Skin nonmelanocytic tumor

Adnexal tumors

Hair follicles


Last author update: 25 July 2023
Last staff update: 25 July 2023

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PubMed Search: Pilomatricoma

Saira Fatima, M.B.B.S.
Nasir Ud Din, M.B.B.S.
Page views in 2023: 71,329
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Cite this page: Fatima S, Ud Din N. Pilomatricoma. website. Accessed February 23rd, 2024.
Definition / general
  • Pilomatricoma is a benign skin adnexal tumor originating from hair matrix and cortex
Essential features
  • Benign skin adnexal tumor originating from hair matrix and cortex
  • Most commonly occurs in head and neck, extremities and trunk in children
  • Grossly appears as circumscribed hard dermal tumor with cheesy material
  • Most cases behave indolently without recurrences
  • Pilomatrixoma
  • Calcifying epithelioma of Malherbe (not recommended)
ICD coding
  • ICD-O: 8110/0 - pilomatrixoma, NOS
  • ICD-11: 2F22 & XH9E37 - benign neoplasms of epidermal appendages & pilomatricoma, NOS
  • Pilomatricoma, being the most common adnexal neoplasm in children, favors young age (Actas Dermosifiliogr 2010;101:771)
    • However, a wide age range has been described from 3 months to 93 years
  • Females are affected slightly more than males
  • Usually solitary but multiple lesions can occur (Int J Dermatol 2017;56:1032)
  • Pilomatricoma development is associated with mutations in CTNNB1 gene located in the exon 3 region encoding beta catenin, a 92 kDa molecule involved in cell - cell adhesion
  • As an integral component of Wnt signaling pathway, beta catenin monitors cell proliferation, differentiation and survival
  • Beta catenin expression in hair matrix during human embryogenesis signifies its importance in hair follicle development and thus pilomatricoma origin
  • BCL2 oncoprotein is also implicated in its development (Arch Pathol Lab Med 2014;138:759)
Clinical features
  • Generally very hard, owing to calcification; skin lesions that are calcified tend to display positive teeter totter and tent signs
    • Teeter totter sign is observed when applying downward pressure to one end of the lesion causes the other end to spring upwards in the skin
    • Tent sign appears when the skin overlying the lesion is stretched, revealing multiple facets and angles, resembling a tent
  • Clinical examination alone may not be diagnostic (Am J Dermatopathol 2018;40:631)
    • Imaging studies ultrasound, computed tomography and magnetic resonance imaging are helpful; ultrasonography has a high positive predictive value (95.56%) (Arch Craniofac Surg 2020;21:288)
Radiology description
  • Ultrasound
    • Pilomatricoma present as heterogeneous, well demarcated, hypoechoic mass between the deep dermis and the subcutis on ultra high frequency ultrasonography
    • Most common features are internal echogenic foci (calcifying), hypoechoic rim and posterior shadowing (J Ultrasound 2008;11:76, Front Med (Lausanne) 2021;8:673861)
  • CT scan
    • Appear well demarcated, subcutaneous masses with various levels of calcification
    • Inflammatory cell infiltration into fat may result in peritumoral fat stranding on fat suppressed, T2 weighted images (Radiol Med 2019;124:1049)
Radiology images

Contributed by Nasir Ud Din, M.B.B.S.

Plain Xray of leg

Images hosted on other servers:

Well defined, heterogeneous, hyperechoic nodule

Axial and coronal CT scans of cheek

Prognostic factors
  • Rare tumor recurrence of ~1 - 2% is reported with incomplete primary excision (Arch Craniofac Surg 2020;21:288, Am J Dermatopathol 2018;40:631)
  • In rare cases, can undergo malignant transformation
  • Most of the reported cases of malignant transformation have occurred in adults, typically in their 40s or 50s
    • However, there have been rare cases reported in children as well
  • Risk of malignant transformation appears to be higher in large or longstanding pilomatricoma and in those that have been previously treated with radiation therapy (J Dermatol 2010;37:735)
Case reports
  • Surgical excision is curative
Clinical images

Contributed by Mark R. Wick, M.D.

Breast skin

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Bullous pilomatricoma

Giant pilomatricoma

Preoperative appearance of face pilomatricoma

Calcified pilomatricoma

Gross description
  • Hard calcified, may be nodulocystic
  • Circumscribed edges, lobulated
  • Keratinous material appears cheesy while calcified areas are gritty
  • Rare ossified area will be difficult to cut
Gross images

Contributed by Mark R. Wick, M.D.

Breast skin

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Well circumscribed,
lobulated mass
with cheesy material

Microscopic (histologic) description
  • Lobulated and circumscribed dermal based neoplasm
  • Islands of basaloid cells exhibiting abrupt keratinization, without intervening granular layer (trichilemmal keratinization)
  • Ghost / shadow cells, may predominate
  • Basaloid cells show mitotic activity; however, abnormal mitoses are absent
  • Intermediary cells progressively more eosinophilic cytoplasm, with pyknotic nucleus
  • Tumor keratin may elicit inflammatory response with foreign body giant cells, granuloma, cholesterol clefts and calcification
  • Uncommonly metaplastic bone formation is present along with extramedullary hematopoiesis (Cureus 2022;14:e30661)
  • Hemosiderin, melanin and amyloid deposition has been reported
  • Occasionally tumors exhibit some atypical features that suggest a potential for malignancy but does not fully meet the criteria for pilomatrix carcinoma; these features include a focal infiltrative pattern at the periphery, variable cytological atypia, increased mitotic rate (up to 5/high power field) and irregular foci of central necrosis (Case Rep Dermatol 2021;13:98)
  • Histological patterns: pigmented, proliferating, nodulocystic, perforating, bullous, pilomatricoma with osseous metaplasia, melanocytic matricoma (JAAD Case Rep 2023;33:51)
Microscopic (histologic) images

Contributed by Nasir Ud Din, M.B.B.S. and Andrey Bychkov, M.D., Ph.D.

Dermal based pilomatricoma

Basaloid and shadow cells

Trichilemmal keratinization

Foreign body giant cell reaction

Shadow cells

Pilomatricoma with ossification

Ossified pilomatricoma

Dermal nodule

Basaloid nests

Ghost cells

Basal cells, giant cells and ghost cells

Virtual slides

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Circumscribed islands of ghost and basaloid cells

Circumscribed islands of ghost and basaloid cells

Cytology description
  • Clusters of basaloid cells with round to ovoid nuclei, nucleated squamous cells and anucleated squames as well as clusters of shadow cells are consistent with the characteristics typically seen in pilomatricoma (Diagn Pathol 2018;13:65)
  • Foreign body giant cells may be present; markedly calcified lesion may yield scanty material (Int J Trichology 2012;4:280)
  • Shadow cells are specialized cells, the result of a process called shadow cell degeneration, in which the cells lose their nuclei and undergo a series of structural changes
  • Cytoplasm of shadow cells often contains basophilic (blue) granules, which are thought to represent remnants of the cellular organelles
Cytology images

Contributed by R. F. Chinoy, M.D. (Case #424)
Basaloid cell smear

Basaloid cell smear

Giant cell in smear

Giant cell in smear

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Basaloid epithelial cells with scant cytoplasm

Shadow cell with keratinous cytoplasm

Cluster of shadow cells

MGG, cluster of basaloid cells

MGG, abundant cytoplasm

Positive stains
Negative stains
Electron microscopy description
  • Cell differentiation and keratinization in shadow cells is similar to the process in the cortex of hair
  • Shadow cells are fully keratinized that form a mantle around nuclear remnants

Diagnostic pearls of pilomatricoma in superficial biopsy

Pilomatricoma: mini tutorial

Sample pathology report
  • Left cheek, excision biopsy:
    • Pilomatricoma (see comment)
    • Comment: There is a well circumscribed, lobulated, dermal based adnexal neoplasm comprising of many islands of basaloid cells with scattered mitoses. These cells exhibit abrupt keratinization transforming to shadow cells. Surrounding stroma has histiocytes, foreign body giant cell reaction and foci of calcification. There is no evidence of atypical mitoses, nuclear anaplasia or destructive infiltration into the surrounding tissue. Immunohistochemical stain beta catenin shows nuclear positivity in basaloid cells. Features are consistent with pilomatricoma, a benign adnexal tumor with hair matrix differentiation. The tumor is completely excised. Local recurrence is uncommon following complete excision.
Differential diagnosis
  • Basal cell carcinoma:
    • Sun exposed areas of skin
    • Most often seen in older individuals
    • May occur in children in association with basal cell nevus syndrome, xeroderma pigmentosum and organoid nevus
    • Nests of basaloid cells palisade at periphery
    • Stromal retraction and mucin
    • High mitotic activity
    • Most show connection to epidermis
    • Lacks anucleate shadow cells
    • BerEP4 positive
  • Basal cell carcinoma with matrical differentiation:
    • Typical features of basaloid cells predominate with foci of matrical differentiation
  • Pilomatrix carcinoma:
    • Older adults; case reports document occurrence in children and young adults, mostly de novo
    • Rare cases arise from existing pilomatricoma
    • Pleomorphic basaloid cells
    • Prominent nucleoli
    • High mitotic activity, necrosis, lymphovascular invasion (rare)
    • Locally aggressive behavior, infiltrating borders
    • Local recurrence common
    • Metastases may rarely occur, involving regional lymph nodes and lungs
  • Squamous cell carcinoma:
    • Intercellular bridges
    • Epidermoid keratinization
    • Keratin pearl formation
    • Lacks shadow cells
  • Merkel cell carcinoma:
    • Small cells hyper chromatic nuclei; stippled (salt and pepper) nuclear chromatin pattern
    • Lacks anucleate shadow cells
    • Immunoreactive for neuroendocrine markers, such as chromogranin, synaptophysin, CD56 and CD57
    • Dot positivity for CK20
  • Epidermal cysts of Gardner syndrome:
    • Changes of pilomatricoma can occur
  • Other follicular tumors showing matrical differentiation, including
    • Trichoblastoma:
      • Circumscribed, dermal basaloid tumor without surface connection
      • Stromal induction and formation of primitive hair bulbs
    • Trichoepithelioma:
      • Dermal based, focal epidermal connection, branching nests of basaloid cells
      • Aggregations of fibroblasts as abortive attempts to form papillary mesenchyme (papillary mesenchymal bodies)
      • Small keratinous cysts
    • Panfolliculoma:
      • Rare, advanced follicular differentiation
      • Overlap features between trichoblastoma and matricoma
      • All elements of follicular differentiation
  • Ghost cells may also be found in noncutaneous tumors, such as calcifying cystic odontogenic tumor (CCOT), dentinogenic ghost cell tumor, odontogenic ghost cell carcinoma and craniopharyngioma; occasionally, these cells are also seen in odontomas, ameloblastoma, adenomatoid odontogenic tumor and ameloblastic fibroma (J Pharm Bioallied Sci 2015;7:S142)
Board review style question #1
A 5 year old girl presented with a hard nodule on her arm. Fine needle aspiration yielded clusters of epithelial cells with scant cytoplasm, some anucleated and nucleated squamous cells. Focal calcified debris was noticed. Which immunohistochemical stain is helpful in diagnosis?

  1. Beta catenin
  2. CK5/6
  3. Ki67
  4. p40
  5. p53
Board review style answer #1
A. Beta catenin. Beta catenin is the defining molecular alteration in pilomatricoma and nuclear staining of basaloid cells is diagnostic. Answers B and D are incorrect because CK5/6 and p40 expression is also seen in squamous cell carcinoma and some basal cell carcinoma. Answer E is incorrect because p53 aberrant expression is significant for malignant behavior and does not help in the identification of pilomatixoma. Answer C is incorrect because Ki67 will show increased staining in basaloid cells and other inflammatory cells (if present in the adjacent stroma). Identification of abrupt keratinization and ghost cells is based on H&E section.

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Reference: Pilomatrixoma
Board review style question #2

A 20 year old man had multiple gradually enlarging, itchy scalp tumors for the past 2 years. On examination it was hard nodule and overlying skin was stretched, revealing multiple facets and angles resembling a tent. The excision specimen revealed features as shown in the photomicrograph above. The patient's history is significant for total colectomy a year ago with more than 100 polyps. What is the patient suffering from?

  1. Gardner syndrome
  2. Gliomatosis cerebri
  3. Myotonic dystrophy
  4. Rubinstein-Taybi syndrome
  5. Turner syndrome
Board review style answer #2
A. Gardner syndrome. The photomicrograph shows a classic picture of basaloid cells and shadow cells, consistent with pilomatricoma. Multiple lesions and past history of total colectomy with more than 100 polyps favors familial adenomatous polyposis related syndrome, specifically Gardener syndrome. Multiple pilomatricoma (6 or more) are significant for association with various syndromes, most involving myotonic dystrophy and familial adenomatous polyposis related syndromes (including Gardner syndrome). Other syndromes include Turner syndrome, Rubinstein-Taybi syndrome, Sotos syndrome (relatively scant) and Kabuki syndrome.

Answer C is incorrect because myotonic dystrophy is part of a group of autosomal dominant disorders with high penetrance that show skeletal and respiratory muscle weakness and myotonia. Other findings may be cardiac muscle abnormalities and conduction defects, cataracts, daytime somnolence and endocrine disorders.

Answer E is incorrect because in Turner syndrome, patients are female and lack part or all of the second sex chromosome. Characteristic features include short stature, premature ovarian failure and high risk for various phenotypic abnormalities (e.g., high palate, nail dysplasia, low posterior hairline, widely spaced nipples, webbed neck and low set or malrotated ears), as well as other medical problems such as cardiovascular defects, skeletal anomalies and autoimmune disorders. It is suggested that growth hormone (or its effector molecule insulin-like growth factor 1) and estrogen may promote hair follicle growth and inhibit apoptosis, as well as produce pilomatricomas.

Answer D is incorrect because Rubinstein-Taybi syndrome is a rare genetic disorder characterized by mental retardation and multiple congenital anomalies. It involves broad thumbs and toes, short stature, distinctive facial features and varying degrees of intellectual disability. Low set ears, cataracts, microcephaly and cryptorchidism may also be seen.

Answer B is incorrect because gliomatosis cerebri is a diffuse growth pattern of glioma that invade multiple lobes of the brain. By definition, more than 2 brain regions have to be affected and symptoms include epilepsy, headaches and behavioral changes.

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Reference: Pilomatrixoma
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