Imaging for the diagnosis and response assessment of renal tumours

Abstract

Purpose: Imaging plays a key role throughout the renal cell carcinoma (RCC) patient pathway, from diagnosis and staging of the disease, to the assessment of response to therapy. This review aims to summarise current knowledge with regard to imaging in the RCC patient pathway, highlighting recent advances and challenges.

Methods: A literature review was performed using Medline. Particular focus was paid to RCC imaging in the diagnosis, staging and response assessment following therapy.

Results: Characterisation of small renal masses (SRM) remains a diagnostic conundrum. Contrast-enhanced ultrasound (CEUS) has been increasingly applied in this field, as have emerging technologies such as multiparametric MRI, radiomics and molecular imaging with ^99mtechnetium-sestamibi single photon emission computed tomography/CT. CT remains the first-line modality for staging of locoregional and suspected metastatic disease. Although the staging accuracy of CT is good, limitations in determining nodal status persist. Response assessment following ablative therapies remains challenging, as reduction in tumour size may not occur. The pattern of enhancement on CT may be a more reliable indicator of treatment success. CEUS may also have a role in monitoring response following ablation. Response assessments following anti-angiogenic and immunotherapies in advanced RCC is an evolving field, with a number of alternative response criteria being proposed. Tumour response patterns may vary between different immunotherapy agents and tumour types; thus, future response criteria modifications may be inevitable.

Conclusion: The diagnosis and characterisation of SRM and response assessment following targeted therapy for advanced RCC are key challenges which warrant further research.

Keywords: Diagnosis; Imaging; Renal cancer; Staging; Treatment response.

Fig. 1

Ultrasound (a) and CT (b) appearances of a simple cyst with a thin imperceptible wall and posterior acoustic enhancement and no internal echoes or enhancement (Bosniak I). Contrast this to the ultrasound (c) and CT (d) features of a clear cell renal cell carcinoma with ill-defined borders and solid mixed echogenicity replacing renal parenchyma and avid contrast enhancement with areas of low attenuation tumoral necrosis on CT

Fig. 2

Non-enhanced (a) and split-bolus post-contrast nephrographic/urographic phase images (b) with a circular region of interest centred on a 3 cm left interpolar low attenuation renal mass demonstrating definite internal enhancement (Hounsfield units increasing from 27 to 62). This was confirmed as a type 1 papillary renal cell carcinoma

Fig. 3

Classical ultrasound (a) and CT (b) appearances of a left renal angiomyolipoma. Solid hyperechoic mass relative to renal parenchyma and of fat attenuation on CT with enhancing components

Fig. 4

Coronal portal venous phase CT depicting a large left lower pole renal tumour (star) with direct extension into the renal vein (arrowheads) and along the gonadal vein (filled arrow). Coronal fat-saturated T1 weighted MRI images following intravenous gadolinium in a different case demonstrate enhancing tumour thrombus within the left renal vein and extending into the infradiaphragmatic vena cava (stage T3b)

Fig. 5

Sagittal T1 weighted MRI (a) and CT (b) images of the thoracolumbar spine demonstrating metastatic infiltration at L4 and T12 with an associated pathological fracture and narrowing of the central vertebral canal

Fig. 6

Images (a) baseline and (b) depict the 31% reduction in size of a right renal tumour over the course of 12 weeks targeted therapy, meeting criteria of partial response by RECIST v1.1. Conversely, images (c) at baseline and (d) in a different patient show that though there is clear devascularisation of the right renal primary tumour on treatment with a reduction in central enhancement, there is insufficient reduction in size to amount to a partial response by RECIST v 1.1 assessment