Carlos Nicolau, Laura Buñesch, Rafa Salvador, Blanca Paño, Daniel Vas, Daniel Corominas, Lledó Cabedo, Carmen Sebastià. Radiology Department. Hospital Clínic. Barcelona. Spain
1. To learn the MRI protocol and sequences to evaluate renal masses. 2. To learn the usefulness of MRI for the characterisation of renal cysts and solid renal
The detection of an incidental renal mass is common in the daily practice of a Department of Radiology. Different diagnostic possibilities arise depending whether the lesion is cystic or solid. Cystic lesions can be managed using the Bosniak classification, while the management of solid lesions mainly focuses on the differentiation between renal cancer and benign tumours such as fat-poor angiomyolipoma and oncocytoma. We present the MRI protocol, sequences and how to interprete the MRI studies to characterize renal masses including the evaluation of anatomical sequences, enhanced-sequences after the administration of Gadolinium-based contrast agents and Diffusion technique.
MRI protocol should include T1, T2, DWI and contrast-enhanced sequences.
An easy way to classify renal cysts is the Bosniak classification. The last update of 2019 incorporated the MR as one of the imaging techniques to evaluate renal cysts.It grades cysts depending on different features: presence, number and thickness of enhancing septa and presence, size and margins of enhancing nodules.
The Bosniak classification has incorporated in its update several definitions that help in the classification of complex cysts, differentiating between Bosniak II, IIF and III cysts depending on the thickness of septa and between Bosniak III and IV cysts depending on the margins and size of soft-tissue nodules.
Regarding the differentiation of solid masses the three most common are renal cell carcinomas (RCC), oncocytomas and angiomyolipomas. The detection of macroscopic fat (using a FAT-SAT sequence) is diagnostic of angiomyolipoma.
If there is no obvious macroscopic fat in a renal mass, the T1 sequence after the administration of Gadolinium-based contrast agent can help in the differential diagnosis. The most hypervacular lesions are clear cell-RCC and oncocytomas while most hypovascular lesions are usually fat-poor angiomyolipomas and mainly papillary RCCs. Other signs such as the presence of a central scar can help suggesting the presence of oncocytomas.
The combination of anatomic (T2, T1) sequences with functional ones (DWI and contrast enhanced-sequence) allows the differential diagnosis of solid renal masses and an accurate classification of renal cysts following the Bosniak classification.
Diffusion sequence can help in the differential diagnosis between benign and malignant lesions. Restricted diffusion is very suggestive of mailgnant lesions. However, some benign lesions such as renal abscesses and granulomatous inflammatory lesions can show restriction of the Diffusion. On the contrary small and well differentiated renal cancers can show absence of restricted Diffusion.