BASICS
DESCRIPTION
- Benign, adnexal skin tumor derived from hair matrix cells
- Slow-growing, hard, typically solitary nodule found in the dermis/subcutaneous layer of the skin
- Most commonly occurs on the head and neck of children and young adults (1)
- Variants:
- Pilomatrix carcinoma, a rare malignant variant, can be locally invasive and have a high recurrence rate. Infrequent cases of metastases have been reported.
- Perforating pilomatricoma
- Synonym(s): pilomatrixoma; calcifying epithelioma of Malherbe; trichomatricoma
- System(s) affected: integumentary
EPIDEMIOLOGY
Incidence
- Pilomatricoma was first described in 1880 by Malherbe and Chenantais (2).
- Incidence of pilomatricomas has not been well studied.
- One study reported an incidence of 1.04% of all benign skin tumors examined and 0.08% of all histologic samples reviewed.
- Slight female preponderance (male-to-female ratio, 1:1.1).
- Most frequently occurs in patients <20 years old (37 " 46%), with some reports of a second smaller peak in the 5th to 7th decades of life.
- Pilomatrix carcinoma is more common in males and the elderly but is extremely rare, with <80 total cases reported.
ETIOLOGY AND PATHOPHYSIOLOGY
- Pilomatricomas derive from the primitive basaloid cells of the epidermis that differentiate into hair matrix cells with uncontrolled proliferation in the dermis/subcutaneous tissue.
- There are anecdotal reports of lesions arising in areas of trauma, insect bites, and surgery (3.9% of cases).
Genetics
- Activating ²-catenin gene (CTNNB1) mutations are thought to play an important role.
- A high level of ²-catenin results in the stimulation of cellular proliferation and/or inhibition of cell death. (3).
RISK FACTORS
No known risk factors
COMMONLY ASSOCIATED CONDITIONS
Although uncommon, multiple pilomatricomas have been associated with the following conditions:
- Myotonic dystrophy
- Turner syndrome
- Rubinstein-Taybi syndrome
- Trisomy 19
- Sotos syndrome
- Gardner syndrome
DIAGNOSIS
HISTORY
- Usually asymptomatic
- Some patients may complain of mild tenderness or pain secondary to palpation, pruritus, or inflammation.
PHYSICAL EXAM
- Most frequently located on the head and neck (54 " 73%) but may also appear on an upper limbs (23 " 26%), lower limbs (14%), or trunk
- Typically presents as a solitary, well-circumscribed, mobile, firm dermal or subcutaneous nodule
- Skin overlaying the lesion usually has a normal appearance but may have a pink or bluish hue or may become semitransparent, atrophic, or ulcerate.
- Ranges in size from 1 to 50 mm, although most commonly ≤15 mm.
- The "tent sign " is assessed for by stretching the overlaying skin taut, revealing the irregular contours of the nodule.
- The "teeter-totter sign " is elicited by pressing on one edge of the lesion which causes the opposite edge to protrude from the skin (2).
- The "skin crease sign " is elicited by squeezing the edge of the nodule with both thumbnails, perpendicular with the skin tension line, which appears to be helpful with preoperative diagnosis (4).
- Calcium may be visible through the surface as yellow or white flecks.
DIFFERENTIAL DIAGNOSIS
- Sebaceous cyst
- Epidermoid cyst
- Dermoid cyst
- Neurofibroma
- Foreign body reaction
- Calcified hematoma
- Calcified lymph node
- Vascular lesion
- Basal cell carcinoma
- Squamous cell carcinoma
- Fat necrosis
- Nonspecific cyst
DIAGNOSTIC TESTS & INTERPRETATION
- The diagnosis of pilomatricoma is predominately made clinically and confirmed by pathology.
- The correct preoperative diagnosis of pilomatricoma by physicians is relatively low (28 " 46%).
Initial Tests (lab, imaging)
- Use of radiography, CT, ultrasound, and MRI to aid with diagnosis has been reported, but they are not used routinely.
- Ultrasound may be used as a noninvasive option that may show a well-defined mass with inner echogenic foci and a peripheral hypoechoic rim or a completely echogenic mass with strong posterior acoustic shadowing in the subcutaneous layer (5).
Diagnostic Procedures/Other
- Punch biopsy
- Fine-needle aspiration cytology has been described as a relevant preoperative diagnostic procedure for masses in the head and neck; however, care must be taken to avoid misdiagnosing pilomatricoma as a malignant lesion (6).
- Pilomatricomas have been shown to appear as a dark mass using otoscope transillumination, which may aid in preoperative diagnosis.
Test Interpretation
- Histologically, pilomatricomas are well-circumscribed and encapsulated masses filled with palisading basaloid cells and islands of eosinophilic "shadow " or "ghost " cells and are frequently associated with a foreign body giant cell reaction and dystrophic calcification.
- Bony metaplasia, hemosiderin, and melanin deposition may also be present.
- Pilomatrix carcinoma is indicated by the presence of pleomorphic cells, increased atypia and mitotic figures, central necrosis, and local infiltration of blood vessels and soft tissue.
TREATMENT
- Treatment of choice is simple excision with minimal margins.
- Pilomatricomas do not spontaneously regress; however, perforating pilomatricomas may extrude spontaneously.
- Skin grafts may be necessary to cover the area of resection, depending on the volume removed and the degree of adherence to the epidermis.
ONGOING CARE
COMPLICATIONS
Recurrence is rare (0.48 " 6%) and usually due to incomplete excision.
REFERENCES
11 Hills SE, Maddalozzo J. Congenital lesions of epithelial origin. Otolaryngol Clin North Am. 2015;48(1):209 " 223.22 Pant I, Joshi SC, Kaur G, et al. Pilomatricoma as a diagnostic pitfall in clinical practice: report of two cases and review of literature. Indian J Dermatol. 2010;55(4): 390 " 392.33 Hassanein AM, Glanz SM, Kessler HP, et al. Beta-catenin is expressed aberrantly in tumors expressing shadow cells. Pilomatricoma, craniopharyngioma, and calcifying odontogenic cyst. Am J Clin Pathol. 2003;120(5):732 " 736.44 Kim IH, Lee SG. The skin crease sign: a diagnostic sign of pilomatricoma. J Am Acad Dermatol. 2012;67(5):e197 " e198.55 Hwang JY, Lee SW, Lee SM. The common ultrasonographic features of pilomatricoma. J Ultrasound Med. 2005;24(10):1397 " 1402.66 Ieni A, Todaro P, Bonanno AM, et al. Limits of fine-needle aspiration cytology in diagnosing pilomatrixoma: a series of 25 cases with clinico-pathologic correlations. Indian J Dermatol. 2012;57(2):152 " 155.
ADDITIONAL READING
- Barreto-Chang OL, Gorell ES, Yamaguma MA, et al. Diagnosis of pilomatricoma using an otoscope. Pediatr Dermatol. 2010;27(5):554 " 557.
- Guinot-Moya R, Valmaseda-Castellon E, Berini-Aytes L, et al. Pilomatrixoma. Review of 205 cases. Med Oral Patol Oral Cir Bucal. 2011;16(4):e552 " e555.
- Hassanein AM, Glanz SM. Beta-catenin expression in benign and malignant pilomatrix neoplasms. Br J Dermatol. 2004;150(3):511 " 516.
- Kumaran N, Azmy A, Carachi R, et al. Pilomatrixoma " accuracy of clinical diagnosis. J Pediatr Surg. 2006;41(10):1755 " 1758.
- Marrogi AJ, Wick MR, Dehner LP. Pilomatrical neoplasms in children and young adults. Am J Dermatopathol. 1992;14(2):87 " 94.
- O 'Connor N, Patel M, Umar T, et al. Head and neck pilomatricoma: an analysis of 201 cases. Br J Oral Maxillofac Surg. 2011;49(5):354 " 358.
- Ohnishi T, Nakamura Y, Watanabe S. Perforating pilomatricoma in a process of total elimination. J Am Acad Dermatol. 2003;49(2)(Suppl Case Reports):S146 " S147.
- Price HN, Zaenglein AL. Diagnosis and management of benign lumps and bumps in childhood. Curr Opin Pediatr. 2007;19(4):420 " 424.
- Tselis N, Heyd R, Vogt HG, et al. Pilomatrix carcinoma with lymph node and pulmonary metastases. Strahlenther Onkol. 2006;182(12):727 " 732.
CODES
ICD10
- D23.9 Other benign neoplasm of skin, unspecified
- D23.30 Other benign neoplasm of skin of unspecified part of face
- D23.4 Other benign neoplasm of skin of scalp and neck
- D23.39 Other benign neoplasm of skin of other parts of face
ICD9
- 216.9 Benign neoplasm of skin, site unspecified
- 216.3 Benign neoplasm of skin of other and unspecified parts of face
- 216.4 Benign neoplasm of scalp and skin of neck
SNOMED
Pilomatrixoma
CLINICAL PEARLS
- Pilomatricoma is a benign, relatively infrequent, slow-growing, adnexal skin tumor.
- Most frequently reported in children and young adults
- Typically appears as a solitary, firm, asymptomatic nodule beneath the skin
- The "tent sign " and "teeter-totter sign " are helpful clinical clues.
- Diagnosis is made by histology. Imaging is limited.
- Treatment of choice is simple excision.