Pelvic sarcoma arising from chronic osteomyelitis

Gulmann et al reported on a case of chronic osteomyelitis presenting as a mass of the chest mimicking a soft tissue sarcoma.¹ The authors suggested that, although chronic osteomyelitis is a known cause of confusion with bone tumours, a definitive diagnosis is feasible by specific immunohistochemical staining.

However, the potential risk of transformation of chronic osteomyelitis into a malignant lesion is an unforgettable point both for the clinician and the pathologist.² Two years ago, we encountered a patient developing a rapidly aggressive sarcoma with an uncommon onset. He was a 23 year old man, with a 16 month history of chronic osteomyelitis of the left hip bone, referred to the urological department. Three years before, he had been involved in a road accident with a bilateral fracture of the thigh bone and left acetabulum. On admission to the ward the patient reported fever, dysuria, and suprapubic pain. Physical examination demonstrated an osteocutaneous fistula with foul smelling drainage on the lateral aspect of the left hip bone. On standard computed tomography a haemorrhagic mass causing bladder impression and connected with the fistula was found. A surgical exploration was performed with drainage of the septic tissue, and a 5 cm pelvic lymph node was excised from the left iliac chain for histological examination. Light microscopy showed a solid proliferation of spindle shaped cells, with a high mitotic index, associated with lymphatic aggregates and foci of necrotic tissue. Staining for S-100 protein, desmin, vimentin, and focal smooth actin was positive. The histological and immunohistochemical features of the pelvic node confirmed an undifferentiated sarcoma. The patient died three months postoperatively. Malignant lesions are rare complications of chronic osteomyelitis. As reported in a large series by McGrory et al,³ squamous cell carcinoma is by far the most common type of associated malignant disease, whereas sarcoma has been reported only rarely.⁴ The latency period between the onset of osteomyelitis and the development of neoplasia may be as short as one year, or it may be decades. In general, the neoplasia occurs in the osteomyelitic sinus or in a chronic draining fistula. The most frequent clinical findings of malignancy in chronic fistulating osteomyelitis are persistent foul discharge, pain, and bleeding.³ In this case, the osteocutaneous fistula was connected to the left iliac area where the sarcoma arose and spread to pelvic lymph nodes. In conclusion, even though chronic osteomyelitis may be a cause of difficult differential diagnosis with bone tumours, we would emphasise the need to maintain a high index of suspicion in a case of chronic osteomyelitis with an unusual presentation.