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basal cell adenoma

Monday 8 March 2004

BCA; basal cell adenoma of the parotid gland; salivary basal cell adenoma

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Definition: Basal cell adenoma is an uncommon epithelial neoplasm of the salivary gland most commonly arising in the parotid glands. It presents as a slowly progressing, large parapharyngeal mass. Histopathology revealed a well-encapsulated mass with characteristic histomorphology.

A basal cell adenoma shows a well-circumscribed encapsulated, cellular and solid nodule.

Histologically, basal cell adenomas (BCA) are characterized by proliferation of basaloid cells in the absence of mesenchyme-like stromal component (present in pleomorphic adenomas).

The histologic subtypes include solid, trabecular, tubular, and membranous (also known as Dermal analogue tumor); combination of patterns is not uncommon.

A low power image of a BCA shows a sharply demarcated tumor composed of solid proliferation of basaloid cells surrounded by eosinophilic basement membrane like material.

Subtypes

The histologic subtypes of basal cell adenomas include solid, trabecular, tubular, and membranous type (also known as Dermal analogue tumor); combination of patterns is not uncommon.

This low power image shows encapsulated tumor with a jigsaw puzzle-like appearance formed by eosinophilic basement membrane like material separating the basaloid cell nests.

Basal cell adenomas are composed of two cell types : 1 – small cells with scanty cytoplasm and hyperchromatic nuclei at periphery of the cell island arranged in palisading manner and 2 - large polygonal cells with abundant cytoplasm and pale staining nuclei.

Squamous whorls may be seen occasionally. The stroma is composed of spindle shaped myoepithelial cells.

Solid basal cell adenoma is most common morphologic variant.

Microscopy

A basal cell adenoma is composed of two cell types – small cells with scanty cytoplasm and hyperchromatic nuclei at periphery of the cell island arranged in palisading manner and large polygonal cells with abundant cytoplasm and pale staining nuclei.

The stroma is composed of spindle shaped myoepithelial cells. Mitotic activity is not increased.

Basal cell adenoma can show anastomosing basaloid cell nests with a jigsaw puzzle-like appearance. The nests contain eosinophilic basement membrane-like material and are surrounded by hypocellular stroma containing a few myoepithelial cells.

This type of growth pattern may raise suspicion for adenoid cystic carcinoma. The presence of stromal myoepithelial cells serves as a clue. Stromal myoepithelial cells are absent in adenoid cystic carcinoma.

At High-power view, a basal cell adenoma can show clusters of basaloid cells separated by copious amounts of eosinophilic basement membrane-like material.

The basaloid cell nests can be separated by copious amounts of eosinophilic basement membrane-like material.

Basal cell adenoma can show a trabecular pattern of growth characterized by ribbon-like areas.

The intervening areas between the basaloid cell islands can show eosinophilic basement membrane-like material.

A basal cell adenoma can show small hyperchromatic cells with scanty cytoplasm at the periphery of the cell islands and larger polygonal cells with abundant pink cytoplasm and pale staining nuclei in the center.

The intervening areas between the basaloid cell islands show abundant eosinophilic basement membrane-like material.

Solid basal cell adenoma is the most common morphologic variant; however, it is not uncommon to see focal cystic areas with a solid tumor.

The treatment consists of complete surgical excision. The prognosis is excellent.

Recurrence may follow incomplete excision.

Malignant transformation is rare and shows highest association with membranous type of basal cell adenoma (as high as 28%).

Deposition of copious amounts of eosinophilic basement membrane-like material can create a peculiar pseudopapillary pattern.

Mucus-secreting goblet cells are sometimes seen in basal cell adenomas.

- Dermal analogue tumor

  • Dermal analogue tumor is a distinct variant of basal cell adenoma and is also referred to as membranous type of basal cell adenoma.
  • They are frequently multicentric and unencapsulated with a strong male predilection (>90% of cases occur in men).
  • Familial cases are associated with germline mutation of CYLD gene – a tumor suppressor gene on chromosome 16q12-q13. They may be associated with dermal cylindroma, trichoepithelioma, eccrine spiroadenoma and milia.
  • The classic low power appearance of a dermal analogue tumor is composed of a tumor cell islands separated by eosinophilic hyaline material mimicking dermal cylindroma.
  • The tumor is well circumscribed and covered by a thin capsule.
  • In contrast to classic basal cell adenomas, dermal analogue tumors are frequently multilobular and unencapsulated.
  • The histologic appearance is characterized by the presence of cell islands surrounded by thick eosinophilic membranes resembling a jigsaw puzzle.
  • The hyaline membrane material represents a reduplicated basal lamina which is diastase resistant and PAS-positive.
  • Mitosis and perineural invasion is usually absent.
  • Classic appearance of a dermal analogue tumor with islands of basaloid cells surrounded by copious amounts of eosinophilic basement membrane like material.

Differential diagnosis

The differential diagnosis of basal cell adenoma includes :
- pleomorphic adenoma
- adenoid cystic carcinoma

Images

- Basal cell adenoma

Localization

- parotid glands (mostly)
- minor salivary gland

Variants

- salivary basal cell adenoma with cribriform pattern

  • Cribriform type of salivary basal cell adenoma (cBCA) is relatively rare and problematic in distinction from adenoid cystic carcinoma (AdCC).
  • Good circumscription, lack of infiltrative properties, and absence of MMP9, laminin, CD117, and myoepithelial marker (SMA, S100 and calponin) in the cells around the cribriform spaces, are the most reliable points for differential diagnosis of cBCA from AdCC. (24206768)

Immunohistochemistry

- pancytokeratin+
- S-100+
- smooth muscle actin+ (myoepithelial cells)
- carcinoembryonic antigen+ (ACE+)
- vimentin+

Immunohistochemically, the epithelial cells are positive for low molecular weight cytokeratin, CEA and EMA.

The myoepithelial component is positive for p63, S100, calponin, actin and vimentin.

Bcl-2, c-kit, and nuclear beta-catenin reactivity may also be seen.

See also

- salivary tumors / salivary gland tumors