Scintigraphy of Human CSF Flow in Patients with Leptomeningeal Metastasis

Radiopharmaceuticals have the unique advantage of requiring minute physical amounts (<microgram) which are not likely to cause chemical toxicity nor pharmaceutical perturbation of physiology. Intrathecal radiopharmaceuticals allow imaging of physiologic, biochemical, and pathologic processes inside the CSF space which are largely unexplored. The relevant physiology of human cerebrospinal fluid (CSF) flow is outlined. A survey of radiopharmaceuticals used in studying human CSF flow is conducted. Technical details for CSF scintigraphy are briefly discussed. The significance of CSF flow abnormality in patients with leptomeningeal metastasis (LM) and the ability of In-111 DTPA to predict intrathecal pharmacokinetics are reviewed. Whole-body scan schemes provide simplified procedures of CSF scintigraphy, while geometric-mean images allow semi-quantification and derivation of effective half-life (Te) for CSF. These technical advances have been integrated into patient care. Selected results from a retrospective review of CSF flow scintigraphy of patients afflicted with LM are presented with commonly encountered clinical scenarios including CSF block, along with additional studies of Ommaya reservoir malfunction, VP shunt block, and CSF leakage. Radiopharmaceuticals to study LM and to treat LM patients will continue to be important research tools and likely become a mainstay. With advances in nuclear imaging techniques and radiation dosimetry, it may even be feasible to predict potential efficacy.