Melanotrichoblastoma: A Rare Pigmented Variant of Trichoblastoma
Trichoblastomas are rare cutaneous tumors arising from the hair bulb and mesenchyme. Although they are benign, they can pose a diagnostic dilemma for the clinician and pathologist because they clinically and histologically mimic more common lesions such as basal cell carcinomas (BCCs) and trichoepitheliomas. It is important for the clinician and pathologist to be aware of such tumors and their variants. We present a case of a melanotrichoblastoma, an exceedingly rare variant of trichoblastoma, as well as review the current literature on the clinical presentation and histologic differentiation of these unique tumors with their more commonly seen mimics.
Practice Points
- Pigmented trichoblastoma is a histologic variant of trichoblastoma characterized by the presence of melanin pigment.
- At least some pigmented trichoblastomas contain melanocytes and have been referred to as melanotrichoblastomas.
- The presence of melanocytes within pigmented trichoblastomas should not be confused as representing an example of colonization or a collision tumor.
Conclusion
Trichoblastomas are uncommon tumors of germinative hair bulb origin that can have several histologic variants. A well-documented subtype of trichoblastoma characterized by melanin deposits within and around tumor nests has been identified and classified as a pigmented trichoblastoma. Four cases of melanotrichoblastoma have been reported and represent a variant of a pigmented trichoblastoma characterized by the presence of melanocytes within the lesion. Whether they represent a true variant is of some debate and additional study is required. Although these tumors are exceedingly rare, it is important for the clinician and pathologist to be aware of this entity to prevent confusion with other similarly appearing follicular lesions, most notably BCCs, because of the difference in treatment and follow-up.
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