Casting a wider net: Mohs micrographic surgery for retiform hemangioendothelioma

Retiform hemangioendothelioma (RH) is a rare vascular tumor that has low metastatic potential but is locally aggressive. Wide excision is the standard. However, the local recurrence rate is 60% despite surgery.1 In the literature, there has been only one published case of RH treated with Mohs micrographic surgery (MMS), but on the distal phalanx.2 We report a case of RH on the lower leg treated successfully with MMS. We present a 20-year-old female with a red plaque on the left pretibial area. Six months prior, the lesion began as a pinkish patch, presumably 0.3 × 0.3 cm, that she recalls having sustained minor blunt trauma while exiting a pool. In 2 months, it grew into a plaque with irregular borders, prompting a consult. Despite a shave biopsy, recurrence was seen in a week. Histopathology revealed a dermal vascular neoplasm with dilated branching vessels containing intravascular papillary projections. Immunohistochemistry was positive for EGR (Figure 1), CD34, and CD31; Ki-67 stained rare cells, actin identified pericytes around all vascular structures, and negative for HHV-8, CK AE1/AE3, and podoplanin. Non-contrast MRI revealed an 8 mm nodular skin thickening with reticular subcutaneous edema without muscle or fascial extension. A diagnosis of RH was concluded and subsequently referred to our department for surgery. Upon examination, we noted a 1.0 × 1.0 cm red plaque on the left shin, surrounded by blanchable livedo-reticularis-like patches (Figure 2, inset). The first stage of Mohs was taken with a 0.5 cm margin, depth down to the fascia (Figure 2). This returned clear on all sections examined, cross-referenced with initial biopsy slides. The post-operative defect was 2.6 × 2.0 cm, and repaired with an S-plasty closure. The patient's parents were informed to contact us about any suspicion of recurrence. They have not contacted our clinic in the 10 months since surgery as of writing. Retiform hemangioendothelioma was categorized by the International Society for the Study of Vascular Anomalies as a locally aggressive borderline vascular tumor.3 Diagnosis is challenging as it may resemble other vascular tumors like hemangioma, Dabska tumor, Kaposi sarcoma, and angiosarcoma. Histopathology shows dermal arborizing blood vessels extending between collagen bundles, resembling the rete testis. The vessels are lined by uniform endothelial cells with prominent nuclei and scanty cytoplasm, bulging into the vascular lumen like hobnails. Special stains are positive for endothelial and vascular markers of EGR, CD34, and CD31 and negative for HHV-8 and podoplanin.3 As this tumor is rare, no treatment guidelines are in place. The current recommendation is surgical excision with tumor-free margins and long-term follow-up. However, most reports only mentioned wide local excision, and the exact margins used were not disclosed. Choi et al.4 performed the procedure with a 3 mm margin, only for the tumor to recur 2 months later. Keiler et al.2 reported the first case of MMS done for RH was on the left distal fourth finger in an 11-year-old girl, which saved the digit from potential amputation. The 5-month follow-up showed no recurrence. They noted that recurrence typically occurs within 2–36 months from wide excision. Given the locally aggressive nature of this tumor, infiltrative histology, and high recurrence rates with standard excision, MMS should be preferred over wide excision since it can ensure clear peripheral and deep margins. As for our patient who presented with a well-defined tumor, margins could be kept more conservative. However, since the tumor recurred quickly after the shave biopsy, it was decided that a more adequate margin of 0.5 cm be taken, similar to cases of dermatofibroscaroma protuberans.5 More evidence is needed to make broader clinical guidelines for these types of rare tumors. We suggest the establishment of Mohs micrographic surgery as a potential treatment in select cases.