Lymph node assessment by diffusion weighted imaging in cervical cancer

Abstract

The use of node size alone to determine the presence ofmetastatic lymphadenopathy has been shown to be a poordiscriminator in pelvic oncological imaging. Functionalimaging is becoming increasingly important in the evalua-tion of cancer patients because of the limitations ofmorphologic imaging. In patients with uterine cervicalcancer, it is quite important to evaluate the involvement oflymph nodes as lymph nodes metastases are an importantprognostic factor, correlating with survival and modifyingtreatment option [1, 2]. In some institutions, routinelaparoscopic lymphadenectomy is performed to accuratelystage lymphatic extension. Non-invasive preoperativelymph nodes staging seems quite important in patient’smanagement as treatment is heavily influenced according tothe presence or absence of lymph node involvement.Recent imaging strategies, such as diffusion-weightedMR (DW-MR) imaging and positron emission tomographyand computed tomography (PET/CT) have lead to somecontroversies regarding the capability of preoperativeimaging to accurately stage malignant lymphadenopathy.DW-MR imaging is a functional imaging technique whosecontrast derives from the random motion of water mole-cules within tissues. PET/CT imaging contrast derives fromthe metabolic consumption of glucose within tissues.DW-MR sequences are quite relevant and recent imagingtechniques that are used to define disease involvement. Inoncological imaging, DW-MR imaging has been linked tolesion aggressiveness and tumour response, although thebiophysical basis for this is not completely understood. Inour clinical experience with female pelvic cancers, bothbenign and metastatic lymph nodes may appear with highsignal intensity on high b-value images, with correspondinglow apparent diffusion coefficient (ADC) values. The proofof concept behind the paper by Choi at el [1] is that tumourinvolvement changes the diffusion properties of malignantlymph nodes as measured by ADC. The reasons for diffusionrestriction and, therefore, lower ADC values in malignantnodesisprobablyrelatedtoacombinationofhighercellularity,tissue disorganization and increased extracellular space tortu-osity. If correct, lymph node involvement, both early indiagnosis and in the follow-up, could be evaluated withdiffusion-weighted images and the corresponding ADC calcu-lations. If these changes can be used to predict staging andmonitor early cancer treatment response, DW-MR techniqueswill become a considerable benefit for these patients.Choi et al. evaluated, in a node-by-node comparison,the diffusion-weighted ADC calculation and size-basedcriteria on T2-weighted images with PET/CT findings ina large series of patients [1]. The series included 163patients with 339 pelvic lymph nodes with short-axisdiameter >5 mm. The minimum and mean ADC, short-and long-axis diameters, and ratio of long- to short-axisdiameters (L/S ratio) were compared in PET/CT-positiveand -negative lymph nodes. There were 118 (35%)positive nodes in 58 patients. There were statisticallydifferent values in PET/CT-positive and PET/CT-negativegroups in minimum and mean ADCs, short- and long-axisdiameters, and L/S ratio (P<0.05). The best discriminatorwas the minimum ADC, with a larger area-under-the-curve (Az=0.864) than mean ADC (0.836), short-axisdiameter (0.764), long-axis diameter (0.640) and L/S ratio(0.652). The sensitivity and accuracy of the minimumADC (86%, 82%) were also greater than when the meanADC value was used.