Cerebellocerebral diaschisis is the likely mechanism of postsurgical posterior fossa syndrome in pediatric patients with midline cerebellar tumors

Abstract

Background and purpose: PFS occurs in approximately 25% of pediatric patients receiving surgery for midline posterior fossa tumors. Increasing evidence suggests that PFS represents a complex supratentorial cortical dysfunction related to surgery-induced disruption of critical cerebellocerebral connections. The purpose of this study was to determine whether a consistent surgical damage pattern may be identified in patients with PFS by early postoperative anatomic imaging analysis of the pECP and to test whether DSC can detect corresponding changes in cerebral cortical perfusion to indicate a secondary, remote functional disturbance, which could suggest a diaschisis-like pathomechanism.

Materials and methods: Eleven patients with postoperative PFS were evaluated retrospectively and were paired with age- and sex-matched control subjects in whom PFS did not develop. MR imaging work-up included DSC within 3 to 4 weeks after surgery as well as early postoperative anatomic imaging to evaluate components of the pECP.

Results: DSC showed significant decreases in CBF within frontal regions (P < .05) and a trend to global cerebral cortical hypoperfusion in patients with PFS. Logistic regression analysis suggested a strong (potentially predictive) relationship between bilateral damage to pECP and the development of PFS (P = .04).

Conclusions: Our data suggest that the primary cause of PFS is the bilateral surgical damage to the pECP. This leads to a trans-synaptic cerebral cortical dysfunction (a form of bilateral crossed cerebellocerebral diaschisis), which manifests with DSC-detectable global, but dominantly frontal, cortical hypoperfusion in patients with patients with PFS compared with age- and sex-matched control subjects.

Fig 1.

Example of segmentation of gray and white matter and definition of subvolumes 1 to 8 for section 5 (A). The segmentation map (A) was overlaid on corresponding CBV and CBF parametric maps of patients with PFS and control subjects (image B is a CBF map of a patient with PFS, and image C is that of a matched control subject).

Fig 2.

Axial T2-weighted (A), FLAIR (B), diffusion-weighted (C), and ADC map (D) images demonstrating surgical damage to the upper portion of the left superior cerebellar peduncle (open arrow) and the mesencephalic tegmentum (solid arrow). Diffusion-weighted and ADC map images show restricted water diffusion, consistent with cytotoxic edema. This finding was interpreted as permanent damage to the left superior cerebellar peduncle.

Fig 3.

Coronal T2-weighted (A,B,D) and FLAIR (C) images demonstrating no damage (A), unilateral damage (B,C), and bilateral damage (D) to the superior cerebellar peduncles in 4 different patients. On image B, it is uncertain whether the signal intensity and structural changes (arrow) represent complete damage or correspond to postsurgical edema only (patient did not have PFS). On image C, damage to the right superior cerebellar peduncle (and dentate nucleus) is unequivocal, whereas hypersignal on the left side (arrow) may be interpreted as postsurgical edema (patient had PFS; damaged left dentate nucleus not shown).

Fig 4.

Coronal T2-weighted images in 2 different patients, illustrating unilateral (A) and bilateral (B) damage to the dentate nuclei (arrows).

Fig 5.

Axial (A) and coronal (B) T2-weighted images showing obvious damage to the left superior cerebellar peduncle (solid arrow) and normal right superior cerebellar peduncle (open arrow). The dentate nuclei were more challenging to assess. Damage to the left side (solid arrow) was considered definite, whereas damage on the right side (open arrow) was considered partial. This was a patient who was believed to have only unilateral damage to the proximal ECP on the basis of anatomic damage analysis, but still went on to have PFS clinically, suggesting that the actual lesion involvement of the dentate nuclei was bilateral.