Congenital melanocytic naevi and pigmentary birthmarks — branching viva

Branching framework

Open with the one-sentence problem representation. This is a large congenital melanocytic naevus on the posterior axis (the thoracic spine) with multiple satellite nevi, in a well six-week-old girl. The decisive features are the size — the projected adult size falls in the large category — and the posterior-axis location with the satellites, which is the high-risk pattern for the neurocutaneous melanocytosis. State the recognition aloud — the brown, the raised and the hairy, the presence at the birth, the size, and the satellites — before you discuss the management. The examiner is listening for whether you stratify the risk before you reach for the plan. [2] [6]

Name the classification and the size-risk relationship. The CMN is classified by the projected adult size: the small under 1.5 cm, the medium 1.5 to 19.9 cm, the large 20 cm and over, the giant 50 cm and over. The melanoma risk tracks the size — near the population risk for the small and the medium, and elevated and concentrated in the childhood for the large and the giant. Be ready for the probe on the projected adult size: it is the size the lesion will reach in the adult, derived from the body-site-specific growth factor applied to the size at the presentation, and it is the correct denominator because the lesion grows with the child. [2] [1]

Branch to the pathophysiology. The CMN is caused by the postzygotic (mosaic) NRAS codon 61 mutation in the melanocyte lineage. The earlier and the more extensive the mutation, the larger the lesion, the more numerous the satellites, and the greater the chance of the leptomeningeal involvement, because the neural crest gives rise to both the skin and the central-nervous-system melanocytes. Be ready for the probe on the surgery: the prophylactic excision does not eliminate the melanoma risk, because the melanoma may arise in the residual cells, the satellites, or the central nervous system, so the observation and the surveillance, not the routine excision, are the mainstay. [6] [3]

Branch to the neurocutaneous melanocytosis and the imaging. The high-risk pattern is the large or the giant posterior-axis CMN with the multiple satellites. The symptomatic neurocutaneous melanocytosis presents with the headache, the seizure, the developmental regression, or the hydrocephalus, and it carries the poor prognosis. The MRI of the brain and the spine screens for the leptomeningeal melanocytosis, and the contemporary practice is the selective imaging of the high-risk pattern rather than the routine imaging of every large CMN, because the detection of the clinically silent lesion does not always change the management and the imaging carries the sedation burden in the infant. The decision is made with the specialist CMN service and the neurology. [6] [3]

Branch to the syndromic cafe-au-lait macule. The six or more cafe-au-lait macules over 5 mm before the puberty (over 15 mm after the puberty) meet the NIH criterion for the neurofibromatosis type 1, and the assessment proceeds to the slit-lamp examination for the Lisch nodules, the search for the freckling and the neurofibromas, and the developmental assessment. The McCune-Albright macule is larger, fewer, and has the irregular coast-of-Maine border, and it accompanies the fibrous dysplasia and the precocious puberty. The ash-leaf macule is the hypopigmented lesion of the tuberous sclerosis, not the cafe-au-lait. [10] [11]

Branch to the dermal-melanocytosis child-protection distinction and close. The slate-blue Mongolian spot over the lumbosacral area can be mistaken for the bruise, and the documentation in the medical record at the newborn examination prevents the misdiagnosis of the non-accidental injury. Close with the counselling: the family is told the melanoma risk is elevated but not certain, the surveillance is the early detection, the prophylactic excision is not the guarantee, and the psychosocial support is the integral element. The candidate who frames the answer around the recognition, the size-risk stratification, the neurocutaneous-melanocytosis screening, and the surveillance is the candidate the boards reward. [10] [3]