A volumetric prediction model for postoperative cyst shrinkage

OBJECTIVES: With only limited information available on dimensional changes after jaw cyst surgery, postoperative cyst shrinkage remains largely unpredictable. We aimed to propose a model for volumetric shrinkage based on time elapsed since cyst surgery. MATERIAL AND METHODS: We used data from patients that underwent cyst enucleation or decompression between 2007 and 2017 and had at least three computed tomography (CT) scans per patient. We fitted one simple exponential decay model [V(t) = V(0) · e(−ɑt)] and one model with a patient-specific decay rate [V(k)(t) = V(0) · e(−βt + γkt)]. RESULTS: Based on 108 CT scans from 36 patients (median age at surgery: 45.5 years, IQR: 32.3–55.3, 44% female), our simple exponential decay model is V(t) = V(0) · e(−0.0035t) where V(t) is the residual cyst volume after time t elapsed since surgery, V(0) is the initial cyst volume, and e is the base of the natural logarithm. Considering a patient-specific decay rate, the model is V(k)(t) = V(0) · e(−0.0049t + γkt) where γ(k) is normally distributed, with expectation 0 and standard deviation 0.0041. CONCLUSIONS: Using an exponential regression model, we were able to reliably estimate volumetric shrinkage after jaw cyst surgery. The patient-specific decay rate substantially improved the fit of the model, whereas adding specific covariates as interaction effects to model the decay rate did not provide any significant improvement. CLINICAL RELEVANCE: Estimating postoperative cyst shrinkage is relevant for both treatment planning of jaw cyst surgery as well as evaluating the clinical success of the surgical approach. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00784-021-03907-7.