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Internal Jugular Bulb

bulbus venae jugularis

The jugular bulb is the dilation of the internal jugular vein at the jugular foramen, where the sigmoid sinus transitions to the IJV. It lies in the jugular fossa — a depression in the inferior petrous bone — immediately posteroinferior to the middle ear. The jugular bulb varies considerably in size (3-15 mm in height) and position; a high-riding dehiscent jugular bulb protrudes into the middle ear space and is visible as a bluish pulsatile mass through the tympanic membrane.

Region: Head & Skull

Clinical Relevance

Clinical Notes

Jugular bulb anatomy is critical in posterior fossa and temporal bone surgery. A high-riding jugular bulb limits the inferior exposure of the posterior fossa and may complicate cochlear implant insertion and posterior petrous approaches. A dehiscent jugular bulb (absent bony covering) in the middle ear creates a risk of catastrophic haemorrhage during middle ear surgery if the bulb is inadvertently entered. CT imaging of the petrous bone identifies jugular bulb position and dehiscence pre-operatively. Jugular bulb dominance (usually right-sided) is relevant in sigmoid sinus occlusion treatment planning.

Pathology

Common Injuries & Conditions

Dehiscent Jugular Bulb Mimicking Middle Ear Tumour

A high-riding dehiscent jugular bulb protruding through the floor of the middle ear presents as a bluish pulsatile retrotympanic mass mimicking a glomus tympanicum tumour; CT temporal bone (not biopsy) distinguishes the vascular bulge from a true tumour, and attempted biopsy of a dehiscent jugular bulb would produce life-threatening haemorrhage.