluid filled spaces of the cochlea. Arteriovenous Fistula A congenital malformations which typically presents later in life. Although most are asymptomatic, some may become symptomatic due to turbulent vascular flow or venous infarction with compromised venous outflow. Imaging: MR/CTA or angiography. Patient presented with pulsatile tinnitus. Angiography reveals an AV fistula draining to the left transverse and sigmoid sinuses, with the major inflow artery arising from left ICA. The severely stenotic left sigmoid sinus drains via the contralateral right transverse and sigmoid sinuses. A) Prominent vascular malformation extending into the left temporal lobe on post contrast T1W images. B) Signal loss on susceptibility weighted images highlights the pronounced vascularity. A A B B 1. Internal Auditory Canal 2. Cochlea 3. Vestibule 4. Vestibular Aqueduct 5. Incus 6. Malleus 7. Facial Nerve Canal 8. Lateral Semicircular Canal 9. CNVII/CNVIII Nerve Complex 10. Cerebellopontine Angle 11. Medial Geniculate Ganglia 12. Heschl’s Gyrus 2 7 1 2 3 4 5 6 7 12 11 10 9 8 2