Nevus psiloliparus

Happle R et al. 1998

The psiloliparus nevus is a rare fatty tissue nevus that is a marker for encephalocraniocutaneous lipomatosis, a neurocutaneous syndrome with abnormalities of the eye and central nervous system.

Clinically, the psiloliparus nevus usually presents as congenital unilateral alopecia (aplasia cutis) in the frontal or frontal-parietal region, with well-defined, sometimes irregular edges, skin-like or slightly yellowish in color.

The most characteristic features are the absence (or reduction) of hair follicles and an excessive increase in mature adipose tissue1, 2. Histologically, 3 main features are defined:

Abundance of unencapsulated mature adipose tissue that can compress and thin the dermis.

Reduction or absence of mature hair follicles.

Presence of a regular number of "orphan" piloerector muscle fascicles, i.e. independent fascicles or fascicles not associated with the hair follicle, arranged in lines parallel to the epidermal surface.

Psiloliparous nevus is often a marker of encephalocraniocutaneous lipomatosis (ECCL), a disease characterized by three factors: neurological disorders (intraspinal lipomas, asymmetry of intracranial vessels, hemispheric atrophy, ventricular dilatation, etc.), ocular disorders (coristomas, colobomas, corneal or anterior chamber disorders, etc.) and skin hamartomas (psiloliparous nevus, subcutaneous frontotemporal lipomas, subcutaneous frontotemporal lipomas, etc.). ), eye disorders (coristomas, colobomas, corneal or anterior chamber disorders, etc.) and hamartomas of the skin (psiloliparus nevus, subcutaneous frontotemporal lipomas, focal dermal hypoplasia or hypoplasia). Hamartomas of the skin are usually unilateral and are located on the face and/or scalp. The most common is the psiloliparus nevus, which is a major criterion for this syndrome. There is no correlation between the severity of the neurological disorders (which determine the prognosis of these patients) and the skin lesions.

The coexistence of nevus psiloliparus and aplasia cutis congenita (ACC) in the same lesion is referred to as aplastic psiloliparous didymosis (twin spot) according to Torrello et al. (Torrelo A et al. 2005; Ambooken B et al. 2018).

1. Ambooken B et al. (2018) Pseudodidymosis: Nevus psiloliparus with aplasia cutis congenita, an initial manifestation of Haberland syndrome Int J Dermatol 57: e160-e162
2. Ardinger HH et al. (2007) Expanding the phenotype of oculoectodermal syndrome: possible relationship to encephalocraniocutaneous lipomatosis. Am J Med Genet A 143A: 2959-2962.
3. Bennett JT et al. (2016) Mosaic activating mutations in FGFR1 cause encephalocraniocutaneous lipomatosis. Am J Hum Genet 98: 579-587.
4. Boppudi S et al. (2016) Specific mosaic KRAS mutations affecting codon 146 cause oculoectodermal syndrome and encephalo-craniocutaneous lipomatosis. Clin Genet 90: 334-342.
5. Happle R et al. (1998) Nevus psiloliparus: A distinct fatty tissue nevus. Dermatology 197: 6-10
6. Happle R et al. (2004) Nevus psiloliparus: Report of two nonsyndromic cases. Eur J Dermatol 14: 314-316
7. Hunter AG (2006) Oculocerebrocutaneous and encephalocraniocutaneous lipomatosis syndromes: blind men and an elephant or separate syndromes? Am J Med Genet A 140: 709-726.
8. Llamas-Velasco M et al. (2011) Nevus psiloliparus in a child with encephalocraniocutaneous lipomatosis. Actas Dermosifiliogr 102: 303-305
9. Moog U (2009) Encephalocraniocutaneous lipomatosis. J Med Genet 46: 721-729.
10. Peacock JD et al. (2015) Oculoectodermal syndrome is a mosaic RASopathy associated with KRAS alterations. Am J Med Genet A 167: 1429-1435 Pediatr Dermatol 22: 206-209
11. Richters RJH et al (2020) Oculoectodermal Syndrome - Encephalocraniocutaneous Lipomatosis Associated with NRAS Mutation. Acta Derm Venereol. 2020 Apr 6;100(8):adv00103.
12. Sharifi M et al. (2016) Encephalocraniocutaneous lipomatosis (Fishman syndrome): A rare neurocutaneous syndrome. J Curr Ophthalmol 28: 155-158
13. Torrelo A et al. (2005) Nevus psiloliparus and aplasia cutis: A further possible example of didymosis