Although it is often difficult to make a diagnosis based on clinical grounds alone, and most if not all lumps that do not resolve spontaneously over time will eventually be excised, it is helpful to limit the wide range of possible diagnoses using clinical criteria. Criteria that may serve this purpose are:

Table 92.2 Differential diagnosis of cutaneous lumps by colour

Table 92.3 Differential diagnosis of cutaneous lumps by surface appearance

Table 92.4 Differential diagnosis of cutaneous lumps by texture

In addition to these criteria, tenderness (Table 92.5) and itchiness (Table 92.6) are important features that are associated with certain lesions.

Table 92.5 Skin lumps that may be tender/painful

Table 92.6 Skin lumps that are itchy

References

1 Knight PJ, Reiner CB. Superficial lumps in children: what, when, and why? Pediatrics 1983;72:147–53.

2 Schmoeckel C. Lexikon und Differential Diagnose der Klinischen Dermatologie. Stuttgart: Thieme, 1994.

3 Harper JI. Handbook of Paediatric Dermatology, 2nd edn. London: Butterworth, 1990:127–31.

Individual Skin Tumours

The many different individual skin nodules and cysts are described in the relevant chapters. The following are covered in detail in this chapter.

Pilomatricoma (Also Pilomatrixoma)

Definition.

Pilomatricoma, also known as trichomatricoma and previously referred to as calcifying epithelioma of Malherbe, is a benign tumour of hair matrix cells. It is considered to be a hamartoma. Pilomatricomas account for 10% of all types of skin nodules and/or cysts in childhood [1].

Pathogenesis.

The tumour is derived from immature hair matrix cells. It shows evidence of keratinization and frequently (75%) undergoes calcification. Histopathology reveals a sharply demarcated, frequently encapsulated tumour in the lower dermis, embedded in islands of epithelial cells. Among these, basophilic and shadow cells can be recognized [2]. Chan et al. [3] identified activating mutations of beta-catenin in a high percentage of pilomatricomas.

Clinical Features.

Pilomatricomas are firm, solitary, asymptomatic papules or nodules in the dermis or subcutaneous tissue covered by normal skin (Fig. 92.1). If more superficially located, they can appear with a blue–red discoloration. The nodules typically measure 0.5–3.0 cm in diameter. They are mainly located on the head and neck (50–55%), on the upper extremities (25–30%) and, rarely (15–25%), on the trunk and legs. Most cases (60%) occur in childhood and adolescence, and two-thirds of these occur before the age of 10 years. There is a 2 : 1 female preponderance [1,4]. Multiple and familial cases are rare [5]. The presence of multiple pilomatricomas have been reported in association with Gardner syndrome [5], myotonic dystrophy [6], Turner syndrome [7], Rubinstein–Taybi syndrome [8], familial Sotos syndrome [9] and MYH-positive familial adenomatous polyposis [10]. Possible associations also have been reported in sarcoidosis, HIV and trisomy 9 [11,12].

Fig. 92.1 Pilomatricoma.

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