Introduction

In the normal adult neck there may be up to 300 lymph nodes, ranging in size from 3 mm to 3 cm. It is an understatement to say that the anatomy and its various associated classifications, groupings, subgroupings and, more recently, levels, is complex. The radiologist who decides to ignore the subtleties and complexities of the lymphatics of the head and neck region will not be alone. Yet, if one wishes to examine the head and neck region, one cannot ignore the lymphatic system. Many pathologies in the head and neck region present as a palpable lymph node. Most cervical lymph nodes are within 1–2 cm of the skin surface, and the superior resolution of ultrasound now allows the morphology and blood flow characteristics of lymph nodes to be clearly defined. Its resolution is superior to anything that computed tomography (CT) or magnetic resonance imaging (MRI) can currently offer.

Anatomy

Lymph nodes are small, oval or reniform bodies, typically 0.1–2.5 cm long, lying in the course of lymphatic vessels. There is usually a small indentation on one side, the hilum, through which blood vessels enter and leave and from which the efferent lymphatic also emerges (Figure 4.1). Multiple afferent lymphatics drain into the outer cellular cortex of the node; lymph then enters a labyrinth of lymphatic channels within the node.