Fast imaging employing steady-state acquisition (FIESTA) MRI to investigate cerebrospinal fluid (CSF) within dural reflections of posterior fossa cranial nerves

Abstract

Objective: There is no consensus approach to covering skull base meningeal reflections-and cerebrospinal fluid (CSF) therein-of the posterior fossa cranial nerves (CNs VII-XII) when planning radiotherapy (RT) for medulloblastoma and ependymoma. We sought to determine whether MRI and specifically fast imaging employing steady-state acquisition (FIESTA) sequences can answer this anatomical question and guide RT planning. Methods: 96 posterior fossa FIESTA sequences were reviewed. Following exclusions, measurements were made on the following scans for each foramen respectively (left, right); internal acoustic meatus (IAM) (86, 84), jugular foramen (JF) (83, 85) and hypoglossal canal (HC) (42,45). A protocol describes measurement procedure. Two observers measured distances for five cases and agreement was assessed. One observer measured all the remaining cases. Results: IAM and JF measurement interobserver variability was compared. Mean measurement difference between observers was 20.275 mm (standard deviation 0.557). IAM and JF measurements were normally distributed. Mean IAM distance was 12.2 mm [95% confidence interval (CI) 8.8-15.6]; JF was 7.3 mm (95% CI 4.0-10.6). The HC was difficult to visualize on many images and data followed a bimodal distribution. Conclusion: Dural reflections of posterior fossa CNs are well demonstrated by FIESTA MRI. Measuring CSF extension into these structures is feasible and robust; mean CSF extension into IAM and JF was measured. We plan further work to assess coverage of these structures with photon and proton RT plans. Advances in knowledge: We have described CSF extension beyond the internal table of the skull into the IAM, JF and HC. Oncologists planning RT for patients with medulloblastoma and ependymoma may use these data to guide contouring.

Highly Conformal Craniospinal Radiotherapy Techniques Can Underdose the Cranial Clinical Target Volume if Leptomeningeal Extension through Skull Base Exit Foramina is not Contoured

“…This may slightly reduce the strength of direct plan comparison, but accurately reflects the current clinical dilemma. Published FIESTA MRI data and a previous surgical study prove that dura and CSF are present to the fundus of the IAM [17], [31]. Equally, the risk of sensorineural deafness rises sharply with doses above 40–45 Gy [32], [33].…”

“…Work on the detailed anatomy of the IAM, JF and HC using fast imaging employing steady-state acquisition (FIESTA) magnetic resonance imaging (MRI) has clearly shown CSF beyond the internal table of the skull, which many clinicians would consider to be a CTV surrogate [17] . This study is the first to investigate the dosimetric implications of failure to include leptomeningeal reflections of posterior fossa cranial nerve foramina in the CTV of CSI treatment plans for medulloblastoma.…”

“…Treatment plans, including DICOM imaging files; structure sets and dose cubes were drawn from archive and reloaded into virtual simulation software (PROSOMA 3.3, OSL, Shrewsbury, UK). Using published anatomical data [17] , new contours and target volumes were constructed for each patient. Using bone density windows, a contour was drawn for each individual right and left IAM, JF and HC, to include all possible areas of CSF extension on bone density windows – each volume was drawn and saved as a separate structure; R_IAM, L_IAM, R_JF, L_JF, R_HC, L_HC.…”

“…Field-based CSI protocols recommend a margin of 5 mm below the cribriform plate and at least 10 mm below the skull base elsewhere in order to cover cranial nerve meningeal reflections. Recently published work has shown that cerebrospinal fluid (CSF) and thus surrounding meningeal surfaces may be found over a centimetre beyond the internal table of the skull in the internal acoustic meatus (IAM), jugular foramen (JF) and hypoglossal canal (HC) [17] . This finding may be of interest for clinicians planning radiotherapy for patients with medulloblastoma.…”

Can pulsatile CSF flow across the cerebral aqueduct cause ventriculomegaly? A prospective study of patients with communicating hydrocephalus

“…MRI investigations were carried out on a 3 Tesla scanner (GE Discovery MR 750, Waukesha, WI) with a 32-channel head coil. The structural data for the ventricular system was acquired by a Fast Imaging Employing Steady-state Acquisition Cycled Phases (FIESTA-C) sequence, a sequence with T2/T1 contrast which allows for excellent distinction between fluid-filled spaces and surrounding tissues [20, 21]. The sequence was optimized to achieve the highest structural resolution possible to avoid partial volume effects and to assess the CA geometry as accurately as possible.…”