Transient Hyperemia Immediately after Rapid Decompression of Chronic Subdural Hematoma

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To the Editor: When we read the article by Ogasawara et al. (5), we had the impression that they did not refer to some concepts regarding intracranial pressure and autoregulation: specifically, the relationship between a chronic state of intracranial hypertension and the vascular adjustment secondary to this phenomenon. How do the authors explain the observation that the asymmetric index values were almost the same before the surgical procedures and 3 days after surgery? In Figure 2 of the article, it is evident that the asymmetric index values were similar during the preoperative and postoperative periods. This means that, in the cortex underlying the hematoma, the cerebral blood flow (CBF) was not decreased in the preoperative period, because autoregulation provided a relatively constant CBF, even in elderly patients. This corresponds to the results of Ishikawa et al. (2) and Tanaka et al. (7), but, of course, it is not in accordance with the hypothesis proposed by Spetzler et al. (6). In my opinion, when a sudden decompression of the intracranial space occurs, regardless of the cause, there is a secondary response of increased CBF, but it is not “local,” as the authors state; if we analyze Figure 3, it is evident that the red-colored areas are more extensive on the contralateral side of the hematoma (observe the center and left images, and compare both contralateral sides to the hematoma). Of course, to evaluate these images, we can use only our visual assessment. The fact that these phenomena are more frequently found in older patients is perfectly consistent with the impairment of acute autoregulation in the elderly (1, 3). In agreement with Muizelaar (4), who has had more than 25 years’ experience with chronic subdural hematoma (CSH), we have had only one patient with intracerebral hematoma after evacuation of a CSH; do the authors think that hyperemia was really the cause of this complication? Raul Andrés Pérez Falero Angeles de Lourdes Cardentey Pereda Ivan Francisco Arenas Rodríguez