Eccentric edema pattern preceding postoperative porencephalic cyst formation in subcortical hemorrhage: A case series and literature review.

BACKGROUND: Postoperative porencephalic cyst formation following subcortical hemorrhage evacuation is an uncommon but clinically significant complication. Early imaging features preceding cyst development remain poorly characterized. CASE DESCRIPTION: We report four adult cases of postoperative expanding porencephalic cysts after subcortical hemorrhage evacuation. In all cases, an asymmetric, non-circumferential distribution of perifocal edema was already observed on admission, before surgical intervention. Although the eccentric edema pattern could be suspected on axial imaging, multiplanar reconstruction in a representative case confirmed its three-dimensional spatial distribution and preferential extension toward the deeper (ventricular) side of the lesion. All cases were subcortical hemorrhages without intraventricular extension. Retrospective review of previously reported adult cases suggested similar, but previously undescribed, imaging features. CONCLUSION: An eccentric edema pattern may represent an early imaging indicator of postoperative cyst formation. This finding may reflect a one-way cerebrospinal fluid recruitment mechanism through a slit-like communication. Recognition of this pattern may help predict postoperative cyst formation and neurological deterioration, thereby guiding clinical management.