Background: Atypical meningiomas (CNS WHO grade 2) are biologically heterogeneous, and reliable preoperative imaging correlates of tumor biology remain incompletely defined. This study investigated associations between routinely acquired conventional MRI features and histopathological markers of biological aggressiveness within this tumor grade. Methods: We retrospectively analyzed 90 consecutive patients who underwent surgical resection for histologically defined atypical meningiomas between January 2016 and March 2025. Histopathological specimens were re-reviewed according to the 2021 WHO Classification. Conventional MRI features and apparent diffusion coefficient (ADC) values were evaluated in relation to the Ki-67 labeling index (LI), mitotic count, hypercellularity, spontaneous necrosis, pathological brain invasion, and progesterone receptor expression. Ki-67 LI and ADC were analyzed primarily as continuous variables. A literature-informed Ki-67 threshold of ≥8% was used for secondary categorical analysis, with ≥4% and ≥10% retained as sensitivity analyses. Benjamini–Hochberg false-discovery-rate correction was applied to exploratory categorical comparisons. Results: The median age was 59 years, and 56 patients (62.2%) were female. The median Ki-67 LI was 10% (IQR, 5–15), and the median ADC was 0.78 × 10⁻³ mm²/s (IQR, 0.73–0.88). ADC showed a weak inverse correlation with Ki-67 LI (ρ = −0.255; 95% CI, −0.44 to −0.05; p = 0.015) but was not significantly correlated with mitotic count (ρ = −0.124; p = 0.244). In the adjusted continuous model, the association between ADC and Ki-67 was not statistically significant (Ki-67 ratio per 0.1 × 10⁻³ mm²/s increase in ADC, 0.95; 95% CI, 0.87–1.04; p = 0.264). Similarly, the secondary analysis using Ki-67 ≥ 8% yielded an imprecise association with ADC (OR, 0.865; 95% CI, 0.713–1.002; p = 0.054). Among 96 exploratory categorical comparisons, only the association between radiological and pathological brain invasion remained significant after false-discovery-rate correction (q = 0.003). Conclusions: Conventional MRI features showed weak and largely exploratory associations with histopathological markers of biological aggressiveness in histologically defined atypical meningiomas. Lower ADC was weakly correlated with higher Ki-67 LI, but this association was not robust after adjustment. Radiological brain invasion was strongly associated with pathological brain invasion. These findings should be considered hypothesis-generating and require prospective multicenter validation incorporating standardized imaging, molecular profiling, and clinically relevant outcomes before clinical application.

Background/Objectives: Cauda equina neuroendocrine tumors (CENETs) are rare neuroendocrine tumors that predominantly arise in the cauda equina and filum terminale region. Due to their nonspecific clinical and radiological features, preoperative diagnosis remains challenging, and available data are limited to small case series. Methods: This retrospective single-center study included nine patients who underwent surgical treatment for histopathologically confirmed CENETs between 2014 and 2025. Clinical presentation, radiological findings, surgical management, histopathological features, and postoperative outcomes were analyzed. Results: The mean age was 51.2 years, with a slight male predominance. Pain was the most common presenting symptom (77.8%), followed by radiculopathy and sensory disturbances. All tumors were intradural and extramedullary, predominantly located in the lumbosacral region. Radiologically, all lesions were isointense on T1-weighted imaging and demonstrated predominantly homogeneous contrast enhancement. Vascular imaging features, including flow voids (55.6%), eccentric vessel sign (66.7%), and tadpole sign (44.4%), were frequently observed. Gross total resection was achieved in all patients, with no neurological deterioration or major complications. Over a mean follow-up period of 59.6 months, no tumor recurrence was detected. Conclusions: Cauda equina neuroendocrine tumors are rare but surgically curable tumors with excellent prognosis. Although preoperative diagnosis remains difficult, recognition of characteristic vascular imaging features may improve diagnostic accuracy. Gross total resection remains the cornerstone of treatment, providing durable disease control with minimal morbidity.