eRadiograph Volume 7: Imaging of Oral Cavity | Page 264

Introduction: These are paired tubular spaces surrounded by the carotid sheath which is formed by all 3 layers of the deep cervical fascia. Extent and Anatomy: The carotid space extends from the jugular foramen at the skull base to the aortic arch inferiorly. The carotid space is lateral to the RPS, posterolateral to PPS, medial to parotid space, anterolateral to prevertebral space, anteromedial to posterior cervical space. In the infrahyoid neck the visceral space is anteromedial to the carotid space. As the carotid space is a tubular space spanning the supra and infrahyoid neck, the carotid space can act as a conduit for pathological processes from the mediastinum to neck/skull base and vice versa. The carotid space can be divided into 4 parts – nasopharyngeal, oropharyngeal, cervical and mediastinal. Contents The contents of the carotid space in the suprahyoid neck are the internal carotid artery, IJV, cranial nerves IX, X, XI, XII, sympathetic nerves and lymph nodes. In the infrahyoid neck the contents are the common carotid artery, internal jugular vein, only cranial nerve X. Within the carotid space the carotid artery lies medial to the IJV, vagus nerve lies posterior to the vessels, the sympathetic chain is placed posterior. Pathology Pseudomass Tortous carotid arteries: may extend medially to appear in the Retropharyngeal space thus mimicking a mass lesion. These are well demonstrated on axial and coronal images. Carotid artery dissection/pseudo aneurysms These occur following a tear to the internal lining of the artery allowing blood to enter the arterial wall separating the intima from the media. This results in narrowing of the lumen of the artery. When the dissection extends beyond the intima a pseudoaneurysm forms. 264 Carotid Space IJV Thrombosis IJV thrombosis is usually secondary to central venous catheterization or IV drug abuse. On contrast enhanced CT the central portion of the IJV is hypodense with an enhancing wall. There may be an associated adjacent inflammation in relation to the vessel wall, manifested as fat stranding along the vessel wall. Lesions which may mimic a thrombosed vein are necrotic adenopathy, abscesses, infected brachial cyst. Coronal imaging or visualization of sequential axial images will clarify, as a thrombus extends craniocaudally as compared to focal lesions which are circumscribed.