Clinical History
A male patient, 34 years old, complaining of right-sided tinnitus.
Imaging Findings
The right internal jugular vein (IJV) at the skull base shows a high riding bulb reaching up to a level where the internal auditory canal (IAC) can be seen. The IJV is seen protruding into the middle ear cavity with the bony boundary (sigmoid plate) thinned out.
Discussion
Background: The jugular bulb is the highest most dilated portion of the jugular vein at its junction with the sigmoid sinus. It is said to be high riding when it extends superior to the floor of the IAC. In the presence of dehiscent sigmoid plate, the jugular vein extends supero laterally from the jugular foramen into the middle ear cavity. On otoscopy, it can be seen as a bluish retro tympanic mass [1].
Clinical perspective: High riding jugular bulb with dehiscent sigmoid plate is an anatomic variant that may be associated with tinnitus. The differential diagnosis of tinnitus encompasses a variety of aetiologies, however, pulsatile tinnitus points to an underlying vascular aetiology. Vascular aetiologies include (a) vascular neoplasms (b) vascular malformations (c) vascular anatomic variants (d) others: arterial aneurysm, atherosclerotic disease etc. [1].
The true association of jugular bulb variant and tinnitus is still a matter of controversy in literature. Some believe that even if a jugular bulb variant is detected on imaging, one should search for another treatable cause [2].
Imaging perspective: Computed Tomography (CT) is the modality of choice in revealing jugular bulb variants, especially a dehiscent sigmoid plate. Implementing thin sections, bone algorithm, high resolution images suffice assessment of the skull base anatomy [1, 2].
Outcome: The importance of the detection of such variants lies in preventing catastrophic events in middle ear surgeries. It is therefore critically important to report such a finding to the surgeon [3].
Differential Diagnosis List
High riding jugular bulb with dehiscent sigmoid plate
Other vascular anatomic variants associated with tinnitus:
Aberrant carotid artery
Persistent stapedial artery
Jugular diverticulum
Final Diagnosis
High riding jugular bulb with dehiscent sigmoid plate
