THE NEW 2019 BOSNIAK CLASSIFICATION OF COMPLICATED RENAL CYSTS. RADIOPATHOLOGICAL CORRELATION AND CRITICAL REVIEW.
THE NEW 2019 BOSNIAK CLASSIFICATION OF COMPLICATED RENAL CYSTS. RADIOPATHOLOGICAL CORRELATION AND CRITICAL REVIEW.
Carmen Sebastià, Sergio Jiménez, Héctor Alfambra*, M. Musquera*, Tarek Ajami*, Leo Rodríguez**, R. López**, Carlos Nicolau. Radiology, Urology* and Pathology ** Departments. Hospital Clínic de Barcelona.
The new Bosniak Classification system version 2019 (v2019) stratifies the likelihood of malignancy of cystic renal masses according to morphologic features of masses’ enhancing components on computed tomography (CT) or magnetic resonance imaging (MRI). This new version improves inter-reader agreement between radiologists with more precise definitions of radiological findings than Bosniak classification version 2005 (v2005). Recently a meta-analysis has analyzed the diagnostic performance of Bosniak v2019 classification. This new version demonstrated no difference in diagnostic accuracy between CT and MRI compared to v2005. Also, v2019 has the potential to significantly reduce overtreatment, by downstaging cystic renal masses at the cost of a substantial decline in sensitivity. Bosniak Class I and II cystic masses are benign and do not require follow-up. Class IIF masses have a low but nonzero probability of malignancy and require five years follow-up. Class IIF even if malignant (4-16%) have indolent behavior. Bosniak v2019 compared with previous classification v2005, downgrades previous Bosniak class III, avoiding surgery of benign renal masses. Even though class III has only approximately 50% probabilities of malignancy been surgery still the treatment of choice. Recently active surveillance of class III and even IV renal cysts (90% malignant) has been advocated. The aim of this study is to reevaluate the old classification of Bosniak III and IV cysts based on the new 2019 Bosniak classification and to correlate them with pathological findings, in order to avoid surgery of benign cystic renal masses.
This is a retrospective review of renal masses, classified as Bosniak III and IV cysts, treated with partial nephrectomy between January 2017 and June 2022 in our center. We compare the previous Bosniak classification of these cysts with the reclassification according to Bosniak 2019 criteria by CT correlating with pathological findings. By protocol all patients have a 4 phases CT and contrast enhanced ultrasound (CEUS) Two radiologists have independently reevaluated these complicated renal cysts. In case of discrepancy, consensus has been reached. Clinical, radiological and pathological findings have been recorded.
A total of 56 patients with 57 complicated renal cysts were included in the study. In table 1 there are the characteristics of our sample. Pathologists confirmed malignancy in 43 cystic renal tumors (75%), in which clear cell and papillary renal cell carcinoma (pRCC and ccRCC) were the most usually found (n=41/43, 95%). On the other hand, multilocular renal cystic tumors (recently renamed multilocular cystic renal neoplasm of low malignant potential) (n=8/14, 57%) was the most frequently found cystic mass. Benign cystic renal masses (14) Multilocular cystic nephroma (8) Hemorrhagic benign cysts (2) Abscess (1) Hemangioma (1) Oncocytoma (2) Malignant cystic renal masses (43) Clear cell Renal Cell Carcinoma (ccRCC) (21) Papillary Tenal Cell Carcinoma (pRCC) (20) Chromophobe Renal Cell Carcinoma (1) Metastasis (1) With the reclassification of complicated renal cysts based on Bosniak v2019 criteria, the following results were achieved (Figures 1 and 2): - 21 renal tumors previously considered III or IV Bosniak cysts came to be considered solid tumors since they presented more than 25% of enhancing tissue. 18 of these 21 solid renal tumors turned out to be malignant, the other two correspond to one hemangioma and two oncocytoma that depict more than 25% enhancement in the excretory phase (late enhancement). Tumors with more than 25% enhancement tissue in portal or excretory phase are considered pattern 1 cystic renal masses in our study. - 8 cysts considered Bosniak III, all of which were benign, were reclassified to Bosniak IV because they presented irregular septa or walls thicker than 4mm. All benign renal masses left (after considering hemangioma and oncocytomas solid renal masses) presented only irregular septa and mural wall, no nodules, and two patterns were described: 1- Irregular mural wall with calcifications that appear in hemorrhagic cysts and abscess, considered pattern 3. 2- All the cystic multilocular nephromas presented the same radiological pattern, young patient with a single cyst with multiple septa without nodules, considered pattern 4. - 100% (17) of malignant tumors were considered as Bosniak IV according to the new criteria because all of them presented nodules, two differentiated patterns were found in this sample: - 100% (8) of pRCC presented a papillary pattern (pattern 5) consistent with heterogeneous hypodense mass in all phases with mottled small nodules with even convex or obtuse angles. - 100% (9) of the ccRCC presented hyperenhancing nodules, usually with convex angles, in the arterial phase, consistent with clear cell pattern (pattern 6). - In 8 of the malignant tumors considered Bosniak IV, demonstrated to be solid by contrast enhanced ultrasound (CEUS) (pattern 2). - Only 5 of cystic renal masses considered Bosniak IV by Bosniak v2019 have real cystic content, being mucinous, nonenhancing papillary, necrotic or edematous tumor. - We found calcifications in two haemorragic benign tumors and in two pRCC.
TABLE 1. Demographic characteristics of patients with Bosniak III and IV cystic renal masses. Results are expressed by the mean ± standard deviation for continuous variables, and by the absolute number and percentage for categorical variables.
Figure 1: Comparison between Bosniak version 2005 (v2005) and Bosniak version 2019 (v2019) in our sample. RCC: Renal cell carcinoma. CEUS: Contrast enhanced ultrasound.
Figure 2. Patterns and suggested management of cystic renal masses.
The new Bosniak 2019 classification improves the discrimination between solid renal tumors with cystic changes and real cystic tumors. The incorporation of CEUS also aids in the differentiation between solid and cystic renal tumors. The presence of nodules, and not isolated irregular mural or septal thickening, was the most specific sign of malignancy in the Bosniak IV v2019 cysts. Better differentiation between irregular septa and true nodularity in renal cystic masses considered Bosniak v2019 III or IV must be done. We propose that septa III-IV cysts can be managed with active surveillance and only be treated by surgery nodular III-IV cysts with papillary and clear cell patterns. In this way we can avoid surgery for benign cysts considered III and IV with this new Bosniak v2019, classification.