Evaluating the Monro-Kellie Doctrine: Contralateral Hemisphere Shrinkage in Intracerebral Hemorrhage Patients

Intracerebral hemorrhage (ICH) along with aggravating factors, such as edema, can raise intracranial pressure (ICP) to pathological levels. Diversion of some cerebrospinal fluid (CSF) and venous blood out of the cranium can limit ICP rises while maintaining cerebral perfusion pressure. Brain tissue itself is widely considered immutable in volume but prone to distortion (e.g., midline shift). However, distal brain regions shrink acutely following ICH in rodents. Tissue contraction arises from cell shrinkage and increased packing density. This "tissue compliance" is hypothesized to be an additional mechanism to limit ICP rises. Here, we examined whether and by how much parenchyma volume reduction occurs in ICH patients. We conducted a retrospective analysis on computed tomography (CT) scans of 96 ICH patients (average age 63.8 years old, 55% male) with an average hematoma volume of 32.4 and 35.3 mL at the first and second scan (separated by ~ 23 h), respectively. Hematoma growth (any absolute increase) occurred in 44% of patients, with a minimal but significant growth of the hematoma of 2.9 mL on average across all patients (p = 0.028). As hypothesized, the contralateral hemisphere volume was significantly reduced by 12.7 mL (p < 0.0001) between scans. This was unrelated to midline shift (R² = 0.012, p = 0.21), which averaged 2.3 mm. These findings suggest that distal parenchymal shrinkage may be a major compliance mechanism after ICH; the implications for ICP and brain function merit further study.