Congenital Basaloid Linear Nevus in a Six-Month-Old Child

This image is a composite of gross and microscopic photographs taken of a skin lesion resected from the scalp of a 6-month-old child. What is your diagnosis?

Answer:

Congenital basaloid linear nevus.

Comments:

Congenital basaloid linear nevus represents a developmental malformation that involves the epidermis. It clinically manifests as discrete linear patches or plaques along the Blaschko lines.[1] Lesions may exhibit diverse clinical appearances, which can be attributed to its variable histological patterns. Nearly all lesions occur on the neck, trunk, and extremities. Rare sites of presentation include intraoral and face.[1]

Grossly, typical lesions appear as multiple warty brown patches or plaques that may form a linear or zosteriform lesion or can be more verrucous and hyperpigmented.[1] [2] [3] It may also show wrinkled skin appearance as in our case. Grossly, the resected specimen was an ellipse of skin, 2.0 × 1.7 × 0.3 cm. The skin surface was covered by wrinkled cerebriform raised of flat nodules, the largest 1.8 cm.

It may be present at birth or appears in infancy. Histologically, lesions are characterized by epidermal papillomatosis and acanthosis with no associated adnexal structures.[1] [2] [Fig. 1] shows the grossly wrinkled appearance with histology depicting papillomatosis and acanthosis. Histologically, they can have several different patterns: keratinocytic, seborrheic keratosis like, verrucoid, acrokeratosis verruciformis, and porokeratotic, among others. Microscopic examination usually reveals a hamartomatous proliferation consisting of epidermal papillomatosis and acanthosis with no associated adnexal structural abnormalities. [Fig. 1] shows the gross appearance of the excised lesion with abundant wrinkles and the microscopic features including epidermal papillomatosis and acanthosis with no other significant changes.

Fig. 1 Figure showing gross and microscopic findings of the warty lesion with wrinkled appearance and papillomatosis.

Differential diagnoses include nevus sebaceus of Jadassohn, seborrheic keratosis, verruca vulgaris, and acanthosis nigricans.[3] Nevus sebaceus presents as a single yellow/orange patch on the scalp and shows histologically similar epidermal changes, though with additional sebaceous gland alterations, primitive hair follicles, and ectopic dilated apocrine glands. Sebaceous keratosis has pseudohorn cysts, squamous eddies, and compact basaloid cells. Verruca vulgaris has papillomatosis, hypergranulosis, hyperparakeratosis, and koilocytic changes. The verrucoid pattern of congenital basaloid linear nevus can show hyperkeratosis (orthokeratosis and parakeratosis), vacuolated cells in the granular and upper spinous layer, and increased keratohyaline granules without prominent vascularity in the papillary dermis (typical of verruca vulgaris). Acanthosis nigricans is usually found in flexural areas of the body, particularly the axilla, and is associated with an underlying metabolic disorder or malignancy and shows lesser degrees of hyperkeratosis and papillomatosis.[3] Acanthosis nigricans-like pattern of congenital basaloid linear nevus shows hyperkeratosis, papillomatosis, and mild irregular acanthosis with poorly developed rete ridges. Congenital basaloid linear nevus can be a component of a syndromic constellation, notably Proteus syndrome (overgrowth of skin and connective tissue), type II segmental Cowden disease (neural defects, overgrowth of limbs and toes, polyps, and nevi), and fibroblast growth factor receptor 3 epidermal nevus syndrome (keratinocytic epidermal nevus, acanthosis nigricans, and neurological abnormalities), among others.[1] [3] Basal cell nevus syndrome is an autosomal dominant inherited disease caused by PTCH1 (9q22.3-q31) germline mutations and must be kept in mind as a differential.[4] Management of congenital basaloid linear nevus is usually by surgical resection.[1] [2]

No conflict of interest has been declared by the author(s).

Authors' Contributions

S.B.K. made the diagnosis, edited the manuscript, and prepared composite photo. S.S. wrote the first draft and performed literature search.

Conflict of Interest

None declared.

• References

• 1 Calonje JE, Brenn T, Lazar AJ, Billings SD. McKee’s Pathology of the Skin. 5th ed.. Elsevier; 2019
• 2 Taylor RS, Perone JB, Kaddu S, Kerl H. Appendage tumors and hamartomas of the skin. Fitzpatrick's dermatology. Gen Med (Saga) 2008; 1: 1086-1087
• 3 Knittel R, Ardakani NM. Epidermal nevus. PathologyOutlines.com website. Accessed April 22nd, 2025 at: https://www.pathologyoutlines.com/topic/skintumornonmelanocyticepidermalnevus.html
• 4 Besagni F, Dika E, Ricci C. et al. Basaloid follicular hamartomas in pediatric basal cell nevus syndrome: a diagnostic challenge. J Dermatol 2021; 48 (07) 1101-1105

Publication History

Article published online:
06 June 2025