CLINICAL AND LABORATORY INVESTIGATIONS

Use of Ultrasonography in the Diagnosis ofChildhood Pilomatrixoma

Jenny Hughes, M.D., M.R.C.P.,* Albert Lam, M.B., B.S., F.R.A.C.R., D.D.U.,† andMaureen Rogers, M.B., B.S., F.A.C.D.‡

*Department of Dermatology, Hillingdon Hospital, Uxbridge, Middlesex, United Kingdom, and Departments of†Medical Imaging and ‡Dermatology, New Children’s Hospital, Sydney, Australia

Abstract: Pilomatrixomas are relatively common childhood tumorsthat usually occur in the head and neck region. The clinical diagnosis ofthese lesions may be difficult, especially if the examining physician isunfamiliar with them. Excision is usually recommended, as a foreign bodyreaction due to calcification of the lesion may occur and cause a vigorousinflammatory response with risk of scarring. A retrospective study wascarried out by examining the preoperative ultrasound scans of 28 sus-pected pilomatrixomas in 25 children. The findings on sonography werecorrelated with the histologic results in 19 cases (18 pilomatrixomas andone ruptured epidermoid cyst). In the majority of patients, sonographyeither correctly supported or excluded the clinical diagnosis of piloma-trixoma and contributed to appropriate preoperative assessment andsubsequent management of the lesion. We therefore found sonography ofsuspected pilomatrixomas in children to be a useful and noninvasiveprocedure, offering a significant improvement in the accurate diagnosisof these lesions.

Pilomatrixomas (formerly known as calcifying epithe-liomas of Malherbe) are benign, deep dermal or subcu-taneous tumors that are derived from the hair follicle (1).Originally described by Malherbe and Chenantais (2) asa calcifying tumor arising from the sebaceous gland, itwas reclassified as a pilomatrixoma once immunohisto-chemical and ultrastructural studies confirmed hair fol-licle origin (3).

Pilomatrixomas are slowly enlarging tumors that de-velop usually during the first two decades of life, mainlyin the head and neck areas (4). There is a female pre-dominance (5). They are commonly asymptomatic, butare occasionally tender. Most occurrences are solitarylesions, but they may be multiple and the latter have been

associated with myotonic dystrophy (6). Pilomatrixomasgenerally range in size from 0.5 to 3 cm, although giantlesions larger than 10 cm in size have been reported (7).The lesions are raised in relation to the skin surface andare characteristically hard and knobbly or multifacetedon palpation. They may be of normal skin color or white(Fig. 1) and may have a bluish tinge. Some can becomeinflamed, presenting as a granulomatous swelling, withoccasional extrusion of calcium as a thick, white, grittysubstance (Fig. 2).

Histopathology (1,8) demonstrates a well-demarcatedtumor, often with a connective tissue capsule (Fig. 3).Irregularly shaped islands of epithelial cells are embed-ded in a rather cellular stroma. Usually two types of cells

Address correspondence to Maureen Rogers, M.B., Children’s Hos-pital Medical Centre, Hainsworth St., Westmead, NSW 2145, Austra-lia.

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are seen within the islands, basophilic cells and shadowcells, but in some tumors the former are absent. Thebasophilic cells have indistinct cell borders and the nu-clei appear massed. These cells can be seen transforminginto “ghost” or shadow cells, which lack nuclei. Theyhave a distinct border and a central unstained area which

is a shadow of the lost nucleus. Calcification is com-monly encountered as fine basophilic granules within thecytoplasm of the shadow cells or as large sheets of amor-phous basophilic material (Fig. 4). Ossification is a rarefeature. The stroma of the tumor often shows a foreignbody giant cell reaction adjacent to the shadow cells.

Ultrasonography is increasingly used as an aid in thediagnosis of skin tumors (9). We studied the ultrasoundscans of all children in our unit with suspected piloma-trixoma to assess whether sonography aids in the diag-nosis and preoperative assessment of this condition.

MATERIALS AND METHODS

All children with clinically suspected pilomatrixoma pre-senting to the dermatology department of New Chil-dren’s Hospital, Sydney, Australia, within the last 4years who had ultrasound examination of these lesionswere included in the study. Patients were identified viathe clinical coding systems of the dermatology and radi-ology departments. The ages of the patients and the sitesof the lesions were documented. Ultrasonography hadbeen carried out using an ACUSON 128 xP (MountainView, CA) unit with a 7 mHz linear transducer capableof allowing color Doppler and duplex sonographic evalu-ation. A preliminary gray scale sonogram was obtainedwith sufficient coupling gel or a standoff to define theskin and subcutaneous tissue within the mass lesion. Thelesion was imaged in two perpendicular planes and thesize measured. The compressibility of the lesion wastested with gentle compression by the transducer. Thiswas followed by color Doppler and duplex studies. His-topathologic analysis was performed on 19 lesions in 16patients.

RESULTS

The results are summarized in Table 1, with the patientssorted according to ultrasound findings for easier ap-

Figure 1. Pilomatrixoma presenting as a white raised tu-mor on a cheek (arrow).

Figure 2. Pilomatrixoma demonstrates foreign body reac-tion with inflammation and extrusion of calcium.

Figure 3. Scanning view of section of pilomatrixomashows connective tissue capsule and islands of epithelialcells.

Figure 4. Section of pilomatrixoma demonstrates calcifi-cation (arrow) appearing as a sheet of basophilic material.

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praisal. Of 25 patients with 28 clinically suspected pi-lomatrixomas, ultrasound examination supported theclinical diagnosis in 20 instances. In 16 of these 20 cases,histopathology confirmed the diagnosis of piloma-trixoma. In one instance histopathology showed the le-sion to be a ruptured epidermoid cyst, and in another thelesion resolved prior to surgery, indicating that the clini-cal and ultrasound diagnoses were incorrect. In one pa-tient surgery has been postponed and one patient was lostto follow-up.

Ultrasound examination failed to support the clinicaldiagnosis in eight cases. In two cases histopathologyshowed the lesions to be pilomatrixomas; these had beenidentified on ultrasound examination as calcified epider-moid cysts. In five cases the ultrasound findings led to adecision not to proceed with surgery, and all of theselesions resolved spontaneously; the ultrasound diagnoseswere no identifiable lesion (one case), nonspecific softtissue thickening (three cases), and discharged cyst (onecase). In the final case, the ultrasound diagnosis wasepidermoid cyst and surgery has been postponed.

DISCUSSION

In most of the studies involving the use of ultrasound inskin tumors, the modality has not been used as a formaldiagnostic test (10,11). One recent article describes theuse of sonography (7.5 mHz linear array probe) in two

patients with preauricular tumors where the diagnosiswas uncertain (12). Both lesions were pilomatrixomasand had the characteristic ultrasound findings of a well-defined subcutaneous mass with a dense acoustic shadowsuggestive of calcification.

Our findings were similar, allowing a diagnosis ofpilomatrixoma to be confirmed preoperatively in manycases and correctly excluding it in others. The extent ofthe lesion was delineated, guiding the surgeon, especiallywith larger lesions.

In our study of 28 clinically suspected pilomatrixomasin 25 patients, ultrasound supported the diagnosis in 20of 28 cases. That the ultrasound diagnosis was correctwas confirmed by microscopic examination in 16 of 20cases (80%). The diagnosis was incorrect in 2 of 20 cases(10%), one shown on histopathology to be a rupturedepidermoid cyst and the other resolving prior to surgery.In 2 of 20 cases (10%), information on outcome is un-available.

Ultrasound suggested alternative diagnoses in 8 of the28 tumors. The exclusion of pilomatrixoma was almostcertainly correct in 5 of 8 cases (62.5%) in which thelesions resolved. In 2 of 8 cases (25%) the exclusion wasincorrect, as histopathology demonstrated pilomatrixoma.In one case, information on outcome is unavailable.

In one study of 51 cases of histologically proved pi-lomatrixoma (13) the initial referring diagnosis was in-

TABLE 1. Summary of Clinical Features, Ultrasound Diagnoses, and Outcomes in 28 Cases of Clinically SuspectedPilomatrixoma in 25 Patients

Case Age Sex Site Ultrasound Diagnosis Outcome

1 4 years Female Cheek Pilomatrixoma Histopathology pilomatrixoma2 3 years Female Cheek Pilomatrixoma Histopathology pilomatrixoma3 2 years Female Cheek Pilomatrixoma Histopathology pilomatrixoma4 3 years Female Preauricular Pilomatrixoma Histopathology pilomatrixoma5 3 years Male Cheek Pilomatrixoma Histopathology pilomatrixoma6 1 year Male Temple Pilomatrixoma Histopathology pilomatrixoma7 1 year Female Preauricular Pilomatrixoma Histopathology pilomatrixoma8 8 years Male Preauricular Pilomatrixoma Histopathology pilomatrixoma9 8 months Male Temple Pilomatrixoma Histopathology pilomatrixoma

10 15 months Female Cheek Pilomatrixoma Histopathology pilomatrixoma11 8 years Male Scapula Pilomatrixoma Histopathology pilomatrixoma12 14 years Female Arm Pilomatrixoma Histopathology pilomatrixoma13 14 years Female Arm Pilomatrixoma Histopathology pilomatrixoma14 14 years Female Eyebrow Pilomatrixoma Histopathology pilomatrixoma15 1 year Female Eyebrow Pilomatrixoma Histopathology pilomatrixoma16 1 year Female Eyebrow Pilomatrixoma Histopathology pilomatrixoma17 2 years Female Cheek Pilomatrixoma Histopathology epidermoid cyst18 3 years Female Cheek Pilomatrixoma Resolved19 5 years Male Shoulder Pilomatrixoma Surgery postponed20 7 months Female Cheek Pilomatrixoma Lost to follow-up21 4 months Female Chin Calcified epidermoid cyst Histopathology pilomatrixoma22 5 years Female Eyelid Calcified epidermoid cyst Histopathology pilomatrixoma23 3 years Female Cheek No identifiable lesion Resolved24 3 years Male Cheek Nonspecific soft tissue thickening Resolved25 7 months Male Cheek Nonspecific soft tissue thickening Resolved26 2 years Female Cheek Nonspecific soft tissue thickening Resolved27 5 years Female Nose Discharged cyst Resolved28 1 year Male Cheek Epidermoid cyst Surgery postponed

Hughes et al: Ultrasonography in the Diagnosis of Childhood Pilomatrixoma343

correct in 94% of cases and the preoperative diagnosiswas incorrect in 57% of cases, suggesting that ultraso-nography may have significantly improved diagnosticaccuracy, limiting unnecessary investigations and surgery.

The characteristic sonographic appearance of a pi-lomatrixoma is an ovoid complex mass found at the junc-tion of the dermis and the subcutaneous fat with focalthinning of the overlying dermis. It consistently presentsas a “target” lesion with a hypoechoic rim and an echo-genic center (Figs. 5–6). The hypoechoic rim corre-sponds to the connective tissue capsule and the irregularechogenic center corresponds to the central islands ofepithelial cells (Fig. 3). The calcification (Fig. 4) ac-counts for the posterior shadowing of the nidus (Fig. 6).

Sonography of subcutaneous lesions is already a use-ful technique, but with 15 MHz probes, better imageswill be available, further improving the differentiationand diagnosis of skin tumors. However, sonography ofcertain regions (e.g., close to the eye) will always beharder to interpret, as a tangential position is necessary togive good resolution.

Computerized tomography (CT) and magnetic reso-nance imaging (MRI) cannot be performed in childrenwithout sedation or general anesthesia, and they are rela-tively invasive and expensive ways of assessing childrenwith clinically suspected pilomatrixomas or other skintumors. Also the definition of the lesion is limited by itssmall size. Radiographs are only useful in the diagnosisof suspected pilomatrixoma when there is significant cal-cification (14).

In conclusion, we have found sonography to be anoninvasive, quick, inexpensive, and reasonably reliablemeans of imaging suspected pilomatrixomas and an aidto planning further management.

REFERENCES

1. Solanki P, Ramzy I, Durr N, Henkes D. Pilomatrixoma:cytologic features with differential diagnostic consider-ations. Arch Pathol Lab Med 1987;111:294–297.

2. Malherbe A, Chenantais J. Note sur l’epitheliome calcifiedes glandes sebacees. Prog Med 1880;8:826–828.

3. Forbis R Jr, Helwig EB. Pilomatrixoma (calcifying epithe-lioma). Arch Dermatol 1961;83:606–618.

4. Jacobsen AS, Bowen J, Bruce J, Gough DCS. The calci-fying epithelioma of Malherbe in children: a 15 year ex-perience. Pediatr Surg Int 1995;10:44–45.

5. Macleod AJ, Scobie WG. Pilomatrixoma as a diagnosticproblem: the Edinburgh experience. J R Col Surg Edinb1991;36:261–263.

6. Chiaramonti A, Gilgor RS. Pilomatricomas associated withmyotonic dystrophy. Arch Dermatol 1978;114:1363–1365.

7. Rothman D, Kendall AB, Baldi A. Giant pilomatrixoma.Arch Surg 1976;111:86.

8. Elder D, Elenitsas R, Ragsdale BD. Tumors of the epider-mal appendages. In: Elder D, eds. Lever’s histopathologyof the skin, 8th ed. Philadelphia: Lippincott-Raven, 1997.

9. Stiller MJ, Gropper CA, Shupack JL, Lizzi F, Driller J,Rorke M. Diagnostic ultrasound in dermatology: currentuses and future potential. Cutis 1994;53:44–48.

10. Fornage BD, McGavran MH, Duvic M, Waldron CA. Im-aging of the skin with 20-MHz US. Radiology 1993;189:69–76.

11. Harland CC, Bamber JC, Gusterson BA, Mortimer PS.High frequency, high resolution B-scan ultrasound in theassessment of skin tumours. Br J Dermatol 1993;128:525–532.

12. Fink AM, Berkowitz RG. Sonography in pre-auricular pi-lomatrixoma of childhood. Ann Otol Rhinol Laryngol1997;106:167–169.

13. Wells NJ, Blair GK, Magee JF, Whiteman DM. Piloma-trixoma: a common, benign childhood skin tumour. Can JSurg 1994;37:483–486.

14. Haller JO, Kassner EG, Ostrowitz A, Kottmeier PK,Pertschuk LP. Pilomatrixoma (calcifying epithelioma ofMalherbe): radiographic features. Radiology 1977;123:151–153.

Figure 5. Ultrasound appearance of pilomatrixoma. A lon-gitudinal section of the lesion shows an ovoid “target” le-sion (arrow) at the junction of the dermis and subcutane-ous fat. A thin, irregularly hypoechoic rim surrounds anechogenic center.

Figure 6. Typical ultrasound appearance shows an echo-genic center surrounded by a thin hypoechoic rim. Thereis posterior shadowing (arrow) from the echogenic centerindicating the presence of calcification.

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