Dehiscent jugular bulb : CT

 Case Report : 43 year male patient presents with complaint of chronic giddiness for HRCT mastoid which showed dominant high riding dehiscent jugular bulb on left side protruding into left middle ear cavity. Jugular bulb could not be made out on right side – likely hypoplastic.

Salient points by Dr MGK Murthy, Dr Rajshekhar, Dr GA Prasad. 

-        The superior border of the jugular bulb normally lies below the hypotympanum of the middle-ear cavity. However, in rare cases the jugular bulb may extend upwards, elevating the floor of the hypotympanum and presenting in the middle-ear space with a thin or absent bony septum. This anomaly is known as a high-riding jugular bulb. A jugular bulb is also considered high-riding if it extends superior to the level of tympanic annulus, or encroaches within 2mm of the internal auditory canal (IAC).

-        A high-riding jugular bulb has an intact sigmoid plate - a thin plate of bone separating the jugular bulb from the middle-ear cavity.. If the sigmoid plate is deficient, the bulb is free to protrude into the middle-ear cavity, and is then known as a dehiscent jugular bulb.

-        Symptoms - tinnitus and conductive hearing loss, which may be ascribed to turbulent blood flow through the aberrant anatomy resulting in unwanted sound transmission through the middle-ear apparatus.

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Otoscopically, this is seen as a blue mass behind an intact tympanic membrane, which may become distended on valsalva or ipsilateral jugular compression.

-        Great care should be taken by the surgeon if a high- riding jugular bulb is preoperatively identified which predisposes to surgical complications during myringotomy or middle-ear surgery. If high-riding jugular bulb has been found to be impinging on the ossicles or round window niche, it is prudent to abort the operation and to look for conservative management to the extent possible.

-         High jugular bulb is not a contraindication for middle-ear surgery. Awareness of this pitfall may lessen the operation risk.  HRCT is the imaging modality of choice for evaluating the jugular bulb.