Page 75 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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7.4 Haematoma and Haemorrhage
VetBooks.ir A haematoma is an abnormal collection of blood outside a blood vessel secondary to haemor-

rhage. Haemorrhage is an escape of blood from a ruptured blood vessel.

Clinical features
• Organizing haematoma appears as a discrete cutaneous and subcutaneous mass.
It can be cavitated and often contains variable amounts of blood.

Cytological features
• Cytological findings depend on the time of onset of the haematoma/haemorrhage at the
time of sampling:
• Peracute haemorrhage (few hours from extravasation):
• Background: numerous intact red blood cells with/without platelets.
• Acute haemorrhage (> 12–24 hours from extravasation):
• Background: numerous intact red blood cells (platelets will be dissolved by this time)
• Macrophages displaying erythrophagocytosis: intact red blood cells are seen within
the cytoplasm of macrophages.
• Chronic haemorrhage (> 24–36 hours from extravasation):
• Background: numerous red blood cells, intact or lysed. Cholesterol crystals may
form secondary to the erythrocyte membrane dissolution.
• Macrophages containing the degradation products of the red blood cell breakdown
(haemosiderin and/or haematoidin crystals). Haemosiderin appears as dark
basophilic-black granules of variable sizes, always within the cytoplasm of the
macrophages. Haematoidin crystals are typically rhomboid and yellow/orange.
They may be found in the macrophages or occasionally scattered in the background.
• As the lesion starts to organize, macrophages increase in number and reactive fibroblasts
are often seen. Other inflammatory cell types may also be present.
Causes

• Trauma.
• Vascular neoplasms (haemangioma and haemangiosarcoma) or any other poorly exfoliative
neoplasms associated with local haemorrhage.

Differential diagnosis
Vascular neoplasms