CHAPTER V.. Diseases of Structures Enclosed Within the Mediastinum.

DISEASES OF STRUCTURES ENCLOSED WITHIN THE MEDIASTINUM.

The mediastinum is a space enclosed in the median plane of the thorax by the approach of the two opposite layers of pleura. Needless to say, at those points where the layers are in apposition, the space is theoretical only. It extends from the suprasternal region to the dorsal subvertebral region, and encloses all the vessels which pass from or to the base of the heart, the trachea, the œsophagus, the pneumo-gastric, diaphragmatic and cardiac nerves, etc., as well as the pericardial sac and the heart. The organs most frequently affected are the lymphatic glands lodged in the thickness of the mediastinum, the glands placed at the entrance to the chest, the bronchial glands, and the glands situated in the posterior mediastinum.

Inflammation of the mediastinum may coincide with inflammation of the mediastinal layers of the pleura; but this can only be detected on post-mortem examination. The lesions which can be recognised during life are simple inflammation of glands, resulting from pulmonary or pleural diseases, tuberculous inflammation of glands, and the presence of cancerous tumours of the mediastinum and hypertrophy of glands due to lymphadenitis.

Simple inflammation of the lymphatic glands is secondary and consecutive to broncho-pneumonia, verminous bronchitis, infectious bronchitis, etc.

It produces reflex irritation by compressing the pneumo-gastric and laryngeal nerves, and is indicated by loud, spasmodic coughing.

=Treatment= consists in administering iodide and bromide of potassium, terpine, in doses of 1 drachm per day for adults, essence of turpentine and tar water.

Tuberculous inflammation of glands, inseparable from pulmonary tuberculosis, has very special characteristics peculiar to tuberculosis.

Inflammation due to lymphadenitis is also very easy to diagnose as a rule, in consequence of the symmetrical enlargement of lymphatic glands elsewhere.

TUMOURS OF THE MEDIASTINUM.

Sarcomata, carcinomata, lymphomata, and lympho-sarcomata all occur in the mediastinum. They attack young healthy animals, and sometimes develop with such rapidity that in a few weeks they become generalised and invade the heart, lungs, and principal viscera. Their cause is as yet unknown.

=Symptoms.= At first sight the symptoms are much like those of pericarditis caused by foreign bodies. They consist in deformity of the presternal region, swelling of the jugulars, submaxillary œdema, irregular pretracheal tumefaction, etc.

The tumour, whatever its nature, commences in the mediastinum, develops towards the entrance to the chest, where it projects, and before long produces in the pretracheal region clearly marked œdematous swelling.

Between the two first ribs the tumour compresses the carotids, the jugulars, the nerve trunks, and also the trachea and œsophagus, producing difficulty in the return circulation, especially in the jugulars, swelling in the submaxillary space, loss of appetite and dyspnœa.

Palpation affords indication of a tumour of soft consistence, bosselated, more or less adherent to the skin, usually painless on pressure, and of irregular development. Compression of the œsophagus interferes with the deglutition of rough forage, impedes rumination, prevents eructation, and thus produces trifling but permanent tympanites.

The heart is affected reflexly or directly as a result of generalisation of the tumour, and the pulse may rise to 70 or even 120 per minute.

During the first stages neither auscultation nor percussion points to any pulmonary lesion. At a later stage the lung itself may be affected. The other important functions are normal.

Animals suffering from sarcoma, carcinoma, or lympho-sarcoma of the mediastinum waste very rapidly, lose appetite, become feverish, and soon develop cachexia.

=Diagnosis.= The diagnosis of tumour of the mediastinum is easy, because of the well-marked character of the apparent symptoms.

=Prognosis.= The prognosis must be regarded as extremely grave, and in most cases fatal, for there is no active method of intervention, extirpation being impossible.

There is no =treatment=. The animal should at once be slaughtered.