UNDIFFERENTIATED PLEOMORPHIC SARCOMA OF THE SCALP WITH CERVICO-FACIAL EXTENSION MIMICKING SEVERE PYOGENIC CELLULITIS: A CASE REPORT HIGHLIGHTING THE COST OF DIAGNOSTIC DELAY

Background: Undifferentiated pleomorphic sarcoma (UPS), formerly malignant fibrous histiocytoma, is the most common soft tissue sarcoma of late adulthood but only rarely arises in the head and neck. Because of its nonspecific inflammatory appearance, cutaneous fistulization and secondary bacterial colonization, cervico-facial UPS can closely mimic a pyogenic soft-tissue infection, delaying histological diagnosis until the disease has become locally advanced or metastatic.
Case presentation: We report a 69-year-old woman with a two-month history of a progressive left fronto-parieto-temporal scalp mass and left cervico-facial edema, initially treated abroad as a refractory abscess with surgical drainage and broad-spectrum intravenous antibiotics (imipenem and vancomycin), without improvement. On referral, cervico-facial computed tomography (CT) demonstrated a large (62 × 80 × 160 mm), locally invasive soft-tissue mass of the scalp and neck with multilevel necrotic cervical lymphadenopathy, extension to the parapharyngeal space, compression of the internal jugular vein, and infiltration of the sternocleidomastoid muscle. Thoraco-abdomino-pelvic CT showed bilateral iliac and vertebral osteolytic lesions, a small pericardial effusion, and two indeterminate hepatic hypodensities. Histopathology of the scalp mass and cervical/supraclavicular lymph nodes revealed a highly pleomorphic spindle- and giant-cell tumor. Immunohistochemistry showed absence of AE1/AE3, EMA, CD3, CD20, CD34, desmin, myogenin and S100, with preserved nuclear INI-1 and moderate diffuse nuclear TLE-1 positivity, supporting undifferentiated pleomorphic sarcoma. Three of four excised lymph nodes were tumor-positive with capsular rupture, confirming nodal metastasis. Given the extent of locoregional and probable distant disease at diagnosis, the multidisciplinary tumor board oriented the patient toward palliative care; she died a few weeks later.
Conclusion: This case illustrates how cervico-facial UPS can convincingly mimic a non-resolving pyogenic infection, and how the resulting diagnostic delay can allow an initially localized tumor to progress to inoperable, metastatic disease within weeks to months. Failure to respond to adequate antibiotic therapy and drainage, a progressively enlarging mass, and necrotic lymphadenopathy on imaging should prompt early biopsy. Earlier recognition might have allowed treatment while the disease was still surgically resectable, underscoring that timely histological diagnosis, not the biological aggressiveness of UPS alone, was the modifiable determinant of this patient's outcome.