Cerebrospinal fluid M staging for medulloblastoma: reappraisal of Chang's M staging based on the CSF flow

Abstract

Tumor seeding is a strong negative prognostic factor for patients with medulloblastoma. Because Chang's M staging is based primarily on CT and myelographic findings and might be contradictory to the direction of normal cerebrospinal fluid (CSF) flow, seeding patterns and appropriate staging of medulloblastoma need to be revisited in patients diagnosed in the MRI era. We retrospectively reviewed the clinical and radiological data of 86 patients with a diagnosis of medulloblastoma who were treated in the MRI era. The presence of seeding in each subarachnoid space compartment and the patterns of seeding were analyzed in correlation with patient survival data. Thirty-four patients had gross seeding on perioperative MRI. Thirty-two patients had seeding in the spinal compartment. Sixteen and 12 patients had seeding in the infratentorial and supratentorial compartments, respectively. There was an apparent hierarchy of seeding (ie, from seeding in the spinal compartment up to the supratentorial compartment). Patients with seeding in the spinal compartment had longer progression-free survival (P = .038) and a tendency toward better overall survival (P = .053) compared with patients with seeding in intracranial compartments. We modified Chang's M staging based on the CSF flow and termed this approach "CSF M staging." CSF M staging for medulloblastoma, in which intracranial seeding occupies a higher rank than spinal seeding, was a better predictor of patient prognosis. This modified staging method may be applied to metastatic staging of brain tumors located in the fourth ventricle.

Fig. 1.

Medulloblastoma seeding in the SAS. (A) Leptomeningeal seeding in the spinal SAS. Nodular enhancement was found along the surface of the spinal cord and at the end of the thecal sac (arrows). (B) Diffuse leptomeningeal seeding in the infratentorial SAS compartment. Nodular and linear enhancement was observed along the tentorial surface of the cerebellum (arrowheads). (C) Extensive leptomeningeal seeding in the supratentorial SAS compartment. Thick leptomeningeal enhancement was observed in the bilateral sylvian fissures (white arrows) and in the interhemispheric fissure (black arrow). Thick enhancement was also found in the quadrigeminal cistern and in the sulci of the superior cerebellar vermis (arrowheads).

Fig. 2.

Patterns of seeding in medulloblastoma. Red represents the presence of seeding in the corresponding compartment of SAS. Green represents the absence of seeding in the corresponding compartment. White represents a lack of evaluation for the compartment (ie, no lumbar tapping was undertaken). Each horizontal row corresponds to one patient. Numbers were consecutively attributed to patients who were positive for seeding in each compartment.

Fig. 3.

Kaplan–Meier survival plots for PFS and OS according to the status of seeding at presentation. There were significant differences in PFS and OS between patients without seeding (M0 stage) and patients with seeding (M1–3 stages; P < .001 and P < .001, log-rank test).

Fig. 4.

Kaplan–Meier survival plots according to the seeding patterns. SP group: patients with seeding only in the spinal compartment (n = 16); IT group: patients with seeding in the infratentorial compartment but not in the supratentorial compartment (n = 6); ST group: patients with seeding in the supratentorial compartment (n = 12); IC group: patients with seeding in the intracranial compartment (ST group + IT group; n = 18). There was no difference in survival between the IT and ST groups. Compared with the IC group, the SP group had PFS (A) that was significantly longer (P= .038, log-rank test) and OS (B) that was longer but did not quite reach significance (P= .053, log-rank test).

Fig. 5.

Kaplan–Meier survival plots for PFS (A) and OS (B) according to the CSF M staging, which was modified from Chang's M staging based on the CSF flow.