Differentiating Myelography Contrast from Intraventricular and Subarachnoid Hemorrhage Using Dual-Energy CT of the Head: A Case Report and a Review of Literature.

Single-energy computed tomography (SECT) head is a common diagnostic tool to evaluate for intracranial hemorrhage in emergency settings due to its widespread accessibility and non-invasive nature. However, SECT has densitometric evaluation limitations. For example, hyperdensities on SECT such as blood product and iodine contrast appear similarly. Dual-energy CT (DECT) is a relatively under-utilized imaging modality that has the capability to differentiate between multiple materials. This imaging technique can be extremely useful in identifying materials that are otherwise indistinguishable from standard SECT. The authors present a case of a patient with findings suspicious of intraventricular and subarachnoid hemorrhage on conventional SECT. The suspected hemorrhage was subsequently ruled out utilizing DECT, as iodinated contrast can be subtracted out, yielding an image that can differentiate iodine contrast from blood or other hyperdense material. The authors discuss the underlying physics, potential advantages, and limitations of the DECT.

Ring-Enhancing Progressive Multifocal Leukoencephalopathy Mimicking Glioma in a Presumed Immunocompetent Patient With a History of Multiple Sclerosis: A Case Report and Review of the Literature.

The differential diagnoses of ring-enhancing lesions of the brain parenchyma is broad, but complete ring-enhancing lesions often indicate a neoplastic or infectious process. We present a case of a 70-year-old female with a history of multiple sclerosis (MS) who was not on current disease-modifying therapy (DMT) and was found to have a ring-enhancing lesion that mimicked a high-grade glioma. The patient underwent gross total resection, and histopathologic and molecular analysis revealed a diagnosis of progressive multifocal leukoencephalopathy (PML). A subsequent medical workup on the patient was unrevealing aside from mild lymphopenia. This is a unique case that highlights both an unusual clinical presentation and radiographic appearance of PML. There is a known associated increased risk of PML with the use of some DMTs for MS. However, this case raises the question of the possibility of developing PML years after interferon beta-1a therapy in a patient without overt immunosuppression.