Benign acquired pigmented lesions are important for three reasons. First, these lesions must be distinguished from cutaneous melanoma, which occasionally may be a diagnostic problem (Table 1) 438. Second, some benign acquired pigmented lesions are markers of increased risk for cutaneous melanoma or even precursors to cutaneous melanoma (e.g., dysplastic naevi) (Fig. 1) 1507. People with greatly increased numbers of benign acquired naevi (even non-dysplastic) are also at increased risk of melanoma developing. Third, the presence of lentigines and café-au-lait macules may indicate the presence of certain neurocutaneous syndromes, some of which have surgical implications (see Table 3 440).

Most benign acquired pigmented lesions are not difficult to distinguish from cutaneous melanoma since they lack the irregularity of border, surface, and pigment pattern found in radial growth phase melanoma (see Section 32.5 227). Lesions that may present difficulty include some dysplastic naevi, initiated seborrhoeic keratoses, and blue naevi. The last, with its melanin pigment located in the mid-dermis, may resemble the nodular form of cutaneous melanoma. Table 1 438 shows the most characteristic features of common benign pigmented lesions.

In separate studies by Swerdlow and by Holman, the presence of increased numbers of benign acquired naevi greatly increases the risk for cutaneous melanoma. Holman noted about an 11-fold increase in patients with the presence of 10 or more palpable naevi on the arms. Swerdlow reported a risk of more than 60 fold when 50 or more naevi of diameter 2 mm or more are present (see Section 32.5 227 for additional discussion of melanoma risk factors).

The dysplastic naevus (also called B-K mole, atypical naevus, FAMMM mole, Clark's naevus) was first described in patients with familial melanoma by Clark and by Lynch. In melanoma-prone families, the risk for cutaneous melanoma appears to be transmitted as a dominant trait. Dysplastic naevi (one to many) are present in about half of the family members, and in all of those who develop melanoma. Similar findings have been reported in caucasian families from Europe and Australia. There is also an increased frequency of multiple primary melanoma in these families. In some patients the melanoma clinically appears to arise in association with a dysplastic naevus, (and may also be seen in histopathological contiguity. In others the presence of the dysplastic naevus appears to serve as a marker of increased risk. The lifetime risk of melanoma in an individual with dysplastic naevi from a family with two affected members may exceed 50 per cent.

The short arm of chromosome Ip has been linked to the familial syndrome in some American families. Other studies in The Netherlands, Australia, and in Salt Lake City have excluded this genetic location in the families studied, suggesting genetic heterogeneity of the condition. Recently, chromosome 9 has been linked to this syndrome.

Table 2 439 lists the features that distinguish dysplastic naevi from ordinary benign acquired naevi. No one feature is unique. Some highly irregular dysplastic naevi may resemble cutaneous melanoma, in which case histopathological examination may be necessary to distinguish the two.

Sporadic forms of dysplastic naevi affect about 5 per cent of the caucasian population of the United States of America. Whether all these individuals have an increased risk for melanoma is not known at this time. Kraemer has estimated a 6 per cent lifetime risk in individuals who have one or more dysplastic naevi and lack a family history of either dysplastic naevi or cutaneous melanoma. In a study of 452 patients (mixed familial and sporadic) with dysplastic naevi followed for a mean of 27 months by Rigel et al., 18 melanomas were diagnosed (12 in situ, six invasive). Since this figure is so much higher than the estimated 1 per cent lifetime risk, monitoring of patients with dysplatic naevi seems warranted.

The Spitz naevus, also termed benign juvenile melanoma, described by Sophie Spitz in 1948, deserves special comment since the diagnosis and appropriate management of these lesions may be difficult. Also termed spindle and epithelioid cell naevi, from the histopathological appearance, the Spitz naevus does not only occur in children and adolescents. The typical history is the sudden appearance of a flesh-coloured to pink or red dome-shaped papule or nodule (although in dark complexioned individuals the lesion may be deeply pigmented). Mitoses and atypical appearing cells may be present, and the pathologist may be tempted to regard these as melanoma.

However since melanoma is rare in children under the age of 10 years (<1/10&sup6;/year), all lesions diagnosed as melanoma not arising in congenital naevi in this age group should be reviewed by the pathologist with the possibility of Spitz naevus in mind. A second opinion from a melanoma reference pathologist may be of value if there is any concern about diagnosis. Diagnostic biopsy should ideally be excisional and should extend to the full depth of the lesion, since the feature of maturation with depth is helpful in the evaluation. Failure to mature with depth may indicate melanoma. Any lesions that the pathologist regards as equivocal, including such adjectives as ‘atypical’ should probably be treated with complete excision to prevent local recurrence. These patients should undergo regular cutaneous examination to exclude the unlikely possibility that the lesion was actually a melanoma masquerading as a Spitz naevus. Until more definitive techniques are available to separate Spitz naevi from melanoma, both over-diagnosis and under-diagnosis are likely to occur. Local recurrence has been reported to be infrequent in incompletely removed Spitz naevi that have ‘classical’ histopathological features.

The presence of benign lentigines and café-au-lait macules are helpful in the recognition of certain neurocutaneous syndromes (Table 3) 440. Several of these syndromes may present with signs and symptoms requiring therapy for alleviation. An example would be the development of acoustic neuroma in patients with neurofibromatosis or gastrointestinal polyps in Peutz-Jegher's syndrome. Table 4 441 presents the clinical features of neurofibromatosis.

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