Preoperative Functional Findings And Surgical Outcomes In Patients With Motor Area Arteriovenous Malformation

BackgroundCase selection for the surgical treatment of arteriovenous malformations(AVMs) of the eloquent motor area remains challenging. Traditionally, we located various functions in different anatomical areas. Surgery may cause permanent functional deficits in patients with lesions involving anatomical eloquent areas. At the last 20 years, researchers found that lesions happened at traditional eloquent areas may induce shift or reorganization of functions. Considering AVMs are congenital lesions, functional reorganization may occur in patients with AVMs involving anatomic eloquent areas. Neurosurgeons may have the chance to resect eloquent area lesions without permanent functional deficits in patients with functional shift or reorganization. Advanced radiological techniques, such as blood oxygen level dependent functional magnetic resonance imaging(BOLD-f MRI) and diffusion tensor imaging(DTI), seem to provide an opportunity to select the surgical patient individually. However, the relationship between preoperative functional findings and surgical outcomes in patients with motor cortical arteriovenous malformations has not been determined. The aim of this study was to determine the risk factors for worsened muscle strength after surgery in patients with this disorder, and the relationship between preoperative functional findings and surgical outcomes in patients with motor cortical AVM. Materials and MethodsFirst, we prospectively studied 48 consecutive patients with AVMs involving motor cortex and/or the descending pathway. All patients had undergone preoperative functional MRI(f MRI) and diffusion tensor imaging(DTI), followed by resection. Both functional and angioarchitectural factors were analyzed with respect to the change in muscle strength. Functional factors included lesion-to-corticospinal tract distance(LCD) on DTI and lesion-to-activation area distance(LAD) and cortical reorganization on f MRI. Based on preoperative muscle strength, the changes in muscle strength at 1 week and 6 months after surgery were defined as short-term and long-term surgical outcomes, respectively.Second, fifteen patients with AVM exactively involving precentral knob and/or paracentral lobule were further studied. Each involved motor function was examined as an independent object. Preoperative functional findings included cortical reorganization, activation around the nidus, corticospinal tract(CST) reorganization, nidus involving the CST and the involved level of CST. The relationship between preoperative functional findings and surgical outcomes was statistically analyzed. A muscle strength≤grade 3 was defined as a poor outcome after surgery, and a muscle strength≥grade 4 was defined as a good outcome.Statistical analysis was performed using the statistical package SPSS(version 20.0.0, IBM Corp.). ResultsTwenty-one patients(43.8%) had worsened muscle strength 1 week after surgery. However, only 10 patients(20.8%) suffered from muscle strength worsening 6 months after surgery. The LCD was significantly correlated with short-term(p < 0.001) and long-term(p < 0.001) surgical outcomes. For long-term outcomes, patients in the 5 mm ≥ LCD > 0 mm(p = 0.009) and LCD > 5 mm(p < 0.001) categories were significantly associated with a lower risk of permanent motor worsening in comparison with patients in the LCD = 0 mm group. No significant difference was(p = 0.116). Nidus size was the other significant predictor of short-term(p = 0.021) and long-term(p = 0.016) outcomes. For long-term outcomes, the area under the ROC curve(AUC) was 0.728, and the cutoff point was 3.6 cm. Spetzler-Martin grade was not associated with short-term surgical outcomes(0.143), although it was correlated with long-term outcomes(0.038).Eighteen objects were created and analyzed. Cortical reorganization(p=1.000) was not correlated with surgical outcomes. However, nidus involving the CST was significantly associated with poor short-term outcomes(1week after surgery)(p=0.028) and permanent muscle strength deficit(p=0.042). Most of the objects had good outcomes(16/18, 88.9%) at 6 months after surgery(long-term outcomes). Only one patient with CST ruptured at the corona radiata level and one patient who suffered from postoperative hemorrhage obtained poor long-term outcomes. Conclusions1. An AVM with a nidus in contact with tracked eloquent fibers(LCD = 0) and having a large size is more likely to be associated with worsened muscle strength after surgery in patients with eloquent motor area AVMs. Surgical treatment in these patients should be carefully considered. In patients with an LCD > 5 mm, radical resection may be considered to eliminate the risk of hemorrhage.2. Nidus involving the CST and the involved level of the CST, rather than cortical reorganization, activation around the nidus, corticospinal tract(CST) reorganization, may be associated with surgical outcomes in patients with motor cortical AVM.