Whole-Body Diffusion-Weighted Imaging With Background Body Signal Suppression for Primary Tumor Detection in Patients With Brain Metastases

Diffusion-weighted whole-body imaging with background body signal suppression (DWIBS) is a magnetic resonance imaging (MRI) technique that enables noninvasive, radiation-free whole-body screening. By emphasizing diffusion-restricted regions while suppressing background signals, DWIBS has emerged as a potential alternative or complement to fludeoxyglucose-18 positron emission tomography (FDG-PET), particularly for the detection of primary tumors and metastases. Herein, we report two cases in which DWIBS highlighted suspicious lesions that guided targeted CT and biopsy, leading to the identification of the primary tumor after intracerebral metastasis. The first case involved a man in his 60s who presented with headache and diplopia. Brain MRI revealed clival metastasis, which was diagnosed as squamous cell carcinoma. DWIBS highlighted a focal lesion in the mid-esophagus, which prompted targeted contrast-enhanced CT and subsequent endoscopic biopsy that confirmed esophageal squamous cell carcinoma as the primary site. DWIBS revealed a suspicious lesion in the esophagus, which was later confirmed as an esophageal carcinoma. In the second case, a man in his 50s presented with hemiparesis due to brain metastasis, which was diagnosed as adenocarcinoma. Initial computed tomography and FDG-PET/CT did not localize the primary site; DWIBS subsequently demonstrated a focal diffusion-restricted lesion in the right lung apex, which directed further evaluation and was ultimately consistent with a lung primary. While the initial computed tomography and FDG-PET failed to identify the primary site, DWIBS later detected a lesion in the right lung apex, consistent with lung cancer. These cases illustrate the ability of DWIBS to provide actionable complementary information when FDG-PET is unavailable or yields negative findings. DWIBS, which is accessible, cost-effective, and does not involve radiation exposure, represents a promising imaging modality for oncological practice.