Clinicopathological and Dermoscopic Features in a Case of Linear and Unilateral Basaloid Follicular Hamartoma.

Linear and unilateral basaloid follicular hamartoma (BFH) is a rare disease that manifests with papules and plaques with distribution along lines of Blaschko. It runs a benign course but with the risk of basal cell carcinoma (BCC) in long term course. BCC can be differentiated from BFH with histopathology and immunohistochemistry. Dermoscopic features of BCC are well studied. Dermoscopic features of BFH are not yet described in literature in detail probably due to rarity of the disease. Here, we present a case of extensive linear and unilateral BFH with its clinicohistopathological and dermoscopic features. The lesions were extensive to involve scalp, face, neck, upper, and lower trunk. Dermoscopy revealed features similar to that of BCC including brown-grey globules and dots, in focus dots, brown linear and arciform structures, crown vessels, short fine telangiectasias, spoke wheel like structures without central dark point, white structureless areas with telangiectasias and keratotic plug. Other dermoscopic features of BCC like arborizing vessels, blue-grey ovoid nests, maple leaf-like areas, concentric structures, ulcerations, erosions and white streaks were absent in this case. Copyright:

Introduction

Basaloid follicular hamartoma (BFH) presents as nodule or plaque showing differentiation towards germinative cells of the hair follicle. Characteristic histopathology of BFH is the presence of branching cords of undifferentiated anastomosing basaloid and squamoid proliferations connected to the overlying epidermis. We report a case of blaschkoid unilateral BFH involving scalp, face, and trunk and describe dermoscopic features of the same. Most of the reported cases had one or two plaques or linear streaks of papules. Our patient presented with extensive involvement of left hemi face and trunk with more than ten linear streaks. Less than 20 cases of linear and unilateral BFHs are reported in English literature till date.[1]

Case History

A 14-year old male presented with multiple discrete dome shaped shiny papules coalescing to form plaques at places. The lesions were present on left side of scalp, face, and trunk in linear distribution along lines of Blaschko [Figure 1a and b]. A linear skin coloured plaque was present on pre auricular area [Figure 1a]. The lesions were strictly confined to the left side of the body except in the neck and lumbar area where they crossed midline. Patient had dorsal scoliosis and a café au lait macule in the lumbar region. Some of the papules and plaques were skin coloured while others were hyperpigmented. A few papules had black hyperkeratotic plug in the centre [Figure 1c]. Most of the scalp lesions were coalescing with each other to form a boggy plaque with some yellowish hue at places. Hair density was reduced on the affected areas of scalp. The lesions were present since birth with gradual increase in their size. There was no family history of similar condition or history of consanguinity in parents.

Figure 1

(a) Papules and plaques in linear and unilateral Blaschkoid streaks involving left side of face and neck. (b) Similar lesions over left side of trunk. (c) Multiple skin coloured as well as pigmented papules in groups with central plugs and dells

Dermoscopy of trunk and face lesions showed well-defined rounded structures that contained brown-grey linear and arciform structures, brown-grey globules and dots, in-focus dots, spoke wheel like structures without central dark point and brown-black keratotic plugs [Figure 2]. There were well-defined rounded structures containing structureless areas with short fine telangiectasias [Figure 2] and irregularly branched crown vessels [Figure 3]. Scalp lesions showed yellowish brown follicular keratotic plugs, non-uniform reduction in hair follicular unit density, number of hair shafts per follicular unit and short fine telangiectasias.

Figure 2

Well defined round areas containing Brown grey globules (black arrow) and dots (white arrow), brown black keratotic plug (red arrow), in focus dots (purple arrow), spoke wheel like structures without central dark point (blue arrow), short fine telangiectasias (green arrow), white structureless areas (yellow arrow)[Oitez escope, 10X, Polarized light mode]

Figure 3

Round structure with irregularly branched crown vessels (arrows) [Oitez escope, 200X, Polarized light mode]

Histopathology showed circumscribed nodules and epithelial proliferations that were connected with surface epidermis, and follicular infundibula. The proliferation showed reticulate and cord like pattern branching out from a follicular infundibulum [Figure 4]. Cells making up the proliferating epithelium were basaloid with melanin pigment predominantly seen in the peripheral basaloid bud like proliferations. The stroma was fibrocytic. There were clefts in stroma but none separating epithelium from stroma [Figure 5]. Due to lack of resources we could not perform immunohistochemistry in our case.

Figure 4

Circumscribed nodules and epithelial proliferations that are connected with surface epidermis and follicular infundibula. The proliferation shows reticulate and cord like pattern branching out from a follicular infundibulum (H and E 10X)

Figure 5

Cells making up the proliferating epithelium are basaloid. Basaloid cells with melanin pigment predominantly seen in the peripheral basaloid bud like proliferations. The stroma is fibrocytic. There are clefts in stroma but none separating epithelium from stroma. Inset showing lack of cytological atypia (H and E 100X)

Considering clinical, histopathologcal and dermoscopic features, diagnosis of linear and unilateral basaloid follicular hamartoma was made. Considering the benign nature of the present lesions and the risk for developing BCC in future, regular follow up was advised.

Discussion

Basaloid follicular hamartoma was first described as a separate clinical entity distinct from BCC by Brown et al. in 1969.[2] The clinical features, associations, histopathological and immunohistochemistry features of BFHs are well described in English literature.[13]

Dermoscopy findings in BFH are not satisfactorily studied in order to define diagnostic features. Known features are bluish structureless areas,[4] lesion with globular pattern; white, pink, and grey areas and the presence of comedo-like openings and milia-like cysts.[5]

Basal cell carcinoma mimics BFH clinically as well as histopathologically. Dermoscopic criteria for basal cell carcinoma by Lallas et al.[6] include arborizing vessels, superficial (short) fine telangiectasias, blue–grey ovoid nests, multiple blue–grey globules, in-focus dots, maple leaf-like areas, spoke wheel areas (radial projections converging at a darker central point), concentric structures, ulceration, multiple small erosions, shiny white-red structureless areas and white streaks.

Wozniak-Rito et al. grouped these features into vascular, pigment related and non-vascular non-pigment related features.[7]

Since we found well defined rounded structures that contained brown-grey linear and arciform structures, brown-grey globules and dots, in focus dots, spoke wheel like structures without central dark point, brown-black keratotic plug, irregularly branched crown vessels, short fine telangiectasias and structureless areas with telangiectasias, we propose that these findings can’t be used to differentiate between BFH and BCC. Other findings like arborizing vessels, Blue grey ovoid nests, ulcerations, erosions, spoke wheel areas (radial projections converging at a darker central point), concentric structures and white streaks may be helpful for the same. We need further studies to confirm these observations.

White red structureless areas are due to fibrosis in the dermis and tumour stroma. White streaks are due to dermal fibrosis. The horizontal arrangement of increased number of collagen bundles parallel to epidermis are seen as whites streaks under dermoscope. Globules are due to basaloid tumour cell aggregates in the papillary dermis and/or reticular dermis. Spoke wheel structures are due to basalioma cells arranged in cords with radial growth from a central core.[8] Blue-grey globules and dots are due to presence of solid pigmented epithelial nests in papillary dermis. Short fine telangiectasias are due to dilated blood vessels in papillary dermis.[9] Maple leaf like structures are due to multifocal tumour nests containing pigment aggregates, connecting to each other as well as to the epidermis with lobular extension. They are located in papillary dermis and sometimes in reticular dermis. Blue grey ovoid nests are well bordered tumour nests with small buddings at periphery. Pigment aggregates are seen inside the tumour nest and/or in the tumour stroma. They are located in the reticular dermis. Brown dots are due to pigment deposition at dermoepidermal junction and tumour nests connected by thin bands and located in papillary dermis. Blue white veil is due to deposition of melanocytes and/or melanophages in dermis with orthokeratosis, hypergranulosis and rarely parakeratosis above this area. Ulcerations in dermoscopy corresponds to break in continuity of epidermis in histopathology.[10]

BFH is a benign tumour which does not ulcerate or invade surrounding structures. They can be managed with excision, cryosurgery, or laser ablation. Ulcerated BFHs should be evaluated for BCC. Longterm follow-up is necessary to detect BCC in BFH.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.