Monoblastic sarcoma of the kidneys in an infant leukaemia

An 8-month-old Japanese boy was diagnosed with acute monocytic leukaemia [AMoL, M5b according to French–American–British (FAB) classifications] with t(9;11)(p22;q23). Abdominal magnetic resonance imaging demonstrated a homogeneous solid mass (25 · 36 · 25 mm) in the upper pole of the left kidney (Fig. 1A) and a cortical mass (diameter, 10 mm) in the lower portion of the right kidney. Renal masses were hypointense relative to renal cortex on both T1and T2weighted imaging, with weak homogeneous gadolinium enhancement. Histopathological examination of creamcoloured biopsy sections revealed diffuse infiltration of cells surrounding intact glomeruli in the renal parenchyma (Fig. 1B). Predominant monoblastic features were shown on imprints (Fig. 1C). Fluorescence in situ hybridisation and Southern blot analyses identified the rearrangement of mixed-lineage leukaemia (MLL) gene, confirming a diagnosis of monoblastic sarcoma of the kidney. Monoblastic sarcoma is a less-common form of myeloid sarcoma, and may precede or occur concurrently with AMoL with 11q23/MLL rearrangements. Any part of the body can be involved, but renal involvement is rare and no cases of infants have previously been reported. In cases such as the present, pathologically confirmed diagnosis is essential to establish appropriate therapeutic strategies, as the differential diagnosis could include primary renal tumours.