Venous Component Of The Jugular Foramen

The venous component of the jugular foramen consists of a large posterolateral venous channel (sigmoid part), which receives flow from the sigmoid sinus, and a smaller anterome-dial venous channel (petrosal part), which receives drainage from the IPS. The sigmoid sinus courses anteroinferiorly toward the jugular foramen, continuing as the jugular bulb, and then as the internal jugular vein. The dome of the jugular bulb is located approximately 2 mm inferior to the internal auditory canal. The dome of the jugular bulb may extend superiorly to the posterior wall of the internal auditory canal, in which case it is referred to as a "high jugular bulb"10,11 (Fig. 82-2).

The IPS courses on the intracranial surface of the petrocli-val fissure and enters the anteromedial (petrosal) part of the

Figure 82-1 Endocranial and exocranial views of the jugular foramen. (A) Endocranial view shows cranial nerve (CN) IX is separated from CNs X and XI by a dural septum. The inferior petrosal sinus courses inferior to CN IX as the nerve enters the jugular foramen and courses between CN IX and X to drain into the anterior aspect of the jugular bulb. (B) Exocranial view of CNs and regional vascular relationships. CN XI courses posterolateral to the internal jugular vein. CN IX is lateral to CNs X and XI and is anchored to the internal carotid artery by a dense fibrous band. ICA, internal carotid artery; IPS, inferior petrosal sinus; SPS, superior petrosal sinus; SS, sigmoid sinus; StS, straight sinus; SSS, superior sagittal sinus; OS, occipital sinus; ELS, endolymphatic sac; CEV, condylar emissary vein; IJV, internal jugular vein; A, dural septum; B, superior ganglion of CN IX; C, inferior ganglion of CN IX; D, superior ganglion of CN X. (Reprinted with permission from the Mayfield Clinic.)

Figure 82-1 Endocranial and exocranial views of the jugular foramen. (A) Endocranial view shows cranial nerve (CN) IX is separated from CNs X and XI by a dural septum. The inferior petrosal sinus courses inferior to CN IX as the nerve enters the jugular foramen and courses between CN IX and X to drain into the anterior aspect of the jugular bulb. (B) Exocranial view of CNs and regional vascular relationships. CN XI courses posterolateral to the internal jugular vein. CN IX is lateral to CNs X and XI and is anchored to the internal carotid artery by a dense fibrous band. ICA, internal carotid artery; IPS, inferior petrosal sinus; SPS, superior petrosal sinus; SS, sigmoid sinus; StS, straight sinus; SSS, superior sagittal sinus; OS, occipital sinus; ELS, endolymphatic sac; CEV, condylar emissary vein; IJV, internal jugular vein; A, dural septum; B, superior ganglion of CN IX; C, inferior ganglion of CN IX; D, superior ganglion of CN X. (Reprinted with permission from the Mayfield Clinic.)

Figure 82-2 Inferior petrosal sinus/anterior condylar vein complex. BP, basilar plexus; ICA, internal carotid artery; IPS, inferior petrosal sinus; JF, jugular foramen; SPS, superior petrosal sinus; SS, sigmoid sinus; ACV, anterior condylar vein; PCV, posterior condylar vein; MS, marginal sinus; IJV, internal jugular vein. (Reprinted with permission from the Mayfield Clinic.)

Figure 82-2 Inferior petrosal sinus/anterior condylar vein complex. BP, basilar plexus; ICA, internal carotid artery; IPS, inferior petrosal sinus; JF, jugular foramen; SPS, superior petrosal sinus; SS, sigmoid sinus; ACV, anterior condylar vein; PCV, posterior condylar vein; MS, marginal sinus; IJV, internal jugular vein. (Reprinted with permission from the Mayfield Clinic.)

jugular foramen between CN IX and CN X. The IPS receives tributaries from the inferior petroclival vein (venous plexus in the carotid canal), venous plexus of the hypoglossal canal (anterior condylar vein), posterior condylar vein (emissary vein), and from the vertebral venous plexus. This confluence fills the anteromedial compartment of the jugular foramen, consisting of one or sometimes two main channels that receive drainage from smaller channels.

Shiu et al.12 described a classification system for the inferior petrosal sinus/anterior condylar vein complex that was further refined by Miller et al.13 In type I (45% of cases), the IPS drains directly into the jugular bulb and connects with the suboccipital and vertebral venous plexus via a small anterior condylar vein. In type II (24%), the IPS joins an anterior condylar vein of similar size before draining into the jugular bulb. Type III (24%) occurs when the IPS is formed of small venous channels connected to the jugular bulb. In type IV (7%), the IPS is not connected to the jugular bulb, but anastomoses directly with the vertebral and suboccipital venous plexi and may send a small tributary to the internal jugular vein. In summary, the IPS/anterior condylar vein complex forms an anastomosis with the jugular bulb in more than 90% of patients.

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