From the Guidelines
An exophytic renal cyst is a benign, fluid-filled sac that develops on the outer surface of the kidney, protruding outward from the kidney's contour, and can be characterized by its location and benign features on imaging studies, such as MRI, which has high specificity for small cysts 44. When evaluating renal lesions, MRI is frequently used to characterize them, and its specificity is significantly higher than that of CT in diagnosing renal cell carcinoma (RCC) 25. The diagnosis of an exophytic renal cyst can be made using MRI without and with IV contrast, and even noncontrast T2-weighted imaging can provide diagnostic information, such as homogeneous and very high T2 signal intensity for simple cystic lesions 53. Some key features that can help differentiate benign exophytic renal masses from malignant masses include an angular interface with the renal parenchyma on T2-weighted imaging, which has been shown to be 78% sensitive and 100% specific for benign masses 55. Exophytic renal cysts are common findings on imaging studies and are often discovered incidentally during examinations for other conditions, and most are simple cysts that contain clear fluid and have thin, smooth walls without internal structures, and generally don't require treatment unless they cause symptoms 44, 53. The use of diffusion-weighted imaging and other specialized MRI sequences may also have some ability to differentiate solid RCC from oncocytomas and characterize the histologic subtypes of RCC 56, 57. In general, the management of exophytic renal cysts depends on their size, location, and whether they cause symptoms, and while most are harmless, complex cysts with irregular features may require further evaluation to rule out malignancy 1.
From the Research
Definition of Exophytic Renal Cyst
- An exophytic renal cyst is a type of renal cyst that grows outward from the kidney, extending into the surrounding tissue or space 2.
- Exophytic renal masses are more likely to be of lower pathologic grade and of the papillary RCC subtype when compared with endophytic renal tumors 2.
Characteristics of Exophytic Renal Cysts
- Exophytic renal cysts can be differentiated from other types of renal cysts based on their radiologic characteristics, such as their location and extent of growth into the kidney 2.
- The Bosniak classification system is a valuable tool for characterizing renal cysts, including exophytic renal cysts, and determining their potential for malignancy 3, 4, 5.
Diagnosis and Management of Exophytic Renal Cysts
- The diagnosis of exophytic renal cysts typically involves imaging studies, such as computed tomography (CT) or magnetic resonance imaging (MRI), to characterize the cyst and determine its potential for malignancy 3, 5.
- The management of exophytic renal cysts depends on their characteristics and potential for malignancy, and may include watchful waiting, ablative therapies, or surgical intervention 2, 6.