**5. Computed tomography perfusion as the means to noninvasively measure tumor malignancy**

Tumors usually exhibit increased angiogenic activity and neovascularization, which result in increased blood volume. Accordingly, previous studies suggested that CBV and CBF were elevated in tumors, and they may be efficacious in the assessment of tumor angiogenic activity.

A 59‐year‐old male visited our hospital complaining of dizziness and nausea. His T2‐weighed magnetic resonance image showed an overt edematous left temporal lobe (**Figure 3A**). Based on the images obtained, the presence of limbic encephalitis was suspected. He was coinciden‐ tally seropositive for human T‐cell leukemia virus‐1 (HTLV‐1). Accordingly, the other differ‐ ential diagnosis such as non‐Hodgkin lymphoma, limbic encephalitis associated with autoimmunity, paraneoplastic syndrome (PNLE; paraneoplastic limbic encephalitis), herpes encephalitis, and astrocytoma could also be possible. In an attempt to obtain further clues for the diagnosis of his disease, especially to determine whether or not directly to obtain histopa‐ thological findings by craniotomy, CT perfusion study was performed. The CT perfusion findings indicated a moderate increase of CBV in the corresponding region (**Figure 3B**), an apparent increase of TTP (time to peak) (**Figure 3B**), a slight increase of MTT, and an intact CBF (**Figure 3B**), which indicates the potential possibility of the presence of the primary tumor surrounded by the edematous normal brain tissue. Based on the findings, he underwent computer‐navigated craniotomy. The postoperative histopathological findings confirmed the presence of astrocytoma grade 2.

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

revealed an apparent hypoperfusion of both frontal lobes (indicated by the arrows).

124 Current Topics in Anesthesiology

**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

parental artery, a possible new diagnostic clinical entity.

**Figure 3.** (**A**) T2‐weighed magnetic resonance image of a 59‐year‐old male who presented to our hospital because of dizziness and nausea. An edematous region of the temporal lobe is apparent, suggesting the presence of limbic ence‐ phalitis. (**B**) A CT perfusion imaging of the same patient. From left to the right, CBF, CBV, MTT, and TTP are visual‐ ized. The corresponding region where limbic encephalitis is suspected, an apparent increase of CBV and TTP is observed. CBF remained intact and a slight increase of MTT is also observed.

Since an increase of CBV and TTP reflects angiogenic activity and neovascularization of the tumor, our findings may indicate that CT perfusion findings may potentially be predictive of pathologic grade of the tumor and correlate with tumor mitotic activity. Because the diagnosis of limbic encephalitis is extremely difficult and the laboratory investigations often only provide inconclusive evidence, we suggest that CT perfusion is potentially an important modality that may provide clues to the correct diagnosis.
