Background/Objectives: Cysts are the most common kidney lesions identified in patients undergoing abdominal imaging, with ultrasound (US) typically serving as the initial diagnostic tool. Contrast-enhanced ultrasound (CEUS) has emerged as a highly effective modality for the evaluation of cystic renal lesions, particularly when conventional B-mode ultrasound (US) or CE-CT are inconclusive. While simple renal cysts are readily characterised on US, cystic renal lesions require further assessment. Methods: The Bosniak classification, originally developed for CE-CT, remains the cornerstone for categorising cystic renal lesions, guiding management from surveillance to surgical intervention. Recent efforts to standardise CEUS-specific imaging parameters and adapt the Bosniak criteria aim to improve interobserver agreement, reduce subjectivity, and enhance diagnostic accuracy. Results: CEUS offers superior sensitivity for detecting slow blood flow and minimal vascularity within septa, wall or solid components, often outperforming CE-CT in real-time vascular assessment. However, the high sensitivity of CEUS can reveal additional septa or subtle enhancement, potentially leading to lesion overscoring, if the different sensitivity of CEUS and CT/MRI for detecting enhancement is not taken into account. CEUS also plays a crucial role in the follow-up of non-surgical cystic lesions, providing a radiation-free and cost-effective alternative for long-term monitoring. Certain scenarios, such as post-interventional changes, traumatic cystic rupture, or infected cysts, fall outside the scope of the Bosniak system and require careful clinical correlation. Conclusions: By integrating CEUS into the diagnostic pathway, sonologists can achieve accurate lesion characterisation, optimise patient management, and minimise unnecessary invasive procedures, reinforcing CEUS as an essential tool in the evaluation and follow-up of complex renal cystic masses.

Zinner syndrome is a rare congenital anomaly of the male genitourinary tract, characterized by the triad of unilateral renal agenesis, ipsilateral seminal vesicle cyst, and ejaculatory duct obstruction. Owing to its low prevalence and nonspecific clinical presentation, diagnosis is often delayed or incidental, with imaging playing a central role in detection and characterization. This study presents a narrative review with an illustrative case report, aiming to summarize the imaging features of Zinner syndrome, outline the main radiologic differential diagnoses of seminal vesicle cysts, and highlight common diagnostic pitfalls, with emphasis on cross-sectional imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI). The narrative review of the literature highlights that CT and MRI are essential for accurate anatomical localization, characterization of cystic content, and identification of associated genitourinary anomalies. MRI, in particular, provides superior soft-tissue contrast and is considered the reference modality for diagnosis and differential evaluation of male pelvic cystic lesions. Key differential diagnoses include Müllerian duct cysts, prostatic utricle cysts, and ejaculatory duct cysts. As an illustrative example, we report the case of a young adult male presenting with pelvic discomfort, infertility, and mild lower urinary tract symptoms. Imaging findings, including ultrasound and cross-sectional studies, demonstrated a seminal vesicle cyst associated with ipsilateral renal agenesis, consistent with Zinner syndrome. Zinner syndrome should be considered in the evaluation of male pelvic cystic lesions, particularly in the presence of unilateral renal agenesis. Awareness of its characteristic imaging features is essential for accurate diagnosis and appropriate management, with MRI playing a pivotal role in confirming the diagnosis and distinguishing it from other pelvic cystic entities.

Hydatidosis is an endemic, widely distributed anthropozoonosis that involves the liver, lungs, and other organs. We report two cases of large renal hydatid cysts. Diagnosis was suspected based on radiological examinations. The patients were given albendazole tablets 400 mg twice per day (one month before and one month after surgery), with monitoring of blood count and liver enzymes. During follow-up assessment for renal hydatid cysts, the possibility of recurrence must be kept in mind. These cysts can completely destroy the kidney.

Renal ectopia results from an abnormal arrest of renal ascent during embryonic development and is often associated with malrotation, unusual vasculature, and anomalies of the collecting system. Although numerous ectopic kidneys are asymptomatic and discovered incidentally, their variant anatomy holds clinical significance as it may interfere with imaging interpretation and surgical procedures. We present a case of a right iliac ectopic kidney identified during the routine dissection of an 82-year-old male donor. The kidney was located in the right iliac fossa and demonstrated marked anterior malrotation, a large extrarenal pelvis, a solitary aberrant artery originating from the right common iliac bifurcation and entering the superior pole, venous drainage into the right common iliac vein, and multiple cortical and medullary cysts. The contralateral kidney was situated in its normal position and was grossly unremarkable. This combination of positional, vascular, collecting-system, and parenchymal variations exemplifies the complexity of renal ectopia and underscores the importance of meticulous anatomical identification. Understanding these variants is essential for radiologists, surgeons, and anatomists, as failure to recognize an ectopic kidney may result in diagnostic errors or iatrogenic injury during pelvic and vascular interventions.

Compared with cancers of other organs, precursor lesions of renal cell neoplasms are rarely discussed. However, there are specific scenarios where cysts or microscopic solid lesions are thought to precede tumor formation. In 2024, the International Society of Urological Pathology (ISUP) held a consensus meeting on precursor lesions of urologic neoplasms in Florence, Italy. This report details the findings of Working Group 3-Precursor Lesions of the Kidney. Papillary adenoma is likely the best-established precursor lesion in the kidney, thought to be an incipient form of papillary renal cell carcinoma (RCC) with shared morphology, immunohistochemistry, and genetics. Likewise, in patients with VHL disease, the kidney often contains multiple small nodules of clear cells and/or cysts lined by one or more layers of clear cells, likely representing early tumor or precursor lesions. Interestingly, a precursor counterpart for clear cell RCC in the sporadic setting is not well established. In other scenarios, cysts are considered potential precursors of neoplasia, such as those in acquired cystic kidney disease (ACKD) and possibly in some hereditary renal tumor syndromes. The consensus panel proposes the following terms "cyst with epithelial proliferation" for tufted/hyperplastic/cribriform cyst lining in ACKD without solid tumor, and "papillary hyperplasia" for tufting of cyst lining in autosomal dominant polycystic kidney. Terms such as "tumorlet," "microtumor," or "incipient tumor" are acceptable for incidental unencapsulated microscopic lesions in hereditary syndrome patients. There is insufficient evidence for the diagnosis of "tubular dysplasia" as a precursor to RCC at the present time.

Tubulocystic renal cell carcinoma is a rare renal neoplasm with imaging characteristics that may make it challenging to differentiate from benign cystic lesions. This retrospective single-institution study characterized the multimodality imaging features of pathologically confirmed tubulocystic renal cell carcinoma with emphasis on ultrasound (US) findings. Cases identified between 2016 and 2023 were reviewed for demographic, clinical, and imaging features on computed tomography (CT), magnetic resonance imaging (MRI), and US. Seven patients (6 male, 1 female; mean age 61 ± 8 y) were included, with presentations of abdominal pain (n=2), hematuria (n=1), and incidental detection (n=4). The mean maximal tumor diameter was 2.4 cm (range: 1.4-4.8 cm); 6 lesions were round and 1 was bilobed. On CT, masses demonstrated low attenuation (mean 15 HU) with variable enhancement (mean 23 HU). MRI in 5 cases demonstrated predominantly T1 hypointense and T2 hyperintense lesions, with 1 lesion showing mixed T2 signal intensity; 3 cases showed enhancement, including septa or a mural nodule. Two hyperechoic lesions demonstrated enhancement on MRI, with enhancement corresponding to the hyperechoic portions of the mixed echogenic mass. US in 5 cases showed 3 uniformly hyperechoic, 1 mixed echogenic, and 1 septated hypoechoic mass, all demonstrating posterior acoustic enhancement. CEUS in 1 case revealed septal enhancement. Although CT and MRI features may mimic cysts, US most commonly demonstrates a hyperechoic lesion with posterior acoustic enhancement and may provide important additional diagnostic information when other imaging findings are equivocal.

Autosomal dominant Alport syndrome (ADAS) is the least common form of Alport syndrome, the second most common monogenic cause of chronic kidney disease after autosomal dominant polycystic kidney disease. We report a 14-year follow-up of a patient with ADAS carrying a likely pathogenic heterozygous variant in COL4A3 (Gly366Arg substitution). The disease initially presented with microhematuria and no renal impairment on analysis or ultrasound. The patient progressively developed bilateral renal cysts and renal failure -a classic renal pattern of the syndrome- and bilateral hearing loss. Incidentally, infertility study (had not children) showed teratozoospermia and elevated levels of luteinizing hormone and progesterone, hormones associated with spermatogenesis. Long-term follow-up of rare variants of Alport syndrome helps refine genotype-phenotype correlations and disease progression. The incidental finding of teratozoospermia raises the possibility of an etiological association, that warrants further investigation as a3(IV) collagen chains involved in spermatogenesis are present in seminiferous tubules.

Cystic lesions of the kidney represent a heterogeneous group of conditions ranging from non-neoplastic processes to benign and malignant neoplasms. With the widespread use of cross-sectional imaging, these lesions are detected with increasing frequency, often incidentally during radiologic evaluation. The Bosniak classification system remains the primary radiologic framework for estimating malignancy risk and guiding management decisions for cystic renal masses. However, imaging findings alone are frequently insufficient for definitive diagnosis, and accurate classification often requires integration with gross and histopathologic evaluation. In this review, we provide an integrated overview of cystic renal lesions with emphasis on their clinical, radiologic, gross, histopathologic, and immunohistochemical characteristics. The spectrum includes non-neoplastic entities to benign and malignant neoplasms. In addition, tumors that are typically solid but may demonstrate prominent cystic change are discussed, highlighting the importance of including these entities in the differential diagnosis when evaluating complex cystic renal masses. Understanding the morphologic spectrum and recognizing key diagnostic features are essential for distinguishing benign cysts from cystic neoplasms and for avoiding both underdiagnosis and overtreatment. Radiologic-pathologic correlation and a structured diagnostic approach are critical for accurate classification and optimal patient management. Continued refinement of imaging criteria and improved multidisciplinary collaboration will further enhance the diagnostic evaluation and clinical management of cystic renal lesions.