Conductive Hearing Loss From a Jugular Bulb Anomaly
The differential diagnosis included juvenile otosclerosis, congenital stapes footplate fixation, lateral ossicular chain fixation, ossicular discontinuity/malformation, middle ear paraganglioma, enlarged vestibular aqueduct, and other third window conditions. A high-resolution computed tomography (CT) of the temporal bone with and without contrast was obtained. Contrasted images were obtained to rule out a vascular neoplasm given the otoscopy findings. Axial and coronal images demonstrated a right high-riding and dehiscent jugular bulb (Fig. 1). The jugular bulb protrudes into the posterior mesotympanum and obstructs the round window niche, thus meeting criteria for high-riding. Additionally, this protrusion is not covered by bone and is, therefore, classified as dehiscent. It approached, but did not clearly contact, the incudostapedial joint. There were no other abnormal radiographic findings. Management options of observation, a hearing aid, or surgical intervention were discussed. The family agreed to the primary recommendation of observation.
The jugular bulb is located below the hypotympanum of the middle ear (1). The size, location, and configuration of the jugular bulb is variable. Jugular bulb abnormalities (JBA) represent congenital venous malformations with variants that include a high-riding jugular bulb (HRJB), dehiscence, protrusion, or diverticulum. These variants all have specific definitions and the case illustrated in this report meets criteria for both high-riding and dehiscent.
The incidence of HRJB is 6 to 34%. JBA may be present in all ages without a sex predilection and they may evolve with skeletal growth into the fourth decade of life (2). Dehiscence is more common on the right side. Patients may be asymptomatic or have symptoms including CHL, pulsatile tinnitus, or vertigo (3).
Hearing loss observed in patients with JBA has been attributed to one of three mechanisms: interference with the tympanic membrane, interference with the ossicular chain, or obstruction of the round window niche (4). The round window membrane releases mechanical energy transmitted from the stapes footplate. Obstruction of the round window inhibits the transfer of energy, which reduces compliance of the sound-conduction mechanism and results in CHL (4). Round window obstruction is the mechanism of hearing loss in this illustrated case.
The primary management strategy for JBA is observation. Surgical manipulation of the JBA or lateralization of the tympanic membrane have been reported but are rarely indicated (5). Procedures that could disrupt venous flow in the JBA risk increasing intracranial pressure. In summary, this case illustrates a rare finding of a dehiscent high riding jugular bulb with a diverticulum that obstructs the round window. The lesion was identified with a CT temporal bone, which is the imaging modality of choice to investigate a CHL of unknown etiology.