Reported are two cases of oncogenic osteomalacia, each caused by a small mesenchymal tumor, with detailed assessment of the tumors by light microscopy, electron microsopy, and immunohistochemistry. One tumor was a primitive mesenchymal tumor with prominent giant cell and vascular components, and the second resembled the giant cell variant of soft parts chondroma. Osteoclast‐like, multinucleated giant cells and vascularity were prominent features in both tumors. Although the literature documents a histologically heterogeneous group of tumors as causing this syndrome, most have multinucleated giant cells and/or extensive vascularity. The high incidence of these two histologic features in this group of tumors suggests that either or both may be related to the pathogenesis and/or metabolic consequences of oncogenic osteomalacia/rickets.

Summary:Two patients presented with hypophosphataemic osteomalacia and were subsequently found to have small tumours of unusual histopathology and location causing the osteomalacia. Each tumour was found after an intensive search for occult masses. Studies of vitamin D metabolism and renal tubular function before and after surgery yielded further insight into the pathophysiology of oncogenic osteomalacia. These cases demonstrate that microscopic quantities of tumour are capable of causing the syndrome and further illustrate the high index of suspicion often necessary to locate causative tumours in patients with hypophosphataemic osteomalacia.

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Ultrasound examination of the kidneys with grey-scale imaging and colour Doppler ultrasound is the most common renal imaging modality. A few years ago, contrast-enhanced ultrasound (CEUS) emerged as a non-invasive perfusion imaging modality to evaluate the renal vessels and microvascularisation. These contrast media contain intravenous microbubbles (sulfur hexafluoride), which have no deleterious effect on renal function. Being free of iodine, they also pose no risk for the thyroid gland. CEUS of the kidneys is mainly used for the evaluation of renal cysts and the analysis of renal lesions suspicious for malignancy. Also this method is used to visualise inflammation as well as renal perfusion after trauma or infarction.

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