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11

Advanced Imaging Modalities
Martha M. Larson

Department of Small Animal Clinical Sciences, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, VA, USA

11.1 Noncardiac Thoracic 11.2 Normal Anatomy
Ultrasound
Immediately beneath the transducer, on an intercostal
Ultrasound of the thorax is important as a supplemental window, lie the skin, subcutaneous fat, and thoracic wall
imaging modality to use in combination with thoracic radi- musculature [1–3]. Depending on the frequency of the
ographs in cats with pleural, mediastinal, chest wall, or transducer, these may be visualized more or less clearly.
pulmonary disease. There are limitations, as ultrasound is As in all situations, use the highest frequency transducer
unable to penetrate bone or gas interfaces. However, if pul- that will allow adequate penetration. A microconvex or
monary lesions are large or peripheral (minimal air sector transducer works best in limited intercostal win-
between lesion and chest wall), or pleural fluid is present to dows. Ribs are seen as symmetric bright curvilinear
act as an acoustic window, ultrasound visualization of tho- echogenic interfaces with a distal acoustic shadow. Deep
racic disease is possible. Ultrasound‐guided needle aspira- to the thoracic wall, the pleural surface forms a smooth,
tion or biopsy can allow a minimally invasive diagnosis, linear, echogenic band (Figure 11.1). Everything deep to
precluding the need for thoracotomy. Ultrasound can also the pleural surface (interface with lungs) is a shadow, with
be used to guide thoracocentesis. Ultrasound may detect diffuse speckled echoes, reverberation, and occasional
small volumes of pleural fluid or small mediastinal masses comet tail artifacts. In normal patients, the lung may be
not visualized radiographically, and can also be used to seen to glide back and forth with respiration. This gliding
rule in or rule out pleural effusion or mediastinal mass sus- motion can help to differentiate pulmonary masses from
pected based on radiographs. chest wall or mediastinal lesions.
Several ultrasound windows can be used, with the The normal mediastinum can be difficult to evaluate due
patient in dorsal, lateral, or sternal recumbency. If the to surrounding air‐filled lungs and the presence of fat.
patient is in respiratory distress, sternal recumbency or However, if pleural effusion is present, normal mediastinal
even standing or sitting may be the least stressful position. tissues are better visualized (Figure 11.2). Large, anechoic
An intercostal window (between ribs) is commonly uti- vessels extend toward the thoracic inlet in the cranial medi-
lized for thoracic evaluation, with both short axis (image astinum. Mediastinal and pericardial fat appear echogenic,
plane parallel to ribs) and longitudinal/dorsal (image plane coarse, and unorganized, and do not resemble a smooth
transverse to ribs) images made. The cranial mediastinum mass. An intercostal or possibly thoracic inlet approach is
can be evaluated for masses using a ventral and cranial best for evaluating the cranial mediastinal area. Normal
(parasternal) window. Caudal lung and diaphragm lesions mediastinal lymph nodes are usually not well visualized.
may be evaluated using a subcostal window. With this Pleural fluid creates an excellent window for mediastinal
approach, the liver is used as a window to the caudal tho- evaluation, allowing some normal structures to be seen.
rax. Dependent pleural fluid (with the patient in lateral, The diaphragm is typically evaluated from a subcostal
sternal, or dorsal recumbency) can be utilized to create approach, and appears as an echogenic, curvilinear line on
a window for evaluation of the lungs, chest wall, and the cranial margin of the liver (where it represents the
mediastinum. lung–diaphragm interface). The diaphragm is seen as a

Feline Diagnostic Imaging, First Edition. Edited by Merrilee Holland and Judith Hudson.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.