Page 278 - Feline diagnostic imaging

282 15 Thoracic Cavity
15.1.2 Rib Neoplasia
Tumors involving the ribs are one of the most common
sources of extrapleural mass lesions (masses that originate
outside the peripheral pleura). An extrapleural mass cre-
ates a broad‐based lesion with a convex margin facing the
lungs. The angle between the chest wall and mass should
be greater than 90°. These lesions typically grow inward
(toward the thoracic cavity) more than outward, and may
not be palpated or grossly visible. A secondary pleural effu-
sion is common with these lesions, and the chest wall
should be evaluated with care in patients with pleural effu-
sion of unknown etiology. Computed tomography is an
excellent imaging modality for a more detailed evaluation
of the ribs and pleural space in these cases.
The most common primary tumor affecting the ribs is
osteosarcoma. Other primary bone tumors occur rarely in
the cat (fibrosarcoma and chondrosarcoma), with no
reports of rib involvement [6,7]. Lysis and/or proliferation
are common, although secondary pleural effusion may
make visualization of the rib lesions more difficult early in
Figure 15.1 Cranial aspect of the lateral abdomen of a normal the disease process. Plasma cell tumor, as well as meta-
cat. The caudal ribs are visualized (10–13). Note that the costal static spread, can also result in lytic or proliferative rib
cartilages of the 13th ribs are free (floating ribs), while the costal changes [4]. Feline primary pulmonary adenocarcinoma
cartilages of ribs 10–12 unite to form the costal arch. The xiphoid has been reported to have local spread to the ribs
(*) is deviated ventrally; a normal variation. The adrenal glands
(white arrows) are mineralized; a normal variation in the cat. (Figure 15.5) [8].

(a)

(b)

Figure 15.2 Ventrodorsal (a) and lateral (b) thoracic images of a cat with left sided chest wall trauma. The left third rib appears to be
avulsed at the costochondral junction, and displaced caudally and laterally (arrows). Extensive subcutaneous emphysema is noted in
the adjacent soft tissues. The heart is shifted to the right, likely from prolonged right sided recumbency. A mild pneumothorax is
present, seen best on the lateral view (b). Source: Images courtesy of Dr Merrilee Holland.