**4. Delayed hypocerebral perfusion following aneurysmal clipping surgery: A new clinical entity**

Among 58 cases, we found five individuals who had undergone neurosurgical clipping for subarachnoid hemorrhage either at our facility or in the other hospital. Notably, two out of five cases were found to have hypoperfusion of cerebral blood flow at the distal regions of artery where clipping was performed. A 72‐year‐old female underwent neurosurgical clipping of the right mid‐cerebral artery due to the ruptured aneurysm at the age of 58 at the other hospital (**Figure 2A**). Eleven years after surgery, she presented at our hospital, complaining of right tinnitus, vertigo, and headache. She was eventually evaluated by CT angiography together with CT perfusion, which revealed an apparent hypoperfusion of the right mid‐ cerebral artery (**Figure 2B**). Her cerebral blood flow corresponding to the region where the right mid‐cerebral artery perfuses is 16.4 mL/100 g/min, whereas the cerebral blood flow of the contralateral hemisphere was 32.7 mL/100 g/min. The CBV corresponding to the right mid‐ cerebral artery is 1.0 mL/100 g and the CBV of the contralateral hemisphere was 1.1 mL/100 g.

**Figure 2.** (**A**) A 72‐year‐old female underwent neurosurgical clipping of the right mid‐cerebral artery due to the rup‐ tured aneurysm at the age of 58 at the other hospital. Her CT angiography is shown in the figure. (**B**) CT perfusion findings revealed an apparent decrease of cerebral blood flow perfused by the right mid‐cerebral artery (indicated by the arrows). (**C**) A 63‐year‐old woman underwent emergent neuroclipping surgery for the ruptured anterior‐communi‐ cating artery aneurysm. Her CT angiography is shown in the figure. The surgery is successfully carried out. (**D**) Six months postoperatively, a physiotherapist noticed her slight memory defect, and CT perfusion was evaluated, which revealed an apparent hypoperfusion of both frontal lobes (indicated by the arrows).

The right MTT was 4.6 s and the left MTT was 4.6 s, confirming the results that the cerebral blood flow of the right mid‐cerebral artery just distal of the clipped region is actually decreas‐ ing. Similarly, a 63‐year‐old woman underwent emergent clipping surgery for the ruptured anterior‐communicating artery aneurysm (**Figure 2C**). During the follow‐up period, she had a slight defect of memory, and the CT perfusion was evaluated, which clearly revealed the impairment of cerebral blood flow in both the frontal lobes (**Figure 2D**). The quantification of the cerebral blood flow actually confirmed the decrease of the cerebral blood flow in both the frontal lobes as compared to the regions where mid‐cerebral artery perfuses (CBF; right frontal: 17.1 mL/100 g/min, left frontal: 14.1 mL/100 g/min; right temporal: 43.5 mL/100 g/min, left temporal: 48.4 mL/100 g/min). The significance of the findings is that although anesthesiolo‐ gists usually consider the patients who had successfully undergone neuroclipping surgery as the standard risk group, we found here that they still may pose a risk for neurological complications perioperatively even after the successful surgery. The finding may encompasses not only to the perioperative risks of patients who had undergone aneurysmal clipping surgery but also to its delayed neurological manifestations associated with the hypoperfusion of parental artery, a possible new diagnostic clinical entity.
