June 2011

Case A (Canine parvovirus enteritis)

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Tissues from a 16-week-old dog with vomiting and diarrhoea.

Example histopathological description

The section includes small intestine and mesenteric lymph node.  In the deep intestinal mucosa, the crypts are mostly absent; those remaining are lined by irregular epithelial cells that are cuboidal, rounded or flattened and contain prominent nuclei with single or multiple nucleoli. Some of the crypts are dilated and some contain degenerate cellular debris or fibrin. The associated lamina propria has collapsed and there is scattered fibrosis, haemorrhage, fibrin deposition and a moderate lympho-histiocytic infiltration. Towards the luminal surface, there is a layer of degenerate neutrophils which demarcates the superficial mucosa which has extensive coagulative necrosis of villi and many bacterial colonies. The sub-mucosa and muscularis are moderately oedematous with dilated lymphatics and expanded intercellular spaces. The muscularis also has moderate patchy haemorrhage. The mesentery has moderate vascular congestion and some haemorrhage.

The section of mesenteric lymph node is not connected to the intestinal section. The subcapsular and medullary sinuses are markedly expanded. The medullary sinuses, in particular, have marked accumulations of erythrocytes. The cortex is moderately depleted of small lymphocytes.

Morphologic diagnoses

Enteritis, necrotising, acute, diffuse, severe, with subacute crypt necrosis.

Mesenteric node lymphoid depletion, subacute, diffuse, moderate

Aetiological diagnosis

Canine parvovirus enteritis

Differential diagnosis

Other bacterial infections such as salmonellosis, clostridial enteritis, campylobacteriosis, Citrobacter freundii infection, yersiniosis and colibacillosis should be considered, as well as cytotoxic chemicals (notably chemotherapeutic agents), ionising radiation, canine distemper or canine minute virus infection, infectious canine hepatitis, coronavirus or rotavirus infection, and heavy metal toxicity.

Case B (Ovine Brucellosis)

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Lesion found during fertility evaluation of a ram.

Example histopathological description

In this section of epididymis, the ductus epididymis is ectatic and tubules are filled with abundant, disintegrating spermatozoa admixed with scattered neutrophils, macrophages, rare multinucleated giant cells, and sloughed epithelial cells. The lining epithelium is variably hyperplastic and in some areas there is loss of apical cilia and squamous metaplasia.  There is widespread individual epithelial cell necrosis and transmigration of the tubular epithelium by neutrophils and lymphocytes, with multifocal small microabscesses and occasional intraepithelial lumina formation.  There is mild to moderate concentric periductal fibrosis with mild oedema and patchy interstitial infiltrates of lymphocytes, plasma cells and a few macrophages.

Morphological diagnosis

Epididymitis, chronic, diffuse, mild to moderate with ductal ectasia, hyperplasia and squamous metaplasia.

Differential Diagnosis

Differential considerations should include infection with Actinobacillus seminisHistophilus somni andBrucella ovis (in which there would normally be a more severe pyogranulomatous inflammatory response).  Bacteria that may be involved in ascending infections include Escherichia coli, Mannheimia haemolytica and Arcanobacterium pyogenes.  Congenital segmental aplasia of mesonephric duct derivatives with secondary spermiostasis could also be considered.