Cutaneous masses

Hernias

Swelling that pits on pressure

Emphysema

Abscesses/cellulitis

Urticaria

Involves the head

Bacterial granulomas

Urticaria

A non-painful and non-pitting accumulation of serum under the skin

Trauma

Horses

An epithelial-lined cavity containing fluid or solid material

Reaction to infection/inflammation

'Needle only' with no suction

Cell types and diagnostic representation

When tissue architecture is needed

Unrepresentative samples and inability to grade neoplasms

Potential causes of non-infectious inflammatory masses in the skin include urticaria/angioedema, eosinophilic granuloma, insect bite granuloma, sterile panniculitis, hematoma, and seroma.

Potential causes of infectious inflammatory masses in the skin include abscesses/cellulitis (post-trauma or foreign body/bite), furunculosis, bacterial granulomas (such as those caused by Mycobacteria, Actinobacillus, or Nocardia), and deep/subcutaneous or systemic fungal granuloma.

Urticaria is characterized by wheals with or without pruritus, while angioedema is characterized by large, edematous swelling usually involving the head.

The main cause of cellulitis in pigs is interdigital staphylococcal furunculosis.

Furunculosis can be caused by Staphylococcus or Demodex infections.

Angioedema involves degranulation of mast cells causing painless and pitted swelling upon pressure.

Gas in the subcutaneous tissue that is crepitant without pain or swelling can be caused by severe respiratory disease or lung puncture, introduction of air through a cutaneous wound, rumenotomy or rumen cannulization, or Clostridial infections.

A seroma is an accumulation of serum under the skin, while a hematoma is a loss of blood from damaged or ruptured blood vessels under the skin.

In older animals, neoplastic skin masses are commonly caused by conditions such as melanomas in grey horses, lipomas, sebaceous adenomas, and mast cell tumors.

Some factors to consider include species (mast cell tumors are common in older dogs), breed/color (mast cell tumors are common in boxers), and age (neonates may have umbilical abscess, while older animals may have neoplasia).

History of trauma/fight/surgery may indicate abscess, cellulitis, hematoma, or seroma. Recent injection may indicate abscess or panniculitis. Systemic signs such as respiratory signs, weight loss, lethargy may indicate systemic/metastatic neoplasia or systemic fungal infections. Depression and inappetance may be associated with microbial infections/abscess. Dermatological history, such as speed of onset of mass or prior history of neoplasia, may also be relevant.

Clinical signs that may indicate a mast cell tumor in a dog include paraneoplastic signs (e.g. hematemesis), respiratory signs, weight loss, lethargy, depression, and inappetance.

During a dermatological examination of a skin mass, it is important to consider the presence of inflammation (sterile vs septic), the type of neoplasia (round cell vs epithelial vs spindle cell), and the characteristics of a cyst (contents produced by cyst's epithelial lining and presence of secondary inflammation if cyst ruptures).

Some limitations of cytology in investigating skin masses include the fact that not all cell types are easily shed, making the sample unrepresentative or non-diagnostic. Cytology also does not provide information about tissue architecture, so subsequent histopathology may be required for grading a neoplasm.

Cytology of a skin mass involves techniques such as fine needle aspirate (needle only, continuous suction, or intermittent suction) and impression smear of the surface or sinus contents.