Value of diffusion weighted magnetic resonance imaging in lesion characterization of head and neck lesions

Head and neck masses are seen at all age groups while being presented in a wide range of spectrum. A variety of imaging techniques can help in characterization of head and neck masses including ultrasonography (US), computed tomography (CT) and magnetic resonance imaging (MRI). Biopsy is commonly used, but it is invasive and may give false results (1). Diffusion weighted MR imaging (DWI) is a technique for the visualization of microscopic water diffusion, the random motion of water molecules, in tissues (2). The extent of translational diffusion of molecules measured in the human body is referred to as the apparent diffusion coefficient (ADC). ADC values express the rate of diffusional motion and they can be obtained by calculating and measuring signal intensity in a series of diffusion weighted MR images. ADCs are expected to vary according to the microstructures of tissues or pathophysiologic states that are intrinsic to different tissues (3). ADC values are different between benign and malignant neck pathologies, as for malignant lesions show low ADCs while benign lesions show high values (4). The purpose of our study is to show the contribution of DWI to sensitivity in characterization of head and neck masses together with histopathologic correlation, to determine the difference in ADC values using DWI in order to distinguish malignant and benign head and neck lesions, lymphoma and carcinoma, and malignant lymph nodes and benign lymph nodes, and to determine cut-off values for these distinctions. In our study 88 patients (95 lesions) that were presented with neck lump in our hospital, referred to radiology department after physical examination with initial diagnosis of neck mass and gone through neck MRI, whose final diagnosis were made by biopsy and/or by using imaging techniques such as MRI, anjiography and whose ages change between 3 months to 86 years were included. Patients who had gone through neck diffusion MRI in Radiology Department of Başkent University Hospital between the dates March 2010 to October 2011 and January 2012 to May 2012 were searched retrospectively. The patients were divided into five groups including lymphoma, carcinoma, other malignant masses excluding lymphoma and carcinoma, benign solid masses and benign cystic masses. The contrast-enhanced neck MRI examinations of patients were performed on two 1,5- iv Tesla (T) MR systems. Besides, before the contrast agent administration, diffusion-weighted MR imaging was performed by using EPI technique, acquired with b values of 0, 400 and 800 sec/mm2 on transverse plane and ADC maps were constructed. ADC values were measured on ADC maps by drawing ROI (region of interest) on the lesion which was determined with DWI. The statistical differences of ADC values between the groups were evaluated using "Kruskal-Wallis Test". In literature, it is indicated that malignant head and neck masses show restricted diffusion and in cases of lymphoma this restriction is even more evident, whereas in benign lesions this restriction decreases as the lesion progresses to a cystic inner structure, yet more, elevated diffusion is observed. When compared to benign lesions, in malignant lesions low ADC values are obtained and in lymphomas even lower values are obtained compared to the other malignant neck masses (The ADC values are 1.56±0.51 x 10ˉ3 mm2/sn, 0.66±0.17 x 10ˉ3 mm2/sn and 1.13±0.43 x 10ˉ3 mm2/sn in benign lesions, lymphomas and malignant neck masses excluding lymphomas, respectively) (3). In this study, we aimed to determine the efficiency and sensitivity of ADC values measured in diffusion MRI study to distinguish malignant and benign masses, lymphoma and carcinoma, and malignant lymph nodes and benign lymph nodes, for the characterization of head and neck masses.