Cauda equina syndrome (CES) is an uncommon entity that may be caused by a variety of conditions. It refers to dysfunction of the ventral, dorsal, sacral, and coccygeal nerve roots in the region of the filum terminale. We present a case of a 32-year-old woman with a history of BRCA1-positive metastatic breast cancer who complained of lower extremity muscle weakness increasing over a 2-week period and decreased sensation of the lower extremities accompanied by severe constipation and suspected urinary retention with overflow incontinence. The patient underwent whole-body F-FDG PET/CT and MRI of the spine with and without gadolinium-based contrast.