Ascending pharyngeal-vertebral anastomosis demonstrated by computed tomography angiography of the ascending pharyngeal artery: a case report

Case report

A 57-year-old man was admitted to our hospital with intermittent epistaxis. One year earlier, he had received radiotherapy with systematic chemotherapy for a right maxillary tumor, followed by a total maxillectomy with microsurgical anastomosis between the right superficial temporal artery and a vascularized flap used as a reconstructed deep inferior epigastric artery (DIEA).

Magnetic resonance imaging showed a recurrent maxillary tumor in the right nasal cavity, and transarterial chemoembolization was planned for control of the epistaxis. An interventional procedure was performed via a transfemoral route. The reconstructed DIEA, a right maxillary artery, and a right ophthalmic artery arising from the internal carotid artery (ICA) were identified as feeding arteries. To search for another feeding artery, we also performed selective injection of the right APA. Digital subtraction angiography (DSA) images did not reveal tumor staining, but showed incidental visualization of the right VA (Fig. 1). On CTA of the APA, the vessel entered the hypoglossal canal and connected with the right VA (Fig. 2). These findings were compatible with APA-VA anastomosis via the hypoglossal branch of the neuromeningeal trunk.

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Transarterial chemotherapy was performed through the reconstructed DIEA, internal maxillary artery, and ICA. Embolization of the reconstructed DIEA and internal maxillary artery was also performed using Gelfoam^® particles.

The epistaxis diminished and the patient was discharged. We retrospectively reviewed a CT angiogram obtained by preoperative intravenous contrast-enhanced CT, which showed hypoplasia of the right VA.

Discussion

The APA usually arises from the proximal portion of the ECA and divides into two major trunks: anteriorly, the pharyngeal trunk, which mainly supplies pharyngeal tissue; and posteriorly, the neuromeningeal trunk, which supplies the dura and lower cranial nerves of the skull base (6, 8). The two main divisions of the neuromeningeal trunk are the jugular and hypoglossal branches. The former enters the cranial cavity through the jugular foramen, supplying the ninth, 10th, and 11th nerves (7). The latter extends to the meninges of the posterior fossa and the vasa nervorum of the 12th cranial nerve. The hypoglossal branch has a medially descending branch that anastomoses with the VA at the third cervical space, forming an extradural arcade dorsal to the body of the dens of C-2; this constitutes the arterial arcade of the odontoid process (7-10). Since the routes of these two branches are closely aligned, the jugular branch can mimic the hypoglossal branch. Consequently, identification of the hypoglossal branch is sometimes difficult on DSA images (10).

Several reports have described cases of APA-VA anastomosis, but few have discussed angiography findings. Although most of these reported anastomoses were detected by angiography of the carotid artery, whereas we revealed this anastomosis by CTA of the APA. Extra-intracranial anastomotic channels are usually not visible on routine catheter angiographies, but are seen under the following circumstances: (a) with increased intra-arterial pressure (e.g. during embolization procedures or super-selective injections; (b) in the presence of high-flow shunts, as a consequence of the ‘sump effect’; and (c) as collateral routes in cases with occlusions of the major intracranial arteries (11). In our case, the ascending pharyngeal-vertebral anastomosis was not visible on a right external carotid arteriogram, but was seen after selective injection into the APA. This indicates that increased intra-arterial pressure contributed to visualization of the anastomosis. In addition, hypoplasia of the right VA might have contributed to formation of the anastomosis as a collateral route. In fact, it is known that hypoplasia of the VA causes carotid artery-VA anastomosis, occipital artery-VA, persistent trigeminal artery-VA, and persistent primitive artery-VA (12-14). Whereas the lower cranial nerves are supplied from the vertebral arteries, the supply to their foraminal parts is mainly through the neuromeningeal trunk of the APA (7, 8, 11). Damage of the VA area in interventional procedures for the APA has not been reported, but there is a risk of such damage.

In conclusion, we have described a case of APA-VA anastomosis accompanied with hypoplasia of the VA. CTA of the APA showed that the anastomosis entered the hypoglossal canal and connected with the right VA. Interventional radiologists should be aware of this potential anastomotic route of the APA to the VA, especially under a condition of hypoplasia of the VA detected on preoperative images.