The lesion is usually characterized by a sharply-demarcated, wedge-shaped lesion with its base in parallel with the epidermis and its apex oriented toward the subcutaneous fat or deep reticular dermis. Case images

There may be asymmetry, plump but fairly regular nests of melanocytes in the dermis.

Cytologic atypia with some nuclear pleomorphism and a small to medium-sized eosinophilic nucleolus is present.

There is absence of maturation of cells.

Mitotic activity is low. No atypical mitotic figures are present. There may be occasional presence of normal dermal mitoses.

Patchy mononuclear inflammatory cellular infiltrate is evident.

Although unusual, such histologic features should not be regarded as a sign of malignancy in deep penetrating nevi.

The cells surround hair follicle, sweat glands and nerves.

Pilar muscles are some times infitrated.

Many authors regard this lesion as a variant of blue naevus.

The relevant differential diagnosis include melanoma :

1.Melanoma of the thickness of deep penetrating naevus usually displays marked cellular and architectural atypia.

2. In deep penetrating naevus there is no pagetoid intraepidermal spread.

3. There is no irregular epidermal acanthosis or thinning

4. No irregular fibroinflammatory dermal response is seen in deep penetrating naevus.

5. Proliferating cell nuclear antigen (PCNA) is present in scattered melanocytes (less than 5%) in the deep penetrating nevus. In melanoma 25%-75% cells show immunopositivity with PCNA.

Case Links: Case1 ; Case 2

Abstracts:

Deep penetrating nevus: a distinct variant of melanocytic nevus.Indian J Pathol Microbiol. 2011 Jan-Mar;54(1):156-7.

Deep penetrating nevus: a case report and brief literature review.Diagn Pathol.2006 Sep 25;1:31

Linear arrangement of multiple deep penetrating nevi: report of first case and review of literature.Arch Dermatol.2003 Dec;139(12):1608-10

Pitfalls in the diagnosis of malignant melanoma . Magy Onkol. 2003; 47:27-39. Epub 2003 Apr.

Current diagnostic problems in melanoma pathology. Semin Cutan Med Surg.2003 ;22(1):33-41

Pathology and prognostic factors.Curr Opin Oncol.1993;5(2);364-7

Deep penetrating (plexiform spindle cell) nevus. A frequent participant in combined nevus.J Cutan Pathol. 1992;19(3):172-80.

Deep penetrating nevus.Am J Surg Pathol. 1989 Jan;13(1):39-44.

Deep penetrating nevus.Arch Dermatol. 1993 Mar;129(3):328-31.
BACKGROUND--Deep penetrating nevus is a variant of melanocytic nevi with histologic features that may be alarming and can be mistaken for malignant melanoma. We are presenting a review of the clinical findings and the histologic features of deep penetrating nevus in a series of 14 cases. OBSERVATIONS--Deep penetrating nevus occurs most commonly over the acral skin of young adults. Clinically, the lesions were diagnosed as pigmented nevus, blue nevus, or malignant melanoma. Histologically, deep penetrating nevus shows a wedge-shaped lesion extending to the deep dermis and the subcutaneous fat tissue. Nests and fascicles of pigmented melanocytes extended deep at the periphery of blood vessels, nerves, and the cutaneous adnexa. Low-grade cellular atypia is present and mitoses are rare. CONCLUSIONS--Deep penetrating nevus is a variant of benign pigmented nevi with deep dermal and subcutaneous involvement. The pattern should be recognized and differentiated from malignant melanoma.