Jugular Foramen: Anatomy, Contents, and Clinical Notes

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-20

The jugular foramen is an irregular opening in the caudal part of the skull base, formed between the occipital bone and the temporal bone, that transmits cranial nerves IX (glossopharyngeal), X (vagus), and XI (accessory), together with the inferior petrosal sinus and the sigmoid sinus as it becomes the internal jugular vein. It is the venous and lower-cranial-nerve gateway between the intracranial cavity and the neck.

This opening matters because it is a shared corridor. Three cranial nerves and the brain's main jugular drainage pass through a space only a few millimeters across, so any mass, infection, fracture, or vascular anomaly in this region can produce a recognizable cluster of deficits. In dogs, dysfunction of cranial nerves IX, X, and XI from a lesion at the jugular foramen is called jugular foramen syndrome, and it is most often caused by neoplasia [1].

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Where the Jugular Foramen Sits

The jugular foramen lies at the junction of the occipital and temporal bones, at the caudal end of the petro-occipital fissure [2]. It sits posterior to the carotid canal, which carries the internal carotid artery and its sympathetic plexus. The two openings are close neighbors but carry completely different contents, and confusing them is a classic student error.

The foramen is not a simple round hole. Its intracranial opening (the end you see from inside the skull) and its extracranial opening (the end you see from the neck side) differ in shape and in the number of bony spurs that project into them. Triantafyllou and colleagues found that intrajugular processes were present at the intracranial orifice in 41% of specimens but at the extracranial orifice in only 19.5%, and that the compartments of the foramen became progressively narrower as the number of these processes increased [3].

The term "jugular canal" is sometimes used for the tubular, extracranial continuation of the foramen as it opens into the jugular fossa and the neck. "Foramen jugular" is simply the Latin form of the same structure. All three terms describe one region, and the practical difference is whether you are describing the intracranial rim, the bony tunnel, or the external opening.

Bony Landmarks to Know

• Jugular fossa. The depression on the inferior surface of the petrous temporal bone that houses the jugular bulb, the dilated origin of the internal jugular vein.
• Carotid canal. Lies anterior and medial to the jugular foramen and transmits the internal carotid artery.
• Stylomastoid foramen. Lies lateral and slightly anterior, transmitting the facial nerve (CN VII). The distance between the jugular foramen and the stylomastoid foramen is a standard morphometric parameter in the literature [2][4].
• Hypoglossal canal. Lies medial to the jugular foramen and transmits cranial nerve XII. Lesions that involve both the jugular foramen and the hypoglossal canal produce combined palsies of CN IX, X, XI, and XII, known as Collet-Sicard syndrome [5][6].
• Internal acoustic meatus. Lies dorsolateral to the jugular foramen on the petrous face. The mean distance between the two is approximately 6 mm in humans [4].

The Two Compartments: Pars Nervosa and Pars Vascularis

Textbooks divide the jugular foramen into an anteromedial pars nervosa and a posterolateral pars vascularis. This bipartite model is the one most students learn first, and it is the model you should be able to draw from memory.

Pars nervosa (anteromedial compartment). Contains cranial nerve IX (glossopharyngeal) and the inferior petrosal sinus. The inferior petrosal sinus drains the cavernous sinus and runs along the petro-occipital fissure before emptying into the jugular bulb.

Pars vascularis (posterolateral compartment). Contains cranial nerves X (vagus) and XI (accessory), the sigmoid sinus, and the jugular bulb. The sigmoid sinus is the continuation of the transverse sinus. As it passes through the foramen it dilates into the jugular bulb, which then continues caudally as the internal jugular vein.

The partition between the two compartments is usually a fibrous or fibro-osseous bridge, not a complete bony wall. Bond and Zhang reviewed the compartmentalization literature and noted that no single model has achieved consensus, and that the bipartite model has been criticized as oversimplified and lacking surgical validity [7]. Tripartite models that account for the dura and the extradural neural axis compartment may be more anatomically faithful [7].

Saleh and colleagues made the practical point that the classic compartments are not always present. In their dissection series, cranial nerves IX through XI followed different patterns as they crossed the foramen, and were separated from the jugular bulb by bone, thick fibrous tissue, or only thin connective tissue depending on the individual [8]. That variability is why a surgeon cannot assume a clean plane between nerve and vein.

Bony and Dural Septations

Bony septations within the jugular foramen are common enough that every clinician working in this region should expect them. Reported frequencies vary with the population and the method:

• Fang and colleagues found bony bridges in 8.5% of sides, bilateral in 3% of skulls, with incomplete (type I) bridges in 47% of affected sides and complete (type II) bridges in 53%. Multiple septa occurred in 2.5% of sides [9].
• Hathaidechadusadee and Chentanez identified bony septation in 42.8% of foramina, most commonly type I (37.3%), followed by type II (5.0%) and type III (0.5%). Type I septa most often arose from the temporal bone. Dural septation was present in every cadaver they examined, with type I predominating at 89.7% [4].
• Triantafyllou and colleagues found accessory foramina, interpreted as ossified dural septations, in 2.92% of skulls as complete and 0.42% as incomplete. When present, these significantly reduced the height and width of the jugular foramen [10].

The clinical takeaway is straightforward. A bony or ossified septum narrows the working space around the lower cranial nerves and can make intraoperative manipulation more hazardous [10].

Right-Left Asymmetry

The right and left jugular foramina are not mirror images. Meta-analysis of 5,204 foramina found significant asymmetry, with the right side generally larger across all measured parameters [2]. Hathaidechadusadee and Chentanez confirmed that the foramen was consistently larger on the right in both length and width, and that the sigmoid sinus was significantly larger on the right and in males [4]. Triantafyllou and colleagues also reported right-sided predominance for intracranial dimensions [3].

This asymmetry is normal anatomy, not pathology. It becomes relevant when you are interpreting imaging, because a larger jugular bulb on one side is expected and should not be mistaken for a vascular lesion.

Contents Table

Comparative Anatomy: Dogs, Cats, and Horses

Carnivores and horses share the same fundamental arrangement. The jugular foramen sits between the occipital and temporal bones, posterior to the carotid canal, and transmits cranial nerves IX, X, and XI along with the venous drainage that becomes the internal jugular vein.

The foramen is relatively larger in dogs than in cats. This size difference reflects the larger jugular bulb and the more prominent venous drainage in the dog, and it is one reason the jugular vein is such a convenient venipuncture site in that species. In horses, the jugular groove is a defining clinical landmark, and the internal jugular vein is the standard route for large-volume fluid therapy and for many drug administrations. The foramen itself is proportionally smaller relative to the massive equine skull, but the contents are the same.

The comparative point that matters most for clinical work is this. In dogs, lesions at the jugular foramen produce a syndrome that has now been characterized in the veterinary literature. Madden and colleagues reviewed 14 dogs with jugular foramen syndrome diagnosed by advanced imaging between 2016 and 2024. Affected dogs were older, with a median age of 9.9 years and a range of 7.9 to 14.5 years, and they presented with chronic progressive signs, with a median duration of 135 days and a range of 5 to 720 days [1]. The most common presenting complaints were coughing in 7 of 14 dogs, retching in 6 of 14, head tilt in 5 of 14, and laryngeal stridor in 4 of 14. Neurologic abnormalities were found in 11 of 14 dogs, and cranial nerve deficits in 10 of those 11, with unilateral laryngeal paralysis in 5 of 10 and tongue atrophy in 4 of 10 being most common. Intracranial lesions were identified in 10 of 14 dogs, with meningioma the most frequent diagnosis. In the 4 dogs with extracranial lesions, thyroid carcinoma was common. Median survival time was 218 days, with a range of 16 to 477 days [1].

That pattern is worth memorizing because it is the opposite of what many students expect. The classic teaching is that jugular foramen lesions cause dysphagia and voice change. In dogs, the most common owner-reported complaints were coughing and retching, not dysphagia.

How the Foramen Is Examined and Imaged

The jugular foramen is not directly visible on physical examination. You assess it indirectly through the functions of the structures that pass through it.

Cranial nerve IX (glossopharyngeal). Test the gag reflex and observe swallowing. Loss of sensation in the caudal pharynx and absent gag are the expected findings.

Cranial nerve X (vagus). Assess laryngeal function. Unilateral laryngeal paralysis is a common finding in dogs with jugular foramen syndrome [1]. In the clinic, laryngeal paralysis is confirmed by direct laryngoscopy under light anesthesia, watching for failure of the arytenoid cartilage to abduct on inspiration.

Cranial nerve XI (accessory). Assess the sternocephalicus, brachiocephalicus, and trapezius muscles. In dogs, atrophy or weakness of these muscles produces a visible asymmetry of the neck and shoulder. In the human literature, the equivalent finding is drooping of the shoulder and weakness of the sternocleidomastoid [6].

Cranial nerve XII (hypoglossal). Although CN XII passes through the hypoglossal canal rather than the jugular foramen, tongue atrophy is frequently reported alongside jugular foramen lesions because the two openings are close and lesions often span both. Tongue atrophy was found in 4 of 10 dogs with cranial nerve deficits in the Madden series [1].

For imaging, computed tomography (CT) and magnetic resonance imaging (MRI) are the modalities of choice. CT is best for bony detail, including septations, the jugular dome, and the relationship to the carotid canal. MRI is best for soft tissue, including the nerves themselves and any mass. One meta-analytic finding is directly relevant to interpretation. MRI was associated with a significantly lower reported prevalence of high-riding jugular bulb compared with osteological assessment and CT-based techniques [11]. In other words, the modality you choose changes the number you get, so a "high jugular bulb" reported on one study type may not be reproduced on another.

Clinical Relevance, Limitations and Common Mistakes

Jugular foramen syndrome in dogs is a clinical diagnosis supported by advanced imaging. The Madden series is the largest veterinary dataset available and it establishes that neoplastic or suspected neoplastic causes are common, and that lesions often extend beyond the foramen by the time of diagnosis [1]. The same principle applies in humans. Collet-Sicard syndrome, which combines palsies of CN IX, X, XI, and XII, is most often caused by neoplastic lesions at the jugular foramen and hypoglossal canal, and benign tumors such as paragangliomas are less frequent causes [5][6].

Infectious causes are rare but documented. El-Saied and colleagues reported a case of jugular foramen syndrome in an adult patient caused by complicated acute otitis media, with thrombosis of the sigmoid sinus extending into the internal jugular vein and thrombophlebitis of the jugular vein [12]. The parallel in veterinary medicine is otitis media or interna with extension to the jugular bulb, which is a recognized complication of severe ear disease in dogs and cats. The clinical lesson is that jugular foramen syndrome does not always mean cancer.

Non-neoplastic mass-like lesions can also mimic tumors. Kim and colleagues described a sarcoid-like reaction with lymphoid infiltration arising around the jugular foramen and adhering to the cerebellum, medulla oblongata, and lower cranial nerves. The patient responded to corticosteroid therapy with clinical and radiographic improvement and no recurrence at 20 months [13]. The differential diagnosis for a jugular foramen mass is therefore broad and includes inflammatory and granulomatous disease, not only neoplasia.

Common mistakes students make.

1. Confusing the jugular foramen with the carotid canal. The carotid canal is anterior and transmits the internal carotid artery. The jugular foramen is posterior and transmits the lower cranial nerves and jugular vein.
2. Assuming the compartments are always present. Saleh and colleagues showed that the classic compartments are not always found, and that the separation between nerve and vein can be bone, thick fibrous tissue, or only thin connective tissue [8].
3. Forgetting the inferior petrosal sinus. Students remember the sigmoid sinus and the jugular bulb but forget that the inferior petrosal sinus drains into the jugular bulb through the pars nervosa.
4. Attributing all lower cranial nerve deficits to the jugular foramen. CN XII passes through the hypoglossal canal. When CN IX, X, XI, and XII are all affected, the lesion spans both openings, and the correct term is Collet-Sicard syndrome [5][6].
5. Treating right-left asymmetry as pathology. The right foramen is normally larger [2][3][4].
6. Expecting dysphagia to be the presenting complaint in dogs. Coughing and retching were more common in the veterinary case series [1].

Limitations. The veterinary literature on jugular foramen syndrome is limited to a single retrospective multicenter case series of 14 dogs [1]. Most of the detailed anatomical and morphometric data come from human cadaveric and imaging studies, which are useful for understanding the general arrangement but do not substitute for species-specific anatomy. Individual cases require assessment by a veterinarian, and imaging findings must be interpreted in the context of the whole patient.

Quick Review

1. The jugular foramen lies between the occipital and temporal bones, posterior to the carotid canal.
2. Pars nervosa contains CN IX and the inferior petrosal sinus.
3. Pars vascularis contains CN X, CN XI, the sigmoid sinus, and the jugular bulb, which continues as the internal jugular vein.
4. The foramen is normally larger on the right side.
5. Bony septations are common and can narrow the foramen, complicating surgery.
6. In dogs, jugular foramen syndrome presents most often with coughing, retching, head tilt, and laryngeal stridor, and neoplasia is the most common cause.
7. Collet-Sicard syndrome adds CN XII and involves the hypoglossal canal as well.

Frequently Asked Questions

What structures pass through the jugular foramen?

Cranial nerves IX, X, and XI, the inferior petrosal sinus, and the sigmoid sinus continuing as the internal jugular vein. The foramen is divided into an anteromedial pars nervosa and a posterolateral pars vascularis.

What is the difference between the jugular foramen and the jugular canal?

The jugular foramen is the opening in the skull base. The jugular canal is the tubular, extracranial continuation of that opening as it leads into the jugular fossa and the neck. They describe the same region at different points along its course.

What is jugular foramen syndrome in dogs?

It is dysfunction of cranial nerves IX, X, and XI caused by a lesion at the jugular foramen. In a series of 14 dogs, the most common presenting complaints were coughing, retching, head tilt, and laryngeal stridor, and neoplasia was the most frequent underlying cause [1].

Why is the right jugular foramen usually larger than the left?

Right-sided dominance is a normal anatomical finding reported across multiple morphometric studies. Meta-analysis of over 5,000 foramina found the right side larger across all measured parameters [2], and the sigmoid sinus is also significantly larger on the right [4].

What is Collet-Sicard syndrome?

It is combined palsy of cranial nerves IX, X, XI, and XII from a lesion involving both the jugular foramen and the hypoglossal canal. Neoplastic causes are most common, and benign tumors such as paragangliomas are less frequent [5][6].

Can an ear infection cause jugular foramen syndrome?

Yes, though it is rare. Complicated acute otitis media with sigmoid sinus thrombosis extending into the internal jugular vein has been reported as a cause in an adult patient [12]. In animals, severe otitis media or interna with extension to the jugular bulb is a recognized concern.

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Sources

1. Jugular Foramen Syndrome: Concurrent Neurological Deficits, Advanced Imaging Findings, Underlying Diagnoses, and Outcomes in 14 Dogs (2016-2024).
2. Variability and surgical anatomy of jugular foramen - a systematic review with a meta-analysis.
3. Morphological variability of the jugular foramen: a comprehensive anatomical-imaging study emphasizing its compartmentalization.
4. Comprehensive morphometric analysis of the jugular foramen and its septations in cadavers and dry skulls.
5. Collet-Sicard syndrome resulting from a Skull Base Paraganglioma: a case report.
6. Skull Base Squamous Cell Carcinoma Presenting as Collet-Sicard Syndrome: A Rare Cause of Multicranial Nerve Dysfunction.
7. Compartmental Subdivisions of the Jugular Foramen: A Review of the Current Models.
8. Lower skull base: anatomic study with surgical implications.
9. Variations and Classification of Bony Septations of the Jugular Foramen: An Anatomic and Histologic Study With Application to Imaging and Surgery of the Skull Base.
10. Accessory Foramina Presence Significantly Narrows the Jugular Foramen: Anatomical Study with Potential Neurosurgical Significance.
11. Clinical and surgical significance of the jugular foramen anatomy: systematic review with meta-analysis.
12. A Case Study and Concise Literature Review: Adult Patient's Initial Manifestation of Complicated Acute Otitis Media Presenting as Jugular Foramen Syndrome.
13. Tumor-mimicking sarcoid-like reaction with lymphoid infiltration showing intracranial extension from the left jugular foramen: illustrative case.