Pilonidal cyst

Pilonidal cyst, also pilonidal disease, is benign (typically peri-anal) pathology. It is a common ditzel.

Pilonidal sinus redirects here.

General

• Benign.
• Young adults (late teens, early twenties) - usu. men.

Gross

• Usually at gluteal folds.
  • Uncommon: axilla, genital region, umbilicus, scalp.

Microscopic

Features:

• Cyst or pseudocyst into the deep dermis.
  • May be lined by squamous epithelium with inflammation +/-pseudoepitheliomatous hyperplasia.
• Neutrophils.
• Granulomatous inflammation.

DDx:

• Squamous cell carcinoma of the skin with inflammation.
• Infection.
• Hidradenitis suppurativa.

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Submitted as "Pilonidal Sinus", Excision:
- Consistent with pilonidal sinus.
- NEGATIVE for malignancy.

Block letters

SKIN LESION (PILONIDAL SINUS), EXCISION: 
- PILONIDAL SINUS.
- NEGATIVE FOR MALIGNANCY.

LESION (PILONIDAL SINUS), EXCISION:
- SKIN WITH PILONIDAL SINUS, CHRONIC INFLAMMATION AND SCARRING.
- NEGATIVE FOR MALIGNANCY.

Micro

The section shows hair-bearing skin with a deep sinus tract containing large clusters of neutrophils, abundant plasma cells, hemosiderin-laden macrophages, eosinophils and multinucleated giant cells. The core of the lesion is, focally, well-vascularized. At the edge of the lesion is fibrotic tissue with plump fibroblasts. Benign, fibrofatty tissue with scant inflammation completely surrounds the tract, in the plane of section; however, it is focally fragmented. There is no squamous lining within the sinus. No nuclear atypia is identified.

Alternate

The section shows hair-bearing skin with a deep sinus containing large clusters of neutrophils, abundant plasma cells, hemosiderin-laden macrophages and multinucleated giant cells. Benign fibrofatty tissue with scant inflammation completely surrounds the lesion in the plane of section. There is no squamous lining within the sinus. No nuclear atypia is identified.

Sinus versus cyst

The section shows hair-bearing skin with a cyst/sinus lined by benign squamous epithelium containing keratin. The surrounding dermis has a mixed inflammatory infiltrate, predominantly consisting of plasma cells and lymphocytes. Multinucleated giant cells are present. No significant nuclear atypia is identified.

See also

• Skin cysts.
• Ditzels.
• Perianal abscess.