Page 212 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

Chapter 16 · Surgery of the mediastinum

Organ Region polyuria and polydipsia, and focal or generalized myas-
thenia gravis associated with mediastinal thymoma. A
VetBooks.ir Craniodorsal Cranioventral Middle Caudodorsal Caudoventral be associated with mediastinal disease.
wide variety of non-specific clinical signs can, therefore,

Cranial vena cava + Evaluation of the mediastinum
Aortic arch + Physical examination of the mediastinum is limited to estab-
Mediastinal lymph nodes + lishing the compressibility of the cranial thorax, and to
thoracic auscultation. Abnormalities found using these
Trachea + + +
physical examination techniques are not specific to media-
Oesophagus + + + stinal disease. Diagnostic imaging techniques including
Thoracic duct + + survey and contrast radiography, ultrasound examination
and endoscopy are non-invasive steps that may be neces-
Brachycephalic trunk +
sary to characterize mediastinal disease. Advanced imaging
Left subclavian artery + techniques such as computed tomography (CT) and mag-
Thymus + netic resonance imaging (MRI) are being used increasingly
Sternal lymph nodes + to provide more specific information about the rel ationship
of mediastinal neoplasia, in particular, to other structures
Mainstem bronchi +
contained within the mediastinum (Fujimoto et al., 1992;
Heart + Pirronti et al., 2002). For tissue diagnosis or collection of
Right and left phrenic nerves + + + samples for culture or biochemistry, more invasive tech-
niques such as ultrasound-guided fine-needle aspiration or
Pulmonary arteries and veins +
core tissue biopsy and surgical exploration are required.
Tracheobronchial lymph nodes +
Broncho-oesophageal arteries and veins + Radiography
Descending aorta + +
In the absence of disease the mediastinum is an unclear
Principal bronchi + radiographic anatomical region that lacks contrasting
Right and left vagus nerves + tissue densities except for the air-filled trachea. The cranio-
ventral region is more radiopaque because it is thicker.
Azygos vein + +
The craniodorsal and caudodorsal regions of the media -
Caudal vena cava + stinum are best viewed using a combination of ventro-
Location of organs and structures ithin the five regions of dorsal (VD) and dorsoventral (DV) radiographic views
16.3 the mediastinum. + = present. (Brinkman et al., 2006; Kirberger and Avner, 2006). Caudal
(Adapted from Thrall (2002))
mediastinal masses can be highlighted on DV views by the
contrasting adjacent pulmonary parenchyma and magnifi-
cation (Kirbeger and Avner, 2006). Similarly, a DV view can
allow improved definition of the cranial mediastinum when
Clinical features of mediastinal compared with a VD view, owing to better inflation of the
disease cranial pulmonary cupula. In the normal patient the media-
stinum is no wider than twice the width of the thoracic
Diseases of the mediastinal structures may cause acute spine, although in obese animals the craniodorsal region
clinical signs such as regurgitation associated with an may become wider owing to the accumulation of fat. The
oesophageal foreign body (see Chapter 9) or dyspnoea middle region of the mediastinum is best viewed on a
associated with traumatic intrathoracic tracheal avulsion lateral view. In young dogs the thymus is viewed as a trian-
(see Chapter 13). Other neoplastic or inflammatory condi- gular structure in the cranioventral region of the media-
tions of the mediastinum are associated with vague clini- stinum, often referred to as the thymic sail (Figure 16.4).
cal signs such as pyrexia, weight loss, reduced appetite Four general radiographic observations are made in the
and malaise. Such disease processes may also affect the presence of disease: mediastinal shift, pneumomedia-
recurrent laryngeal nerves (causing laryngeal paralysis) stinum, mediastinal fluid and mediastinal masses. Media-
the vagosympathetic trunk (causing Horner’s syndrome) stinal shift occurs secondary to a unilateral increase or
and may compress the oesophagus, trachea and major decrease in lung volume or secondary to the presence of an
vessels resulting in regurgitation, coughing and dyspnoea intrathoracic mass. Mediastinal shift generally does not indi-
and either cranial or caudal venous hypertension and cate disease of the mediastinum but disease in the lungs,
oedema (cranial or caudal caval compression syndrome). bronchi, thoracic wall or pleura. Pneumomediastinum is the
Because of the anatomy, diseases affecting the media - accumulation of free gas within the mediastinum; this pro-
stinum may extend into the neck or abdomen (and vice vides contrast and enhances the outer walls of mediastinal
versa), along the continuous fascial planes. Cervical structures such as the trachea, oesophagus and great
oesophageal perforation can, therefore, lead to septic vessels. Pneumomediastinum is best observed on a lateral
mediastinitis; conversely, intrathoracic tracheal injury radiograph, as the width of the mediastinum is not signif-
may lead to cervical and subcutaneous emphysema. In icantly increased. The source of air may be the trachea,
cats, a large mass occupying the cranial mediastinum will mainstem bronchi, marginal alveoli or oesophagus.
often reduce the compressibility of the cranial rib cage. In Ex tension of gas from the cervical region caudally or from
addition, some mediastinal neoplasms are associated the retroperitoneum cranially into the mediastinum may
with paraneoplastic syndromes such as the hypercal- occur. Pneumomediastinum occasionally progresses to a
caemia occasionally associated with lymphoma, causing pneumothorax, especially in trauma cases or when large

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