AJR:198, June 2012 W597 ety of pathology-proven skull tumors, includ- ing lesions of both the skull base and calvar- ia. This information can, in turn, be used to better predict the nature of skull lesions in routine clinical practice and help guide man- agement. The null hypotheses of this study include the following: First, there are no dif- ferences in the ADC values between benign and malignant tumors of the skull; and, sec- ond, there is no correlation between ADC values and cell density in skull tumors. Materials and Methods This study received institutional review board approval and was compliant with HIPAA. The pathology department’s data- base was retrospectively searched for skull base and calvarial lesions. Consecutive cas- es identified between January 2005 and De- cember 2009 with available DWI studies were included in the analysis. All MRI examinations were performed on a 1.5-T clinical scanner. DWI was performed using a 5-mm section thickness with 1-mm spacing, an FOV of 24 cm, and a matrix Diffusion-Weighted Imaging for Differentiating Benign From Malignant Skull Lesions and Correlation With Cell Density Daniel T. Ginat 1 Rajiv Mangla 1 Gabrielle Yeaney 2 Mahlon Johnson 2 Sven Ekholm 1 Ginat DT, Mangla R, Yeaney G, Johnson M, Ekholm S 1 Department of Imaging Sciences, University of Rochester Medical Center, 601 Elmwood Ave, Rochester, NY 14642. Address correspondence to D. T. Ginat (ginatd01@gmail.com). 2 Department of Pathology, University of Rochester Medical Center, Rochester, NY. Neuroradiology/Head฀and฀Neck฀Imaging฀•฀Original฀Research CME This article is available for CME credit. WEB This is a Web exclusive article. AJR 2012; 198:W597–W601 0361–803X/12/1986–W597 © American Roentgen Ray Society D iffusion-weighted imaging (DWI) is routinely applied for evaluating CNS tumors because it provides information about tumor cellular- ity [1]. The presence of densely packed tumor cells inhibits the effective motion of water molecules and therefore results in restricted diffusion [2]. An investigation of astrocyto- mas implanted in an animal model showed that apparent diffusion coefficient (ADC) val- ues inversely correlate with cellularity [3]. Furthermore, significantly higher ADC val- ues have been reported in benign head and neck tumors than in malignant head and neck tumors [4–10]. DWI also plays a role in the evaluation of skull lesions. This modality provides in- creased conspicuity of skull tumors com- pared with conventional MRI sequences [11]. Furthermore, recent studies have shown significant differences in ADCs between be- nign and malignant lesions [4, 5]. The pur- pose of this study was to expand on these prior reports by comprehensively evaluating DWI and histologic features of a wide vari- Keywords: apparent diffusion coef fcient, cell density, diffusion-weighted MRI, skull, tumor  DOI:10.2214/AJR.11.7424 Received June 24, 2011; accepted after revision October 19, 2011. OBJECTIVE. The objective of our study was to determine the utility of diffusion-weight- ed imaging (DWI) and cell density for differentiating benign from malignant skull lesions. MATERIALS฀ AND฀ METHODS. A retrospective review was performed. Minimum ap- parent diffusion coefficient (ADC) values were measured and normalized to white matter, which we refer to as “normalized ADC,” in 24 skull lesions (12 malignant and 12 benign) in 18 patients. In addition, cell densities were measured in 15 cases and correlated with ADC values. RESULTS. The average minimum ADC in malignant tumors was 0.70 × 10 -3 mm 2 /s versus 1.11 × 10 -3 mm 2 /s in benign tumors ( p = 0.0037). Similarly, the average normalized ADC for malignant tumors was 1.03, whereas the average normalized ADC for benign tu- mors was 1.65 ( p = 0.0012). Receiver operating characteristic curve analysis yielded optimal normalized ADC and ADC thresholds of 1.23 (accuracy, 84.6%; sensitivity, 75.0%; specific- ity, 92.3%) and 1.01 × 10 -3 mm 2 /s (accuracy, 83.7%; sensitivity, 83.3%; specificity, 84.6%), respectively. There was a significant inverse correlation between cell density and normalized ADC (r = –0.58; p = 0.023). The low cellularity in chordoma and low-grade chondrosarcoma and high cellularity in eosinophilic granuloma may explain the DWI features of these lesions. CONCLUSION. ADC values in skull lesions correlate with cell density and can poten- tially narrow the differential diagnoses for indeterminate skull lesions. Understanding the histopathologic features of skull lesions can refine interpretation of DWI. Ginat et al. DWI of Skull Lesions Neuroradiology/Head and Neck Imaging Original Research Downloaded from www.ajronline.org by 52.73.204.196 on 05/16/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved