Renal cell carcinoma presenting with a bone metastasis

Clinical History

This 56 year-old female was referred with vague knee pain to her GP for which an outpatient radiograph was performed. Two months later with increasing pain, full length tibia/fibula films were performed. The patient had no other complaints and no other significant medical or surgical history.

Imaging Findings

The first AP radiograph of the knee (Fig. 1) (in retrospect) shows subtle changes in bony architecture in the proximal tibial metaphysis with a wide zone of transition. No expansion or cortical destruction is evident.

On the additional plain film 3-months later (Fig. 2) the lesion was more apparent with significant progression of a now largely lucent metaphyseal lesion, with expansion and destruction of the medial cortex. MRI of the tibia and fibula (Fig. 3) confirmed a large hypervascular destructive bone lesion with central necrosis in the tibial metaphysis, highly suggestive of a bony metastatic deposit.

CT was performed to locate a primary malignancy (Fig. 4). A huge mass was present in the upper pole of the right kidney, with a large amount of central necrosis. There was evidence of tumour thrombus into the right renal vein and effacement of the IVC. No contra-lateral renal lesion was present.

Ultrasound-guided biopsy of the renal mass was performed.

Discussion

Background

Renal cell carcinoma (RCC) is the commonest form of kidney tumour. In 20% of cases it is multicentric within the same kidney and in 2% is bilateral. ¹
RCC's account for 3% of adult malignancies and has a male predominence, typically presenting in the 6th and 7th decades of life.

Clinical Perspective

Risk factors for RCC include; smoking, chemical exposure and a genetic predisposition, in particular those with Von Hippel-Lindau disease.

The commonest method of presentation (> 50%) is now as an incidental finding on imaging performed for other purposes.

Alternative presentations include; haematuria, flank pain, or less likely a loin mass and weight loss. Paraneoplastic symptoms are present in up to 40% at some stage during the course of the disease.²

The histologic subtype of RCC also predicts the development of metastatic disease and so prognosis. The Heidelberg classification identifies five distinct malignant histologic subtypes: conventional (clear cell) (75%), papillary (15%), chromophobe (5%), collecting duct (2%), and RCC unclassified. Although some metastatic sites are more likely with certain histological subtypes, bone metastases do not have a preponderance, occuring in 7-11% in all subtypes.³

Imaging Perspective

RCC's are typically exophytic, with heterogenous, but hypervascular appearances. Tumour extension into the renal vein is common. If required, most lesions are amenable to image-guided percutaneous biopsy. Metastases occur commonly to lung, bone, liver, brain. Metastatic deposits typically exhibit the same hypervascular characteristics as the primary tumour. Bony metastases from renal cell carcinoma are typically lucent, expansile and can be highly destructive. The most malignant bony deposits demonstrate a permeative growth-pattern that may give only subtle changes in the bony architecture on plain film. A radio-isotope bone scan is normally only performed in those with bone pain or raised ALP (bone).

Outcome

Treatment is surgical, with nephrectomy or in the case of peripheral tumours, less than 5 cm with no locoregional disease 'nephron sparing surgery' in the form of a partial nephrectomy. There is growing interest/use of percutaenous ablative approaches, such as radiofrequency heat ablation or cryoablation in selected groups, such as poor surgical candidates.⁴

Those presenting with Stage 1 tumours have a 95% 5 year survival rate.

Take Home Messages

1. With an aggressive bone lesion, always think metastasis and search for a primary

2. With an expansile aggressive lucent bone lesion, think of a primary renal cell malignancy

3. For centrally necrotic tumours biopsied under image guidance, one should target the approach to biopsy the rim, to enable a histologically conclusive outcome.

Differential Diagnosis List

Final Diagnosis

Bone metastasis due to renal cell carcinoma

URL:	https://www.eurorad.org/case/9533
DOI:	10.1594/EURORAD/CASE.9533
ISSN:	1563-4086