Background: Adult-onset or recurrent subcutaneous hemangiomas of massive proportions are exceedingly rare clinical entities. When these benign vascular anomalies present with rapid growth, massive dimensions, overlying cutaneous ulceration, and radiological features denoting hypervascularity and flow voids, they clinically and radiologically mimic aggressive vascular malignancies such as angiosarcoma or hemangiopericytoma.

Case Presentation: We report the case of a 35-year-old male who presented with a massive, rapidly progressive, and intensely painful recurrent mass over the posterosuperior aspect of the left shoulder. The lesion had been previously excised in 2024 and diagnosed as a benign hemangioma. However, its aggressive clinical recurrence within 18 months, coupled with magnetic resonance imaging (MRI) revealing profound heterogeneity, cutaneous ulceration, and prominent axillary lymphadenopathy, raised high suspicion for malignant transformation. The patient underwent a radical wide local excision with 2 cm margins and axillary lymph node sampling, followed by immediate complex reconstruction utilizing a pedicled latissimus dorsi (LD) myocutaneous flap and a split-thickness skin graft (STSG). Final histopathological examination confirmed a benign hemangioma with complete margin clearance and reactive, tumor-free axillary lymph nodes.

Conclusions: This case underscores the diagnostic dilemma posed by aggressive, recurrent benign vascular lesions mimicking sarcomas. It highlights the imperative for radical oncologic clearance despite benign histories, and demonstrates the efficacy of regional pedicled flaps in reconstructing massive shoulder defects to ensure functional and aesthetic preservation.

KEYWORDS: Hemangioma, Vascular Neoplasm, Angiosarcoma Mimic, Latissimus Dorsi Flap, Wide Local Excision, Reconstructive Surgery, Soft-tissue Sarcoma.