32
3.5
3
External Carotid Artery
Occipital Artery
The occipital artery takes its origin from the posterior wall of the ECA, frequently as a common trunk with the APhA (Figs. 3.5 and 3.8). The occipital artery can sometimes arise from the vertebral artery or ICA (Fig. 3.8). It runs posteriorly and slightly superiorly with an undulating course, in which three segments may be identified: the first ascending, the second horizontal, and the third ascending again. It gives off several musculocutaneous branches for the neck and posterior part of the head and meningeal branches, among which the following are the most important: 1. The stylomastoid artery arises from the first segment and runs up to the stylomastoid foramen, accompanying the facial nerve supplying it. It anastomoses superiorly with the superior tympanic artery, arising from the petrosquamous artery branch of the middle meningeal artery. The stylomastoid artery also gives off branches for the tympanic cavity and adjacent area (posterior tympanic artery), where they anastomose with the other tympanic branches arising from the APhA and IMA. The stylomastoid artery can arise from the posterior auricular artery or directly from the trunk of the ECA. It is a fine branch, not always evident on the lateral ECA angiogram. It can be dilated and well recognizable when involved in the supply of pathological processes (Figs. 3.22, 3.24c, and 13.1). 2. Of the muscular branches, two arise in the ascending segment. A third branch (the splenial artery) arises from the horizontal segment, has a descending course, and supplies the splenius muscle. The muscular branches can anastomose with corresponding branches of the vertebral artery at the C1–C2 level and with branches of the ascending cervical artery (Figs. 3.7, 3.8, and 15.20). 3. The mastoid branch (Fig. 3.7) arises from the second segment, approximately near the origin of the splenial artery. It has an ascending course, enters the cranial cavity through the foramen of the emissary vein, and supplies the meninges of the cerebellopontine angle and cerebellar fossa. These branches are in hemodynamic balance with those arising from the
Fig. 3.7 Angiogram of the external carotid artery (lateral view). Occipital artery (O), with its muscular branches from the ascending segment and horizontal segment; splenial artery (S). Mastoid branch (M), posterior auricular artery (PA), superficial temporal artery (STA), internal maxillary artery (IMA)
neuromeningeal trunk of the APhA, with the petrosquamosal branch of the middle meningeal artery (MMA), and with the meningeal branches of the vertebral artery (Lasjaunias et al. 1978b). One of these branches can dominate and completely supply these territories. The occipital artery is involved in several pathological processes (Figs. 3.21, 3.22, 13.1, 13.8, 13.10, 13.11, 13.13, and 13.18).
3.6
Posterior Auricular Artery
This is a small branch arising near the terminal ECA (Fig. 3.7), sometimes as a common trunk with the occipital artery. It supplies the pinna of the ear, which is frequently evident as a blush in the capillary phase of the ECA angiogram.
3.7
Internal Maxillary Artery
The IMA is the larger of the terminal branches of the ECA. It originates behind the neck of the mandible, within the parotid gland. It runs obliquely forward and medially in the masticator