Abstract
Organized hematoma, which exhibits a net-like appearance on imaging studies, is one of the predisposing factors for the recurrence of chronic subdural hematoma. Patients who are positive for the net-like appearance are often treated with only burr hole surgery. We investigated the relationship between postoperative structural changes in the net-like appearance and the recurrence rate of chronic subdural hematoma. Of the 949 patients with chronic subdural hematoma treated with primary burr hole surgery between January 2010 and April 2021 at our hospital, 268 who were considered positive for the net-like appearance on T2- and T2 star-weighted magnetic resonance images were extracted. We followed the structural changes in the net-like appearance postoperatively and subsequently classified the patients into three groups: decreasing type, shifting type, and no change and deterioration type. The relationship between each structural change and the recurrence rate in the three groups was investigated. Postoperative recurrence requiring surgery occurred in 3.5% of the subjects with decreasing type, 0% with shifting type, and 100% with deterioration type of the net-like appearance (P < 0.05), indicating differences in the recurrence rates according to postoperative structural changes in the magnetic resonance images (MRI) features of chronic subdural hematoma. Our results indicate that the risk of postoperative chronic subdural hematoma recurrence can be predicted by focusing on the structural changes in the postoperative net-like appearance on MRI.
Keywords: chronic subdural hematoma, net-like appearance, magnetic resonance imaging, recurrence
Introduction
Chronic subdural hematoma (CSDH) is one of the most common neurological diseases, of which the risk factors for recurrence include age, alcoholism, diabetes mellitus, hypertension, use of anticoagulants, arachnoid cysts, and organized hematoma.1-5) Various imaging features have been suggested to be useful in the diagnosis of organized hematoma preoperatively, one of which is a net-like appearance on cranial magnetic resonance images (MRI),6-11) representing multifocal hematoma with multiple septae.
The presence of a net-like appearance in CSDH is believed to indicate an organized hematoma, which is associated with the likelihood of frequent recurrence. However, we frequently experience cases of CSDH with a net-like appearance that are cured after only a single burr hole drainage. To the best of our knowledge, there are no reports on the structural characteristics of lesions with a net-like MRI appearance that were successfully treated. To elucidate the association between the recurrence rate of CSDH in cases with a net-like appearance on cranial MRI and structural changes in the net-like appearance after treatment, we postoperatively followed changes in the net-like appearance on MRI and examined the correlation between these structural changes and the recurrence rate of CSDH with a net-like appearance.
Materials and Methods
Study design
This study was approved by the ethics committee of Nakamura Memorial Hospital (Approval No. 2022032901) and was conducted in accordance with the principles of the Declaration of Helsinki. The participants in this observational, non-randomized study were identified via a retrospective electronic chart review of patients with CSDH surgically treated at the Nakamura Memorial Hospital between January 2010 and April 2021. According to our institutional protocol, all patients in this study underwent burr hole surgery. Informed consent was obtained from all patients prior to treatment.
Patients
We identified 949 patients with CSDH who underwent burr hole surgery during the observation period. Among them, patients who presented a net-like appearance on T2- and T2 star-weighted MRI were extracted, excluding those with neither CT nor MRI images on the preoperative day and 7 days after surgical treatment.
Surgical methods
Surgery is usually performed under local anesthesia. The patient's head is rotated approximately 15° from the side of the hematoma (if bilateral, the patient's head is fixed in the midline position, and the following technique is performed bilaterally). A single burr hole is drilled at a site located 6.0 cm lateral and 3.0 cm anterior to the bregma, and a single drain is inserted from the frontal direction to the deepest part of the hematoma cavity. The distance from the lamina externa to the deepest point is about 6.5 cm. To prevent hematoma-air communication, the wound is closed. The hematoma cavity is then irrigated copiously with ARTCEREB (irrigation and perfusion solution for cerebrospinal surgery) until the drainage is clear. Patients are kept strictly on bed rest until the first postoperative day. The drain is set at an external pressure of 0-cm H2O, and a CT scan is performed on postoperative day 1, after which the drain is removed.
Imaging
According to our hospital imaging protocol, patients with suspected CSDH undergo CT and MRI as soon as they present to our hospital, and follow-up CT and MRI are performed 7 days after surgery. We consider a hematoma with a net-like appearance as indicating the presence of several septations that have divided the hematoma into more than 10 compartments visible on preoperative T2- and T2 star-weighted images. In this study, we followed postoperative structural changes in the net-like appearance on MRI, based on which the patients were classified into three groups: decreasing type (group A), shifting type (group B), and no change and deterioration type (group C). Fig. 1 presents each type of postoperative change in the net-like appearance. Briefly, in group A, struts of the net-like appearance decreased, but the overall structure of the preoperative net-like appearance remained. In group B (shifting type), there was involution of the entire structure of the net-like appearance and lateral shift of the entire hematoma cavity. In the no change and deterioration type (Group C) group, there were no structural changes in and increasing struts of the net-like appearance, although the entire hematoma cavity was reduced. All the images were analyzed by two experienced stroke neurologists.
Fig. 1.
Four types of postoperative changes in the net-like appearance on magnetic resonance imaging.
In the decreasing type pattern, struts of the net-like appearance decreased, but the overall structure of the preoperative net-like appearance remained. In the shifting type, there was involution of the entire structure of the net-like appearance and lateral shift of the entire hematoma cavity. In the no change and deterioration types, there was no structural change in the net-like appearance or increase in the struts of the net-like appearance, although the entire hematoma cavity is reduced.
Clinical and statistical analysis
The three groups were compared for the primary outcome of the reoperation rate in each group. Categorical variables were analyzed using the chi-squared test, whereas continuous variables were analyzed via analysis of variance. Statistical significance was set at P < 0.05. All statistical analyses were conducted using SPSS version 23.0 (IBM, Armonk, NY, USA).
Results
Clinical information
A total of 949 patients with CSDH underwent burr hole surgery during the study period. Among them, 314 (33.1%) had unilateral CSDH with a net-like appearance, 268 of whom were analyzed after excluding 46 due to lack of follow-up MRI data. Table 1 presents the general characteristics of the groups. Age, sex, baseline clinical risk factors, and medication history of Goreisan did not differ between the three groups, except for the incidence of hypertension and diabetes mellitus.
Table 1.
Baseline characteristics of the study groups
| Baseline characteristics | Group A (n = 142) |
Group B (n = 111) |
Group C (n = 15) |
P value |
|---|---|---|---|---|
| Age, years (mean ± SD) | 75.0 ± 12.3 | 76.9 ± 11.5 | 76.3 ± 8.9 | 0.426 |
| Male, n (%) | 84 (59.2) | 66 (59.5) | 12 (80.0) | 0.424 |
| Risk factors, n (%) | ||||
| Hypertension | 42 (29.6) | 27 (24.3) | 10 (66.7) | p < 0.05 |
| Diabetes mellitus | 17 (12.0) | 16 (14.4) | 8 (53.3) | p < 0.05 |
| Previous stroke | 21 (14.8) | 15 (13.5) | 2 (13.3) | 0.957 |
| Antithrombotic therapy | 20 (14.1) | 20 (18.0) | 3 (20.0) | 0.791 |
| Renal failure | 8 (5.6) | 4 (3.6) | 1 (6.7) | 0.867 |
| Tumor | 22 (15.5) | 21 (18.9) | 3 (20.0) | 0.857 |
| Preoperative use of goreisan | 14 (9.9) | 13 (11.7) | 1 (6.7) | 0.956 |
| Duration of preoperative use of goreisan, days (mean ± SD) | 3.58 ± 14.7 | 7.31 ± 47.7 | 8.6 ± 33.3 | 0.636 |
| Postoperative use of goreisan | 110 (77.5) | 82 (73.9) | 11 (73.3) | 0.872 |
Baseline clinical risk factors did not differ between the three groups, except for hypertension and diabetes mellitus. SD, standard deviation.
Primary outcome measures
Of the 268 patients, 20 required reoperation after the first burr hole surgery, indicating an overall first-time cure rate for CSDH with a net-like appearance of 92.5%.
The patients who required reoperation included five (3.5%) in group A, none (0.0%) in group B, and all (100%) in group C (Table 2), indicating significant differences between the three groups (P < 0.05) in the reoperation rates.
Table 2.
Primary outcomes of this study
| Outcomes | Group A
(n =142) |
Group B
(n =111) |
Group C
(n =15) |
P value |
|---|---|---|---|---|
| Cure | 137 | 111 | 0 | <0.05 |
| Reoperation | 5 | 0 | 15 | <0.05 |
Significant differences were observed between the three groups (P < 0.05) as evaluated using chi-squared test.
Postoperative course after the first burr hole surgery
Follow-up CT failed to identify any differences between the imaging features in the three groups (Fig. 2).
Fig. 2.
Comparison of CT images in each group.
The volume of the postoperative hematoma cavity was reduced in all groups, although CT could not identify any differences in the appearance of the hematoma structure between them.
Table 3 presents the treatment course for each group. In group A, the average interval from the first operation to reoperation was 14.4 days. Four of the five patients underwent follow-up MRI on day 7 after reoperation, and all were cured after the second burr hole surgery. Among the patients, one showed a decrease in the net-like appearance after reoperation and was cured, and the remaining three patients exhibited a shifting type pattern and were healed.
Table 3.
Treatment course of chronic subdural hematoma with net like appearance
In group C, the average interval between the first and second surgeries was 11.8 days. Among the 15 patients, 8 had deterioration, 6 demonstrated change in the pattern, and 1 had tube obstruction immediately after the first surgery.
Of the eight patients in group C who demonstrated a deterioration pattern after the second burr hole surgery, seven underwent MRI follow-up on the day 7 after reoperation. Of them, five showed a decreasing pattern after reoperation, one of whom had hematoma recurrence and required craniotomy to remove the hematoma. MRI after the second surgery revealed a shifting pattern in the sixth patient, indicating cure, whereas the remaining patient showed no change in the structure of the residual net-like appearance after the second surgery and symptomatic regrowth 4 years later. Based on the imaging findings and clinical course, the patient was judged to have a highly organized hematoma, for which craniotomy was performed, resulting in a cure.
Of the six patients with an unchanged pattern after the second burr hole surgery, four underwent MRI follow-up on day 7 after reoperation. Two patients exhibited a decreasing pattern after reoperation and were cured. The remaining two patients showed no change after reoperation, and one of them required craniotomy for hematoma removal. The other patient was treated conservatively because there were no obvious postoperative symptoms and strong suspicion of the presence of an organized hematoma at the time of the second burr hole surgery.
Discussion
CSDH although we often encounter patients with a positive net-like appearance treated with only burr hole surgery. The results of this study, which evaluated the recurrence rate of CSDH in patients that preoperatively presented a net-like appearance on cranial MRI, confirmed the presence of a correlation between structural changes in the net-like appearance following surgery and CSDH recurrence.
Several reports have evaluated CSDH with a net-like imaging appearance, and there are several reports of highly organized cases.7-11) Most of them reported a low cure rate with burr hole surgery, and primary craniotomy was the main surgical strategy adopted. In our cohort of 314 patients with CSDH, 92.5% of those who presented with a net-like appearance were successfully treated with only one burr hole surgery, which is equal to or lower than the previously reported initial cure rates of 80%-97% after burr hole surgery.12-14) In this study, CT performed 7 days after surgery revealed no differences between the three groups of this study (Fig. 2), although differences in the structural changes were observed on MRI. Therefore, we believe that MRI evaluation should be preferentially performed both preoperatively and postoperatively to identify the structural changes that might be useful for the identification of CSDH patients who present a net-like appearance and are at a high risk for recurrence.
Fujisawa et al.15) demonstrated that mixed-intensity CSDH that required septation was significantly thicker than other hematomas and that the intrahematoma components showed significantly higher values of hemolysis-related parameters associated with the chronic phase of hematomas. Chronic-stage hematomas with multiple septae (net-like appearance in this study) are often stable with scant neovascularization. Therefore, patients in whom the structure of the hematoma cavity tends to regress, as in groups A and B, are expected to be cured without hematoma recurrence after the first burr hole surgery. On the other hand, Group C included patients with slight structural change or worsening of the net-like appearance. Once the hematoma volume is reduced by drainage, there is slight structural change in the internal struts and slight subsequent regression, which might necessitate reoperation due to the lack of symptomatic improvement. It is also possible that some of the patients with increased struts might have been reactivated within the hematoma by burr hole surgery, contributing to further angiogenesis, although this remains to be investigated further. Based on the results of this study, we recommend the following treatment options in patients with CSDH. The initial treatment method should be burr hole surgery, as suggested by the high cure rate after the initial burr hole surgery in our CSDH cases with a net-like appearance. If the net-like appearance is seen to decrease or shift on MRI performed on postoperative day 7, the patient should be followed up the same as with usual CSDH. However, if the net-like appearance remains unchanged or worsens on MRI performed on postoperative day 7, our results indicate that a recurrence rate of 100% can be expected, and the patient is likely to require reoperation within an average interval of less than 2 weeks, and such patients, thus, require more careful follow-up. The recurrent cases treated with second burr hole surgery were found to heal with similar imaging changes. Therefore, burr hole surgery is recommended as the treatment of choice in CSDH cases requiring reoperation, and craniotomy should be reserved for the third and subsequent surgeries on a case-by-case basis.
Conclusion
In CSDH with a net-like appearance on cranial MRI, the risk of postoperative recurrence can be predicted by confirming structural changes between the pre- and postoperative net-like appearance on MRI.
Conflicts of Interest Disclosure
This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Furthermore, none of the authors have any commercial or financial involvement in connection with this study that represents or appears to represent any conflicts of interest.
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