Epithelioid fibrous histiocytoma (EFH) is a distinctive, rare, benign mesenchymal tumor of the skin. While a variant of the more common fibrous histiocytoma (dermatofibroma), recent research highlights its unique characteristics.
Understanding Epithelioid Fibrous Histiocytoma
Epithelioid fibrous histiocytoma has traditionally been viewed as a morphological variant of cutaneous fibrous histiocytoma, or dermatofibroma. However, newer molecular studies suggest EFH might be a distinct entity due to specific genetic rearrangements involving the anaplastic lymphoma kinase (ALK) gene.
These growths appear as solitary nodules. While they can occur anywhere on the body, they are most frequently observed on the extremities and sometimes the trunk. EFH lesions are generally small, often measuring up to 1 centimeter in diameter. They typically grow as exophytic dermal nodules, meaning they tend to protrude outwards from the skin surface.
Under a microscope, EFH is characterized by large, polygonal or ovoid cells, referred to as “epithelioid” cells, which have abundant pale eosinophilic cytoplasm and vesicular nuclei. These cells are often arranged in sheets or nests, and can sometimes be surrounded by typical spindle-shaped fibroblasts. The presence of prominent small, thin, and thick-walled vessels is also a common microscopic feature. While the term “epithelioid” might suggest an epithelial origin, these cells are actually histiocytic in nature, appearing similar to epithelial cells due to their shape.
Recognizing Its Characteristics
Epithelioid fibrous histiocytoma presents as a firm nodule or papule. The appearance can vary, but they are often described as flesh-colored, red, or red-brown. These lesions are usually well-circumscribed and can have a smooth surface texture. Some may also appear polypoid, meaning they are stalk-like or mushroom-shaped.
The size of an EFH commonly ranges up to 1 cm. They are generally firm to the touch and can sometimes be mobile, depending on their depth within the skin. A characteristic feature observed in many cases is an “epidermal collarette,” where the surrounding epidermis appears to embrace or form a collar around the base of the lesion.
Associated sensations such as itching or tenderness are less common with EFH, as these lesions are often asymptomatic. However, some individuals might experience mild discomfort or pain. The clinical presentation, including color and feel, can sometimes lead to confusion with other skin lesions, including vascular growths or even certain melanocytic neoplasms.
Diagnosis and Treatment Approaches
A definitive diagnosis of epithelioid fibrous histiocytoma necessitates a tissue biopsy. A small sample of the lesion is removed and examined under a microscope by a pathologist. This microscopic analysis identifies characteristic epithelioid cells and other histological features.
Differentiating EFH from other skin lesions is an important aspect of diagnosis. The epithelioid cellular morphology can sometimes mimic other benign and malignant conditions, including certain vascular tumors, melanocytic neoplasms like Spitz nevi or melanomas, and even other types of sarcomas. Immunohistochemical staining, which uses antibodies to detect specific proteins in the tissue, can be a valuable tool in this differentiation, particularly the detection of ALK protein expression, which is often present in EFH.
The primary treatment for epithelioid fibrous histiocytoma is typically surgical excision. This involves the complete removal of the lesion. The goal of surgical removal is to ensure that the entire growth is taken out to minimize the chance of recurrence. The specific surgical approach can vary based on the lesion’s size and its location on the body.
Following complete surgical removal, the prognosis for EFH is generally favorable. These lesions are benign, meaning they are non-cancerous and do not spread to other parts of the body. Recurrence after complete excision is considered low, with reported rates typically ranging between 5% and 10% for cutaneous fibrous histiocytomas in general. Even in rare instances where a lesion might recur, it usually remains benign.