New score developed to predict presence of ‘sticky’ perirenal fat

By Afsaneh Gray, medwireNews Reporter

Researchers have devised an image-based scoring system for predicting the presence of “sticky” fat around the kidney, researchers say.

Such fat, termed adherent perinephric fat (APF), can complicate partial nephrectomy surgery, they note, but using imaging to determine the posterior perinephric fat thickness and perinephric stranding could help clinicians to predict the likelihood of encountering it.

The group prospectively analyzed 100 consecutive robot-assisted partial nephrectomies (RAPNs) performed by one surgeon to determine which factors were predictive of APF, defined as the need for subcapsular renal dissection to isolate the renal tumour for RAPN.

The patients had a median age of 63 years, a median body mass index (BMI) of 28.9 kg/m², and the majority, at 62%, were men.

APF, as defined by the surgeon intraoperatively, was found in 30 of 100 cases.

The researchers found a significantly increased likelihood of APF in male patients and patients with a relatively high BMI (≥25 kg/m²), relatively high posterior or lateral perinephric fat thickness (≥2.0 and ≥2.5 cm, respectively) on imaging, and in those with Type 1 or 2 perirenal fat stranding, defined as a linear area of soft tissue attenuation in the perinephric space.

The two most predictive factors were identified by multivariable analysis as posterior perinephric fat thickness and stranding. These two factors were used to create the Mayo Adhesive Probability (MAP) risk score, ranging from 0 to 5 depending on the extent of posterior perinephric fat thickness and presence of stranding.

APF was observed in 6% of patients with a MAP score of 0, 16% of patients with a score of 1, 31% with a score of 2, 73% with a score of 3 or 4, and 100% of patients with a score of 5.

Writing in European Urology, lead author David Thiel (Mayo Clinic, Jacksonville, Florida, USA) and colleagues comment: “The MAP score is an easy-to-calculate image-based nephrometry scoring system that accurately predicts the probability of encountering troublesome APF during RAPN.”

They add that “it seems likely that preoperative knowledge of hostile APF would be useful to all surgeons attempting surgery on the kidney.”

However, the team warns that, owing to the small sample size and the fact that the score was developed using a data-driven approach, the MAP score will need to be validated in a larger patient cohort.

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