Myeloid sarcoma or chloroma, an extramedullary myeloid tumor, is observed in a minority of patients with acute non-lymphocytic leukaemia. Very few cases may present without bone marrow involvement (i.e., primary myeloid sarcoma). Among the various sites of disease manifestation reported, solitary bone lesions may occur. Diagnosis and, even more so, assessment of response to systemic therapy is strikingly more difficult than in systemic disease, i.e. acute leukaemia. We report the case of a patient diagnosed with primary myeloid sarcoma involving thoracic vertebral bones and associated with spinal cord compression. Here, positron emission tomography/computer tomography imaging allowed assessment of the initial extent of the disease as well as the response to a combined radiochemotherapeutic approach.

A male, 60 years old patient presented with pain in the flanks extending to the left leg. MRI imaging revealed an intraspinal mass in close proximity to the eleventh thoracic vertebral bone. Surgical resection of the mass including biopsy of the vertebral bone allowed the histopathological diagnosis of a myeloid sarcoma. Upon presentation, the assessment of bone marrow and meningeal involvement yielded negative results. MRI imaging revealed changes suggestive of residual manifestations albeit remaining inconclusive with regard to an enhancement secondary to the surgical intervention.

PET/CT imaging revealed a distinct signal located to the eleventh vertebral bone as a result of enhanced metabolic turnover (SUV 8.8) that was interpreted as active myelosarcoma tissue. Induction chemotherapy was initiated consisting of high-dose Ara C and Mitoxantrone (HAM). Following induction therapy, PET/CT assessment showed no change in metabolic activity. Extended field radiation therapy was performed, involving the two adjacent upper and lower vertebral bones, with a total dose of 30 Gy. This time, response assessment via PET/CT showed only a slight enhancement in metabolic turnover, suggestive of remission. As a consolidation, high dose Ara C therapy was initiated. Until now the patient is fine and shows no sign of residual myeloid sarcoma.

PET/CT in this case was the only method which reliably allowed the assessment of tumor location, extent and activity in a previously operated vertebral bone and, as a tool for the assessment of response, was guiding therapeutic decisions. In our opinion, the exposure to substantial radiation exposure due to PET/CT imaging is outweighed by the obvious diagnostic benefit.

Disclosures: No relevant conflicts of interest to declare.

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