True terminal pentafurcation of the external carotid artery and terminal trifurcation of the contralateral one, occipitoauricular trunk, retropharyngeal internal carotid artery

Abstract

The external carotid artery (ECA) commonly ascends in the retromandibular fossa and bifurcates posteromedial to the neck of the mandible into the maxillary (MA) and superficial temporal (STA) arteries. In its course in the neck, the ECA gives off the superior thyroid, lingual (LA), facial (FA), ascending pharyngeal (APA), occipital (OA) and posterior auricular (PAA) arteries. When the computed tomography angiograms of a 65-year-old male were evaluated, extremely rare anatomical variations of both ECAs were found. The right ECA trifurcated terminally at the neck of the mandible into the MA, STA and middle meningeal artery (MMA). A right occipitoauricular trunk was found coursing posterior to the ECA to further divide in the parotid region into the OA and PAA. The left ECA had a terminal pentafurcation, with the FA/APA/OA/MA/STA pattern, and the PAA branched from the STA. This pentafurcation occurred deep to the angle of the mandible and the medial pterygoid muscle, in front of the internal jugular vein. The MA ascended behind the medial pterygoid muscle, deep to the posterior border of the ramus of the mandible and reached the lateral pterygoid muscle to continue normally. The right internal carotid artery (ICA) had a lower medial curvature intercalated between the third cervical vertebra and the pharynx. To the authors’ knowledge, a terminally pentafurcated ECA has not been previously recorded, and a terminal trifurcation with an added MMA has only been observed once. Such drastically modified arterial patterns expose the branches emerging from the pentafurcation and pose a risk during surgical approaches within the parotid region. Additionally, a retropharyngeal curvature of the ICA could be subject to compression during deglutition.