Pilomatricoma

Author: Mikael Häggström

Histopathology of pilomatricoma, high magnification, H&E stain, showing the characteristic components.

Low magnification, also revealing foreign body giant cells and calcifications, which are also common within pilomatricomas..

Pilomatricomas generally present as skin cysts.

Microscopic evaluation

The characteristic components of a pilomatricoma include a stroma of fibrovascular connective tissue surrounding irregularly shaped, lobulated islands containing basaloid cells (being darkly stained, round or elongated, with indistinct cell borders and minimal cytoplasm, with nuclei being round to ovoid, deeply basophilic and generally prominent nucleoli), which abruptly or gradually transitions into ghost cells (having abundant, pale, eosinophilic cytoplasm, well defined cell borders and a central clear area, but only only faint traces of nuclear material), which in turn may transition into keratinaceous to amorphous necrosis.

Differential diagnoses

Mainly:

• 

  Epidermoid cyst, having the following typical findings:
  - Stratified squamous epithelium with a granular layer
  - Cyst wall does not contain eccrine glands, sebaceous glands or hair follicles
  - Abundant keratin flakes in cyst lumen
  - Often giant cell granuloma in ruptured cysts, similar to foreign body granuloma.

• 

  Trichilemmal cyst, containing, from external (top) to internal (bottom):
  - Fibrous capsule
  - Small, cuboidal, dark-staining basal epithelial cells in a palisade arrangement, with no distinct intercellular bridging
  - Swollen pale keratinocytes, which increase in height closer to the interior
  - Solid eosinophilic-staining keratin
  There is no granular cell layer (in contrast to an epidermoid cyst).

Further information: Skin cyst

Microscopic report

Preferably brief:

Right cheek skin, excision: Pilomatricoma

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