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15

Thoracic Cavity
Martha M. Larson

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

15.1 Thoracic Cavity likely due to the anatomic shape and resilience of the feline
thorax [4]. Rib fractures secondary to trauma are most
The overall shape of the feline thorax appears somewhat often located in the midbody or dorsal aspect of the rib,
shallower and relatively longer than in the dog. The ribs with variable rib(s) affected, depending on the location of
and sternebrae surround and protect the thorax laterally the trauma (Figure 15.2). Widened intercostal spaces may
and ventrally [1–3]. Thirteen pairs of ribs are normal, but be present with displaced rib fractures, avulsions, or inter-
variations in number or symmetry are common. Ribs 1–9 costal muscle injury. Less obvious rib trauma includes
join with the sternum via the costal cartilages. The costal avulsion of the rib at the costospinal junction, costosternal
cartilage of the first rib articulates directly with the manu- junction, or costochondral junction [3]. Flail chest is a spe-
brium; costal cartilages 2–9 articulate with cartilage cific type of traumatic rib fracture, and occurs when at
between the sternebrae. The costal cartilages of ribs 10–12 least two consecutive ribs are fractured both dorsally and
unite to form the costal arch ventrally and laterally, while ventrally, resulting in an independent wall segment. This
the cartilages of the 13th ribs are considered floating, or segment demonstrates paradoxical movement with respi-
free (Figure 15.1). In some cats, the costal cartilages appear ration, moving inward with inspiration and outward with
fragmented, or incomplete. This is a normal variation. The expiration. Flail chest is most often associated with more
13th ribs may be smaller than normal, or one or both may severe trauma, so concurrent pulmonary contusions, pleu-
be absent. There are normally eight sternebrae in the cat. ral effusion, and/or pneumothorax may be present
The first sternebra is the manubrium, which appears more (Figure 15.3).
prominent than in the dog. The xiphoid process (last stern- Nontraumatic rib fractures have been reported in a num-
ebra) is longer and narrower than in the dog, and is contin- ber of conditions, most commonly secondary to chronic
ued caudally by the xiphoid cartilage. While eight respiratory or cardiac disease, coughing, or sneezing [4,5].
sternebrae are normal, congenital abnormalities in num- Chronic increased respiratory rate and effort lead to
bers are common and typically of no clinical significance. increased work of breathing, and subsequent increased
Sternebrae may be fused or decreased in number. mechanical stress and muscle fatigue, all of which can lead
to rib fracture [4]. Unlike traumatic rib fractures, nontrau-
matic fractures are most commonly noted in the midbody
15.1.1 Diseases of the Ribs of the 9th–13th ribs [4]. These caudal ribs are involved in
15.1.1.1 Fractures greater respiratory excursions and therefore subject to
Rib fractures are most often associated with trauma, and greater mechanical stress (Figure 15.4). Rib fractures may
should be carefully assessed on thoracic images taken after also be pathologic in nature, secondary to infections,
a traumatic incident. They are not as common in cats, primary, or metastatic neoplasia.

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