Page 78 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Cysts, Tumour-like Lesions and Response to Tissue Injury
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7.5 Necrosis
VetBooks.ir End-stage tissue injury that results in cell death.

Clinical features
• Necrosis in skin and subcutis is more frequently seen in association with:
• Fast-growing tumours.
• Haematoma/haemorrhage.
• Trauma to the adipose tissue.
• Necrosis is characterized by the loss of cytoplasmic and nuclear membrane integrity
leading to influx of water into the cells, denaturation of intracellular proteins and
digestion of the injured cells.
• Necrosis typically evokes a strong inflammatory response.

Cytological findings

• Cellularity: variable.
• Background: generally contains a large amount of basophilic amorphous material, which rep-
resents the cytoplasmic and nuclear debris of the dead cells. Cholesterol crystals may be present.
• When associated with neoplasia, variable numbers of neoplastic cells can be found amongst
the necrotic material. They may have a variable degree of degeneration and cellular details are
usually lost.
• There is often a background of lysed erythrocytes with products of red blood cell degrad-
ation, such as haemosiderin and haematoidin.
• Necrotic adipose tissue, when present, is characterized by collapsed adipocytes, which tend
to have more basophilic (blue-green) colour compared with viable adipocytes.
• Neutrophils and macrophages are frequently present in association with necrosis. Neutro-
phils are often degenerate, displaying nuclear and cytoplasmic swelling (karyolysis), also in
absence of infection. Macrophages often contain amorphous phagosomes.

Causes
• Hypoxaemia and ischaemia due to inappropriate tissue vascularization in fast-growing
tumours.
• Irritants.
• Trauma.

Pearls and Pitfalls
The centre of large and fast-growing masses is often necrotic. Hence, sampling from more
peripheral areas should increase the probability of obtaining a representative and diagnostic
sample.