Page 117 - Atlas of Small Animal CT and MRI

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Lymph nodes

Introduction Lymphography has been used in experimental studies
to determine lymph flow from regions of the head to
The lymph nodes of the head include the facial, parotid, sentinel lymph nodes using CT and MR. This may be a
5,6
mandibular, and lateral and medial retropharyngeal lymph useful technique to trace potential routes of metastasis
nodes. These lymph nodes drain the head and oral cavity, in head and neck cancer.
and the mandibular and medial retropharyngeal lymph
nodes are routinely evaluated on CT and MRI scans for
signs of abnormality. Lymph from the rostral lymph nodes Inflammatory disorders
passes through the lymph node chain sequentially and Lymph nodes affected by regional disease, such as
may mix and cross to the contralateral side before reach- abscesses, myositis, otitis externa, and other inflamma-
ing the medial retropharyngeal lymph nodes. 1 tory disorders, undergo hyperplasia as part of the immune
The mandibular lymph node group consists of three response. On CT and MR images, the lymph nodes
to four lymph nodes surrounding the facial vein on the appear mildly to moderately enlarged. On CT, reactive
ventral neck and are, in aggregate, 10–25 mm in length lymph nodes are normally iso attenuating to hypoattenu-
(Figures 1.8.1, 1.8.3). The parotid lymph nodes (one or ating on unenhanced images and moderately to strongly
two nodes) are located lateral to the temporomandibu- contrast enhancing with a uniform or central pattern
lar joint, medial to the parotid salivary gland and are (Figure 1.8.5). Lymph nodes are similarly mildly to
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detected infrequently on CT and MR images. The moderately enlarged on MR images with homogeneous
medial retropharyngeal nodes are located between the to heterogeneous contrast enhancement. The parotid
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mandibular salivary gland and common carotid artery and lateral retropharyngeal lymph nodes may be visible
and are 30–70 mm in length in dogs and average when enlarged. In severe cases, lymph nodes may become
2,3
20.7 × 4.2 × 13.1 mm in cats (Figures 1.8.2, 1.8.4). The abscessed with central hypoattenuating regions and
lateral retropharyngeal lymph nodes are less frequently peripheral contrast enhancement (Figure 1.8.6).
seen in normal animals. Reactivity may also cause poor margination and soft‐
Lymph nodes are isoattenuating to muscle on CT and tissue stranding in surrounding fat.
strongly contrast enhance. They are hypointense to fat
and isointense to muscle on T1 images and hypo intense
to fat and hyperintense to muscle on T2 images. Lymph Neoplasia
nodes are isointense to fat on contrast‐enhanced T1 Neoplasia of the head and oral cavity may metastasize
images. The lymph nodes of the head are generally less to the regional lymph nodes. The mandibular and medial
4
than 5 mm in width. In the caudal part of the neck, the retropharyngeal lymph nodes should be evaluated for
superficial cervical lymph nodes are located lateral to enlargement, heterogeneity, and change of shape to
the serratus ventralis and scalenus muscles. detect metastatic disease (Figures 1.8.7, 1.8.8, 1.8.9).

Atlas of Small Animal CT and MRI, First Edition. Erik R. Wisner and Allison L. Zwingenberger.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
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