Page 720 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Respir atory system: 3.4 Medical conditions of the lower respir atory tr act 695

VetBooks.ir methenamine silver stain can be helpful in achieving and hyperglobulinaemia. Deviation of the trachea
or mainstem bronchi may be observed endoscopi-
a diagnosis. The prognosis for affected foals is poor,
but treatment with trimethoprim/sulphonamide
combinations may be effective. cally, resulting from external compression of these
structures by the abscess. With advancement of
cranial mediastinal masses, jugular distension may
MEDIASTINAL ABSCESSATION be present. Transthoracic ultrasonography may
reveal pleural effusion, which is frequently present
Definition/overview in horses with mediastinal masses. Typically, medi-
Mediastinal abscessation is uncommon. Abscessation astinal masses cannot be viewed by transthoracic
may develop from translocation of bacteria via the ultrasonography due to interruption of the ultra-
bloodstream into mediastinal lymph nodes from sound waves by overlying aerated lung. However,
the lymphatic system during pleuropneumonia, or ultrasonography at the thoracic inlet may allow
through extension of infection from a neck or chest visualisation of a mediastinal mass and charac-
wound. Metastatic Streptococcus equi infection (bas- terisation of its contents (Fig. 3.154). Ultrasound
tard strangles) can also cause mediastinal masses. guidance is also useful for obtaining centesis sam-
ples for cytology and culture. Thoracic radiogra-
Aetiology/pathophysiology phy is frequently useful in identifying the presence
Streptococcus equi and Rbodococcus equi are most fre- of a mediastinal mass. Thoracocentesis to drain
quently associated with mediastinal abscesses in pleural effusion is important prior to chest radiog-
horses, although Aspergillus sp. was isolated from a raphy to optimise visualisation of thoracic masses.
mediastinal granuloma in one horse. During pleu- Computed tomography (CT) may be useful to
ropneumonia, lymphatic drainage of bacteria to confirm the location and identify associated struc-
bronchial lymph nodes may lead to mediastinal tures of mediastinal abscesses in foals.
abscessation. Penetrating wounds to the neck and
chest, or rupture of the oesophagus, may also lead
to infection of the mediastinum, with subsequent
abscess formation as infection localises. 3.154

Clinical presentation
Clinical presentation will vary with the inciting
cause. Specific signs of mediastinal abscessation may
not be obvious when concurrent pleuropneumonia
or severe wounds are present. When mediastinal
abscessation is the primary problem, non-specific
signs of weight loss, inappetence and intermittent
fever are common. Tracheal compression may result
in progressive inspiratory impairment. Laryngeal
dysfunction may occur from damage to the recur-
rent laryngeal nerve.

Differential diagnoses Fig. 3.154 Cranial mediastinal mass in an adult
Mediastinal lymphadenopathy, neoplastic mass or a horse. A 28-year-old gelding presented with a
cyst should be considered. history of progressive exercise intolerance, pitting
oedema of the chest and ventral cranial thorax and
Diagnosis bilateral distension of the jugular veins. Thoracic
Clinical signs are non-specific. Chronic inflam- ultrasonography revealed the presence of a circular
matory haematological changes include anaemia, mixed echogenicity 12 × 16 cm thoracic mass cranial
leucocytosis with neutrophilia, hyperproteinaemia to the heart (yellow + markers and lines).