AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Background

A pilomatrixoma is a benign appendageal tumor with differentiation toward hair cells. It usually manifests as a solitary, asymptomatic, firm nodule. It has long been considered a rare tumor, but it may be more common than previously realized. It is more common in children, but occurrence in adults is increasingly being recognized. Recommended treatment is surgical excision. Multiple pilomatrixomas have been observed in association with myotonic dystrophy. Pilomatrix carcinoma is a rare condition.

Pathophysiology

In one study of 10 pilomatrixoma lesions, all immunostaining results were strongly positive for bcl-2. This is a proto-oncogene that helps suppress apoptosis in benign and malignant tumors; these data suggest that faulty suppression of apoptosis contributes to the pathogenesis of these tumors.

More recently, investigators have demonstrated that the proliferating cells of human pilomatrixomas show prominent staining with antibodies directed against LEF-1 (a marker for hair matrix cells). Evidence also indicates that S100 proteins can be used as biochemical markers in characterization of pilomatrixomas. These data provide biochemical support of morphological evidence that these tumors are derived from hair matrix cells. Furthermore, investigators have shown that at least 75% of persons with pilomatrixomas who have examined have mutations in the gene CTNNB1; these data directly implicate beta-catenin/LEF misregulation as the major cause of hair matrix cell tumorigenesis in humans.

Frequency

United States

Pilomatrixomas have long been considered uncommon cutaneous tumors; however, they may be more common than is realized, especially in children and young adults. In one American dermatopathology laboratory, pilomatrical neoplasms were considered the most common solid cutaneous tumors in patients aged 20 years or younger.

International

In one dermatopathology laboratory in the United Kingdom, pilomatrixomas accounted for 1 in 500 histologic specimens. Investigators found 37 cases published in Japanese dental journals between 1977 and 1994. In Turkey, 15 patients were seen in a pediatric surgery clinic from 1984-1994. In France, a retrospective study of records in one surgery clinic revealed 33 patients who had undergone surgery for pilomatrixomas between 1989 and 1997.

Mortality/Morbidity

Pilomatrixomas are not associated with mortality. Very large tumors (£18 cm) can cause considerable discomfort but are uncommon. Pilomatrix carcinomas are also uncommon, but they are locally invasive and can cause visceral metastases and death.

Race

Most reported cases have occurred in white persons. Whether this represents publication bias or a true racial predisposition is unclear.

Sex

Most studies report a slight preponderance in females. In one retrospective study of 209 cases, the female-to-male ratio was 1.5:1.

Age

Most reported cases have occurred in children. Lesions are often discovered in the first 2 years of life; however, in a recent 1998 retrospective study of 209 cases, investigators found the age of presentation showed a bimodal pattern, with the first peak being 5-15 years and the second being 50-65 years.

CLINICAL

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

History

• Patients usually present with a solitary nodule that has been slowly growing over several months or years.
• Patients are usually asymptomatic, but some report pain during episodes of inflammation or ulceration.
• Rapid growth is rare, but reports indicate one lesion reaching 35 mm in 8 months and another reaching 1 cm in 2 weeks.
• Occurrence in more than one member of the same family is rare and is usually observed in association with myotonic dystrophy.

Physical

• Approximately 50% of the lesions occur on the head and neck, especially the cheek, preauricular area, eyelids, forehead, scalp, and lateral and posterior neck.
• • Lesions can also occur on the upper and lower extremities and trunk.
  • One lesion was observed in the middle ear and another in the ovary.
• Most lesions measure 0.5-3 cm, but, rarely, giant lesions up to 15 cm are reported.
• Patients usually have a single, firm, stony, hard nodule.
• Lesions are usually the color of the normal skin, but reddish-purple lesions have been observed (probably resulting from hemorrhage).
• Stretching of the overlying skin can give the lesion a multifaceted, angulated appearance known as the "tent sign," likely due to calcification in the lesion.
• One lesion showed the "dimple sign," which is often associated with dermatofibromas.
• Unusual morphological variants include a keratoacanthomalike appearance, perforating lesions, cystic lesions, bullous appearance, and lesions that show anetodermalike changes on the surface.

Causes

Investigators in one study showed that at least 75% of the lesions studied had mutations in the gene CTNNB1; these data directly implicate beta-catenin/LEF misregulation as the major cause of hair matrix cell tumorigenesis in humans.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Other Problems to be Considered

Breast carcinoma

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Imaging Studies

• Radiography: Plain radiography often shows nonspecific calcification of the lesion.
• Ultrasonography
• • In one review of 25 pediatric patients, investigators found that ultrasonography characteristically showed an ovoid complex mass at the junction of the dermis and subcutaneous fat, with focal thinning of the overlying dermis. It consistently appeared as a target lesion, with a hypoechoic rim and an echogenic center. The hypoechoic rim corresponded to the connective tissue capsule; the irregular echogenic center corresponded to the central island of epithelial cells.
  • Ultrasonography also shows calcification.
  • For lesions overlying the parotid gland, ultrasonography helps delineate the relationship between the lesion and the parotid gland.
• Magnetic resonance imaging
• • In one 4-year-old girl with a pilomatricoma on the neck, MRI showed a tumor with well-defined margins and high-signal intensity relative to the neck musculature on T1- and T2-weighted images.
  • MRI may be diagnostic if further reports can confirm the correlation between the high-signal bands in T2-weighted images and the bands formed by basaloid cells evident upon histologic examination.
• CT scanning: In 4 of 33 patients, CT scan of the parotid region was performed and showed a well-delineated subcutaneous tumor containing microcalcifications, but the diagnosis proposed by the radiologist was adenopathy.

Other Tests

• Fine-needle aspiration has been studied as a diagnostic tool; however, misinterpretation of the lesion as carcinoma, basal cell carcinoma, and pleomorphic adenoma with squamous metaplasia has been reported. The presence of ghost cells, basaloid cells, and calcium deposits in the appropriate clinical setting permits diagnosis by aspiration.

Procedures

• Take a biopsy specimen of lesions to look for characteristic changes that establish the diagnosis and to rule out other conditions that can clinically resemble pilomatrixoma.

Histologic Findings

The lesion is usually found in the lower dermis and subcutaneous fat. It is sharply demarcated and is usually surrounded by a connective tissue capsule. Irregularly shaped islands of epithelial cells are seen; they can be recognized as either basophilic cells or shadow cells. Basophilic cells are usually arranged either on one side or along the periphery of the tumor islands. The shadow cells have a central unstained area, corresponding to the lost nucleus. As the lesion ages, the number of basophilic cells decreases. Calcium deposits are seen in 75% of lesions with von Kossa staining.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Medical Care

Medical treatment is not successful.

Surgical Care

Spontaneous regression has never been observed. The treatment of choice is surgical excision.

• Lesions are mostly poorly delineated, but encapsulated forms have been observed; these are less likely to recur because complete resection is easier.
• Incomplete resections have been followed by local recurrence; wide resection margins (1-2 cm) have been recommended to minimize the risk of recurrence.
• Secondary lesions after surgery are rare; this risk decreases progressively with age.
• In addition, Mohs micrographic surgery has been used in an effort to ensure better margin control.

FOLLOW-UP

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Further Outpatient Care

• Patients should be monitored to ensure lesions do not recur after surgical excision.

MISCELLANEOUS

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Special Concerns

• A review of the literature in 1999 showed that 25 cases were associated with myotonic dystrophy, a rare neuromuscular disorder transmitted as an atypical autosomal dominant trait with variable expression. It is characterized by the myotonic phenomenon, consisting of difficulty in relaxing a muscle after a normal contraction. Patients tended to have multiple pilomatrixomas, with up to 31 lesions. Multiple pilomatrixomas may be a marker for myotonic dystrophy.
• Investigators have also reported isolated cases in association with Rubinstein-Taybi syndrome, Turner syndrome, Goldenhar syndrome, Churg-Strauss syndrome, sternal cleft and mild coagulative defect, and sarcoidosis. Pilomatrixomalike changes have been observed in the cutaneous cysts of persons with Gardner syndrome.
• One review of the literature in 1999 revealed 55 cases of pilomatrix carcinoma. Most occurred in patients older than 40 years (mean, 46 y; range, 8-88 y). They were locally aggressive tumors that had a tendency to recur. Four patients had visceral metastases, and death has been reported.

MULTIMEDIA

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

Media file 1:  Pilomatricoma with prominent basaloid cells.
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Media type:  Photo

Media file 2:  Ghost cells (shadow cells) and basaloid cells, associated with a granulomatous reaction. Shadow cells are also seen in this high-power micrograph.
	View Full Size Image
Media type:  Photo

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Follow-up
• Miscellaneous
• Multimedia
• References

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Article Last Updated: Feb 22, 2007