Figure 1
Teaching Case
SectionHead & neck imaging
Case TypeAnatomy and Functional Imaging
AuthorsO'Connor SA, Hanson JM, Quinn AD
Connected authors
56 years, male
A 56-year-old gentlemen presented with numbness and tingling in the left arm and leg, on a background of hypercholesterolemia and previous coronary artery bypass graft (CABG). Carotid doppler was performed with a very limited view of both the left vertebral artery and internal carotid. A CT carotid angiogram was therefore performed.
Anomalous origin of occipital artery from pharyngo-occipital trunk
Anomalous anatomy
Surgical by-pass
Normal variant anatomy, in that the left occipital artery is arising from the left internal carotid artery. Usually there are no branches arising from the extracranial internal carotid artery
Anomalies in the extracranial carotid circulation are frequently seen and are usually asymptomatic. Most of these variants occur in the distribution of the external carotid artery (ECA) and are rarely seen to involve the internal carotid artery (ICA).
The ICA is derived from the combination of the third aortic arch, the cranial extension of the dorsal aorta and the ventral aortic sac (1). While various segments coalesce to form the intracranial portion, the third arotic arch is most notably involved with the extracranial extent of the vessel’s development (1, 2).
The occipital artery (OA) usually arises from the posterior aspect of the ECA at the level of the external maxillary artery, near the lower border of the posterior belly of the digastic muscle, and extends forward to supply muscles of the orbital region including the recti muscles, superior and inferior oblique and the occipitalis muscles, before ascending posteriorly and ultimately terminating in the posterior part of the scalp (3, 5). However, a limited number of cases have identified incidences of the OA arising from a pharyngo-occipital trunk or directly from the ICA (3-9). While this is generally an incidental finding, recognition of this variant is important as anastomosis of the OA with the vertebral artery is not uncommon and has significant implications, particularly in the setting of carotid endarterectomy, where it can maintain perfusion to the brain but can also result in back bleeding during the procedure if not accounted for (6, 9). The variant also has implications on plaque location in thromboembolic disease and intra-arterial catheterization (9).
Review of the literature suggests that this anomaly is more likely to occur to the right OA than the left and in a unilateral manner; only being reported once occurring bilaterally (5). The embryological cause is poorly understood, however Lasjaunas et al. hypothesized that the OA arising from the ICA is a persistent proatlantal intersegmental artery. This continues to be the leading hypothesis to date.
The ICA is derived from the combination of the third aortic arch, the cranial extension of the dorsal aorta and the ventral aortic sac (1). While various segments coalesce to form the intracranial portion, the third arotic arch is most notably involved with the extracranial extent of the vessel’s development (1, 2).
The occipital artery (OA) usually arises from the posterior aspect of the ECA at the level of the external maxillary artery, near the lower border of the posterior belly of the digastic muscle, and extends forward to supply muscles of the orbital region including the recti muscles, superior and inferior oblique and the occipitalis muscles, before ascending posteriorly and ultimately terminating in the posterior part of the scalp (3, 5). However, a limited number of cases have identified incidences of the OA arising from a pharyngo-occipital trunk or directly from the ICA (3-9). While this is generally an incidental finding, recognition of this variant is important as anastomosis of the OA with the vertebral artery is not uncommon and has significant implications, particularly in the setting of carotid endarterectomy, where it can maintain perfusion to the brain but can also result in back bleeding during the procedure if not accounted for (6, 9). The variant also has implications on plaque location in thromboembolic disease and intra-arterial catheterization (9).
Review of the literature suggests that this anomaly is more likely to occur to the right OA than the left and in a unilateral manner; only being reported once occurring bilaterally (5). The embryological cause is poorly understood, however Lasjaunas et al. hypothesized that the OA arising from the ICA is a persistent proatlantal intersegmental artery. This continues to be the leading hypothesis to date.
References
[1] Cakirer S,Karaarslan E,Kayabali M,Rozanes I (2002) Separate Origins of The Left Internal and External Carotid Arteries from the Aortic Arch:MR Angiographic Findings. AJNR 23:1600-2 (PMID: 12372755)
[2] Gailloud P, Clatterbuck R.E, Fasel J.H.D, Tamargo R.J, Murphy K.J (2004) Segmental Agenesis of the Internal Carotid Artery distal to the Posterior Communicating Artery leading to the definition of a new embryologic segment. AJNR 25: 1189-1193 (PMID: 15313707)
[3] Aggarwal NR, Krishnamoorthy T, Devasia B, Menon G, Chandrasekhar K (2006) Variant origin of superior thyroid artery, occipital artery and ascending pharyngeal artery from a common trunk from the cervical segment of internal carotis artery. Surg Radiol Anat 28(6):650-3 (PMID: 17024310)
[4] Benson MT, Hamer JD (1988) Anomalous origin of the occipital artery from the cervical internal carotid artery. J Vasc Surg 8(5):643-5 (PMID: 3184318)
[5] Matsuda I, Handa J, Handa H, Mizuno H (1977) Bilateral anomalous occipital artery of internal carotid artery origin: case report. Nihon Geka Hokan 46(1):57-61 (PMID: 561577)
[6] Newton TH, Young DA (1973) Anomalous origin of the occipital artery from the internal carotid artery. Radiology 90(3):550-2 (PMID: 5642292)
[7] Teal JS, Rumbaugh CL, Segall HD, Bergeron RT (1973) Anomalous branches of the internal carotid artery. Radiology 106(3):567-73 (PMID: 4684800)
[8] Iwai T, Izumi T, Inoue T, Maegawa J, Fuwa N, Mitsudo K, Tohnai I (2012) Occipital artery arising form the anterior aspect of the internal carotid artery identified by three-dimensional computed tomography angiography. Iran J Radiol 9(2):103-105 (PMID: 23329973)
[9] Graham R, Sugrue P, Rahme R, et al (2013) Pharyngo-occipital artery variant arising from the internal carotid artery impacting surgical technique during carotid endarterectomy. J NeuroIntervent Surg 5(3) (PMID: 22442404)
Case information
| URL: | https://eurorad.org/case/11079 |
| DOI: | 10.1594/EURORAD/CASE.11079 |
| ISSN: | 1563-4086 |
Figure 1
Dr J Hanson
