A cellular dermatofibroma is a common, non-cancerous skin growth. It is a specific subtype of dermatofibroma. This lesion originates in the dermis, the layer of skin beneath the epidermis.
What is Cellular Dermatofibroma?
Cellular dermatofibromas present as firm, reddish-brown to tan nodules, measuring between 0.5 to 1.5 centimeters in diameter. They can appear slightly raised or subtly depressed on the skin surface. A characteristic feature is the “dimple sign,” where the lesion indents inward when gently squeezed from the sides.
These growths form from a proliferation of fibroblast-like cells and histiocytes within the dermis. While they can arise spontaneously, their development can be associated with minor skin trauma, such as an insect bite, a splinter, or a ruptured hair follicle. The term “cellular” distinguishes this variant from common dermatofibromas due to an increased density of these spindle-shaped cells.
The heightened cellularity means there are more cells packed together, with less intervening collagen fibers, compared to a typical dermatofibroma. This can make the lesion appear more aggressive under initial microscopic review or clinically.
The resemblance to certain malignant soft tissue tumors, such as dermatofibrosarcoma protuberans (DFSP) or atypical fibroxanthoma, is concerning. Therefore, the “cellular” designation highlights the need for careful evaluation and a thorough pathological assessment to ensure an accurate diagnosis.
Identifying and Diagnosing Cellular Dermatofibroma
Identifying a cellular dermatofibroma begins with a clinical examination by a dermatologist. The physician assesses the lesion’s size, color variations (brown, red, or purple), and texture. The presence of the “dimple sign,” where the lesion retracts inward when pinched, is a helpful indicator.
A definitive diagnosis relies on obtaining a tissue sample through a biopsy. This might involve a punch biopsy, which removes a small cylindrical core of tissue, or an excisional biopsy, where the entire lesion is surgically removed.
A dermatopathologist then examines the biopsy under a microscope, looking for specific features. They identify a non-encapsulated lesion within the dermis, composed of intersecting bundles of spindle cells. The increased cellularity, arranged in a storiform (pinwheel-like) or haphazard pattern, is a hallmark of this subtype. The pathologist also notes the presence of trapped collagen bundles at the periphery and evaluates any mitotic activity, which remains low.
The differentiation from other skin lesions is an important aspect of diagnosis. Due to its heightened cellularity, cellular dermatofibroma must be carefully distinguished from malignant tumors like dermatofibrosarcoma protuberans (DFSP). DFSP invades deeper into the subcutaneous fat and stains positive for CD34, a marker not expressed in dermatofibromas. Distinguishing it from atypical fibroxanthoma, another spindle cell tumor, relies on specific immunohistochemical markers and the overall architectural pattern of the lesion.
Treatment Approaches and Outlook
For small cellular dermatofibromas that are asymptomatic and confirmed benign, observation is a suitable approach. If the lesion is not bothersome or cosmetically unappealing, immediate active intervention may not be necessary. This allows the patient to monitor the lesion.
Complete surgical excision is the most common and definitive treatment, especially when the lesion is symptomatic, growing, or if the patient prefers removal for cosmetic reasons. This also provides the opportunity for a thorough pathological examination of the specimen, confirming the benign diagnosis.
Cellular dermatofibromas have a higher potential for local recurrence compared to common dermatofibromas. This increased likelihood is attributed to their ill-defined borders and a tendency to infiltrate the surrounding dermal tissue. If any portion of the lesion is left behind after the initial excision, it may regrow in the same area.
Despite the possibility of local recurrence, cellular dermatofibromas are considered benign tumors. They do not spread to distant parts of the body (metastasize), nor do they transform into malignant forms of cancer. The long-term prognosis following diagnosis and appropriate management is excellent. In instances where there is concern about recurrence, such as when initial surgical margins were very close, dermatologists may recommend periodic follow-up visits.