Clinical History
A 17-year-old female without any prior history presented with a three week history of exertional dyspnoea and palpitations. She was asymptomatic at rest. Other than a persistent sinus tachycardia, examination was unremarkable. Baseline laboratory investigations did not reveal any abnormality.
Imaging Findings
The initial chest radiograph (Figure 1) shows cardiomegaly with a rounded contour suggestive of a pericardial effusion, and blunting of the costophrenic angles in keeping with pleural effusions.
Subsequent CTPA (Figure 2) revealed a large soft tissue mass in the anterior and superior mediastinum encasing the aorta, its branching vessels and also the left main bronchus. The mass was causing severe luminal narrowing of the right pulmonary artery. There was also a large pericardial effusion with evidence of cardiac congestion - consistent with a cardiac tamponade.
The patient went on to have CT-guided biopsy (Figure 3) and was ultimately diagnosed with myeloid sarcoma. The initial treatment was with high dose intravenous dexamethasone and systemic chemotherapy and subsequent to this a repeat CT thorax was obtained (Figure 4), with measurable reduction in the size of the soft tissue mass and improvement in the calibre of the right pulmonary artery.
Discussion
Myeloid sarcoma is a rare manifestation in which a tumour composed of myeloid blast cells occurs at a site other than the bone marrow [1]. It occurs most commonly in patients with acute myeloid leukaemia, however, can also be seen in patients with chronic myeloid leukaemia and myelodysplastic syndromes. Rarely de novo myeloid sarcoma without underlying malignancy can occur [2] (as in this case). The most common extramedullary locations include the skin, bone and lymph nodes. Mediastinal involvement is rare and described only in case reports [3].
The patient presented to the emergency department and unusually, initial laboratory investigations were normal. The first clue to the diagnosis was provided by an abnormal chest radiograph. Subsequent cross-sectional imaging of the thorax diagnosed a large mediastinal mass, revealing its precise anatomical location and the extent of invasion into adjacent structures. CT guided core biopsy was essential to determine a histopathological diagnosis.
Following tissue diagnosis, the patient was treated with high dose intravenous steroids and systemic chemotherapy (daunorubicin and cytosine arabinoside). A short interval CT Thorax demonstrated a significant treatment response with a measurable decrease in the size of the tumour. The patient is now four months post initial presentation and has just undergone allogeneic bone marrow transplant having completed the initial course of chemotherapy. The overall prognosis of this condition is poor.
Differential Diagnosis List
Myeloid Sarcoma
Lymphoma
Germ cell tumour
Thymic neoplasm
