Page 211 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 16
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Surgery of the mediastinum

Daniel J. Brockman and Arthur K. House

Anatomy delicate nature frequently allows extension of disease from
one side of the chest to the other. In the cranial thorax, the
The mediastinum is the potential space between the right mediastinum is just to the left of the midline; the media stinal
and left pulmonary pleural sacs that, in the normal dog or pleura joins the costal pleura to form the pleural cupula,
cat, contains the: which extends cranially beyond the first rib on each side.
The cranial mediastinum (Figure 16.1) communicates with
• Heart fascial planes of the neck. In the caudal thorax, the media-
• Great vessels stinum is continuous with the pericardium and resides to
• Trachea the left of the midline to accommodate the accessory lung
• Oesoph agus lobe. It attaches to the left side of the diaphragm, contact-
• Lymph nodes ing the left thoracic wall near the ninth costochondral junc-
• Thymus.
tion to form the sternopericardial ligament. Caudally, the
Occasionally, ectopic thyroid and parathyroid tissue mediastinum communicates with the retroperitoneal space
resides within the media stinum. The thoracic spine forms through the aortic hiatus. The caudal vena cava resides in a
the dorsal mediastinal border and the sternum forms the reflection of the parietal pleura, the plica venae cavae, on
ventral border. The cranial and caudal borders are formed the right side of the mediastinum (Figure 16.2). To assist
by the thoracic inlet and diaphragm, respectively. The lateral radiographic interpretation, the mediastinum is divided into
borders are formed by the mediastinal or parietal pleura, five regions: craniodorsal, cranioventral, middle, caudo-
which sep arate one hemithorax from the other. Although dorsal and caudoventral. Structures contained within each
the media stinal pleura is not truly ‘fenestrated’ tissue its region are outlined in Figure 16.3.

Aorta Accessory
lung lobe
Oesophagus Oesophagus
Mediastinal
Longus colli pleura
muscles
Left subclavian
artery
Trachea
Caudal
vena cava
Brachycephalic
trunk

Costal
pleura
Cranial
vena cava Mediastinal
pleura Plica venae Diaphragm
cavae
A computed tomographic section (bone window) through the A computed tomographic section (lung window) through the
16.1 16.2
cranial thorax of a dog, cranial to the heart. The mediastinum caudal thorax of a dog, caudal to the heart. Note the vena
at this level contains the cranial vena cava, trachea, longus colli muscles, cava residing in a reflection of the parietal pleura hich forms the plica
oesophagus and primary branches of the aorta such as the venae cavae. The mediastinum attaches to the left side of the diaphragm
brachycephalic trunk, right subclavian artery and left subclavian artery. near the ninth costochondral junction to accommodate the accessory
The thymus is not visible in this dog. lung lobe situated in the right hemithorax.

202 BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, second edition. Edited by Daniel J. Brockman, David E. Holt and Gert ter Haar. ©BSAVA 2018

Ch16 HNT.indd 202 31/08/2018 13:32