Exercise 19 discussion

Clinical history and questions

Specimen from a 6 week-old foal that was believed to have received insufficient colostrum at birth.  During its short life it suffered a range of febrile episodes, including destructive osteoarthritis of a hock joint that necessitated euthanasia.

1.  Describe the abnormalities.

2.  What basic disease processes might be present?

3.  Pathological diagnosis (give other possibilities in order of preference)?

4.  Outline the likely pathogenesis of this condition.

An interpretation of Diagnostic Exercise No. 19 – Roger Kelly


Thoracic content, viewed from left side.  Anteriorly and ventrally, the pleural surface of the left lung bears an interanastomosing pattern of narrow sunken channels.  These are more extensive ventrally, and their floors are darker in colour than the surrounding aerated lung, from which they are sharply demarcated

Basic disease process/es:

There is no evidence of hyperaemia, fibrinous or fibrous adhesions, or of necrosis or haemorrhage.  The sunken lung is clearly empty: no air or exudate, or anything else.  By default, the condition is (at this stage) degeneration, since none of the other basic processes (inflammation, developmental defect or neoplasia) appear to be operating.

Morphological diagnosis:

Pulmonary atelectasis.  Atelectasis may be the result of a developmental disorder (under-inflation at birth), but the history and pattern suggests otherwise (see below).

Outline of the probable pathogenesis:

Pulmonary atelectasis can be caused by 1) a space-occupying, compressive process in the thorax; 2) congenital hypo-inflation (often compounded by deficiency of surfactant; eg in prematures); 3) absorption of fluid or inflammatory exudate such as might occur in the healing stages of exudative pneumonia, and 4) ventilation-perfusion mismatching in lowermost lung in animals recumbent for long periods and performing reduced respiratory excursions (eg, during prolonged anaesthesia).

Of these, 3) seems most likely, since affected lung has the same distribution as does bronchopneumonia, and this colostrum-deprived foal would have been a good candidate for a severe respiratory infection.  Presumably the animal survived the exudative phase of the disease, and complete healing and reinflation of the lung might have been achieved, since there seems to be no significant scarring.  So this is a case of post-pneumonic atelectasis.

Please contact me roger-kelly@aapt.net.au if you want to discuss any aspect of this case.