Partial Nephrectomy for a Bosniak Category IV Cyst Revealing Multilocular Cystic Renal Neoplasm of Low Malignant Potential

Multilocular cystic renal neoplasm of low malignant potential (MCRNLMP) is a rare subtype of clear cell renal cell carcinoma (CCRCC), constituting approximately 2-4% of CCRCC cases. Formerly classified as multilocular cystic renal cell carcinoma (MCRCC), it was redefined by the World Health Organization (WHO 2016) and the International Society of Urological Pathology (ISUP 2013) due to its distinct pathological features and lack of metastatic potential. MCRNLMP is characterized by cysts encapsulated by fibrous tissue lined by clear cells with low nuclear grade, without expansile nodules or invasive growth. These features and specific immunohistochemical markers distinguish it from other cystic renal tumors and underscore its favourable prognosis.

The case of a 46-year-old male who exhibited dull loin pain and was subsequently diagnosed with a Bosniak category IV renal cystic mass on imaging was presented. A laparoscopic partial nephrectomy was performed, and histopathology confirmed MCRNLMP. The patient's postoperative course was uneventful, and a three-year follow-up showed no evidence of recurrence or metastasis.

In reviewing the literature, it was found that MCRNLMP is associated with a benign clinical course, with neither recurrence nor metastasis reported in patients with adequate follow-up. It remains difficult to differentiate this entity radiologically from other cystic renal masses, necessitating histopathological evaluation for definitive diagnosis. Urologists should recognize MCRNLMP to avoid over-treatment and reduce anxiety for patients. With complete resection, prolonged disease-free survival can be expected, supporting the adoption of longer intervals for follow-up and reduced imaging. This case and literature review highlight the importance of precise histological criteria to identify and manage MCRNLMP effectively.