Phase-contrast cerebrospinal fluid flow magnetic resonance imaging in qualitative evaluation of patency of CSF flow pathways prior to infusion of chemotherapeutic and other agents into the fourth ventricle.

PURPOSE: Nuclear medicine studies have previously been utilized to assess for blockage of cerebrospinal fluid (CSF) flow prior to intraventricular chemotherapy infusions. To assess CSF flow without nuclear medicine studies, we obtained cine phase-contrast MRI sequences that assess CSF flow from the fourth ventricle down to the sacrum. METHODS: In three clinical trials, 18 patients with recurrent malignant posterior fossa tumors underwent implantation of a ventricular access device (VAD) into the fourth ventricle, either with or without simultaneous tumor resection. Prior to infusing therapeutic agents into the VAD, cine MRI phase-contrast CSF flow sequences of the brain and total spine were performed. Velocity encoding (VENC) of 5 and 10 cm/s was used to confirm CSF flow from the fourth ventricular outlets to the cervical, thoracic, and lumbar spine. Qualitative CSF flow was characterized by neuroradiologists as present or absent. RESULTS: All 18 patients demonstrated CSF flow from the outlets of the fourth ventricle down to the sacrum with no evidence of obstruction. One of these patients, after disease progression, subsequently showed obstruction of CSF flow. No patient required a nuclear medicine study to assess CSF flow prior to initiation of infusions. Fourteen patients have received infusions to date, and none has had neurological toxicity. CONCLUSIONS: CSF flow including the fourth ventricle and the total spine can be assessed noninvasively with phase-contrast MRI sequences. Advantages over nuclear medicine studies include avoiding both an invasive procedure and radiation exposure.

MR-derived cerebral spinal fluid hydrodynamics as a marker and a risk factor for intracranial hypertension in astronauts exposed to microgravity.

PURPOSE: To quantify the change in cerebral spinal fluid (CSF) production rate and maximum systolic velocity in astronauts before and after exposure to microgravity and identify any physiologic trend and/or risk factor related to intracranial hypertension. MATERIALS AND METHODS: Following Institutional Review Board (IRB) approval, with waiver of informed consent, a retrospective review of 27 astronauts imaged at 3T was done. Qualitative analysis was performed on T2 -weighted axial images through the orbits for degree of flattening of the posterior globe according to the following grades: 0 = none, 1 = mild, 2 = moderate, and 3 = severe. One grade level change postflight was considered significant for exposure to intracranial hypertension. CSF production rate and maximum systolic velocity was calculated from cine phase-contrast magnetic resonance imaging and compared to seven healthy controls. RESULTS: Fourteen astronauts were studied. The preflight CSF production rate in astronauts was similar to controls (P = 0.83). Six astronauts with significant posterior globe flattening demonstrated a 70% increase in CSF production rate postflight compared to baseline (P = 0.01). There was a significant increase in CSF maximum systolic velocity in the subgroup without posterior globe flattening (P = 0.01). CONCLUSION: The increased postflight CSF production rate in astronauts with positive flattening is compatible with the hypothesis of microgravity-induced intracranial hypertension inferring downregulation in CSF production in microgravity that is upregulated upon return to normal gravity. Increased postflight CSF maximum systolic velocity in astronauts with negative flattening suggests increased craniospinal compliance and a potential negative risk factor to microgravity-induced intracranial hypertension.

Postnatal dexamethasone therapy and cerebral tissue volumes in extremely low birth weight infants.

OBJECTIVE: Our goal was to relate postnatal dexamethasone therapy in extremely low birth weight infants (birth weight of < or = 1000 g) to their total and regional brain volumes, as measured by volumetric MRI performed at term-equivalent age. METHODS: Among 53 extremely low birth weight infants discharged between June 1 and December 31, 2003, 41 had high-quality MRI studies; 30 of those infants had not received postnatal steroid treatment and 11 had received dexamethasone, all after postnatal age of 28 days, for a mean duration of 6.8 days and a mean cumulative dose of 2.8 mg/kg. Anatomic brain MRI scans obtained at 39.5 weeks (mean) postmenstrual age were segmented by using semiautomated and manual, pretested, scoring algorithms to generate three-dimensional cerebral component volumes. Volumes were adjusted according to postmenstrual age at MRI. RESULTS: After controlling for postmenstrual age at MRI, we observed a 10.2% smaller total cerebral tissue volume in the dexamethasone-treated group, compared with the untreated group. Cortical tissue volume was 8.7% smaller in the treated infants, compared with untreated infants. Regional volume analysis revealed a 20.6% smaller cerebellum and a 19.9% reduction in subcortical gray matter in the dexamethasone-treated infants, compared with untreated infants. In a series of regression analyses, the reductions in total cerebral tissue, subcortical gray matter, and cerebellar volumes associated with dexamethasone administration remained significant after controlling not only for postmenstrual age but also for bronchopulmonary dysplasia and birth weight. CONCLUSIONS: We identified smaller total and regional cerebral tissue volumes in extremely low birth weight infants treated with relatively conservative regimens of dexamethasone. These volume deficits may be the structural antecedents of neuromotor and cognitive abnormalities reported after postnatal dexamethasone treatment.