Introduction
Endoscopic transsphenoidal surgery (ETSS) is a well-established technique in neurosurgery, particularly for the resection of sellar and parasellar tumors such as pituitary neuroendocrine tumors (PitNETs), craniopharyngiomas, meningiomas, and Rathke’s cleft cysts (RCCs). Preoperative assessment for ETSS requires precise evaluation of the tumor location, size, and contrast enhancement, as well as a thorough assessment of surrounding structures, such as cranial nerves and blood vessels. Balanced steady-state free precession (bSSFP) sequences, including constructive interference in steady-state (CISS) and balanced fast field echo (BFFE), provide excellent signal-to-noise ratios and T2-/T1-weighted image contrast1. These sequences are particularly effective for evaluating cranial nerves and cisterns and are considered superior to T2-weighted imaging (T2WI) for these purposes2. Furthermore, the use of gadolinium contrast enhances differentiation between tumors and critical structures, such as cranial nerves and blood vessels, further underscoring the value of contrast-enhanced bSSFP imaging3, 4–5. In particular, for pituitary neuroendocrine tumors (PitNETs), contrast-enhanced bSSFP imaging has also been reported to be useful in depicting the tumor and differentiating it from surrounding anatomical structures6.
Intraoperative MRI (iMRI) offers significant advantages in neurosurgical procedures, particularly in tumor resection. By providing updated imaging information during surgery, iMRI improves tumor removal rates7. In ETSS, the use of iMRI has also been shown to enhance the extent of tumor resection8, 9, 10–11. Its ability to provide updated imaging during surgery enables more precise and complete resections, supporting surgeons in achieving optimal outcomes. The primary goal of ETSS is not only to maximize tumor resection but also to preserve critical anatomical structures, such as cranial nerves. Accurate visualization of these structures with iMRI is therefore crucial to ensuring both the safety and efficacy of the procedure.
iMRI is generally considered to have lower image quality than preoperative or postoperative MRI12; however, this limitation has not been specifically evaluated for intraoperative contrast-enhanced bSSFP. Most patients undergoing ETSS present with visual impairment caused by compression of the optic chiasm by the tumor. The primary goal of treatment in these cases is to relieve this compression. If iMRI can accurately assess the status of the optic chiasm intraoperatively, it would enable timely evaluation of treatment effectiveness during surgery.
This study was performed to evaluate the effectiveness of intraoperative contrast-enhanced bSSFP for visualizing the optic chiasm in patients undergoing ETSS. By comparing contrast-enhanced bSSFP with T2WI, we aimed to determine whether contrast-enhanced bSSFP provides superior visualization during surgery, as observed in preoperative assessments. Furthermore, in cases where intraoperative contrast-enhanced bSSFP visualization deteriorated compared with preoperative imaging, we investigated the factors contributing to this decline. Through this evaluation, we aimed to establish contrast-enhanced bSSFP as a valuable tool for intraoperative use.
Methods
Patients
This study included patients who underwent ETSS between March 2015 and March 2020 with both preoperative and intraoperative MRI, including coronal contrast-enhanced bSSFP and coronal T2WI sequences. We intentionally limited the analysis to ETSS cases because intraoperative factors such as intracranial air and blood in the tumor cavity, which can interfere with optic chiasm visualization, are more commonly encountered in this surgical approach. By focusing on ETSS, we aimed to consistently evaluate the influence of such artifacts on chiasm visibility. At our institution, iMRI was routinely performed for all ETSS cases during the study period. The study was approved by the institutional ethics committee of Kobe University Hospital (No. B200373) and was conducted in accordance with the Declaration of Helsinki and International Council for Harmonisation Good Clinical Practice guidelines. This retrospective study used existing clinical data, and the requirement for individual informed consent was waived in accordance with the ethics committee’s regulations.
Imaging technique
For preoperative contrast-enhanced bSSFP imaging, either contrast-enhanced CISS or contrast-enhanced BFFE was used. CISS imaging was performed on a 3 Tesla MRI scanner (MAGNETOM Skyra; Siemens Healthineers, Erlangen, Germany) following contrast administration, with imaging parameters of TR/TE 6.56/2.66 ms, a 320 matrix, a 160-mm field of view, 0.7-mm-thick slices without gaps, and a 45° flip angle. BFFE imaging was conducted on a separate 3 Tesla MRI system (Achieva; Philips Medical Systems, Amsterdam, The Netherlands) under similar conditions, using parameters of TR/TE 5.2/2.1 ms, a 256 matrix, a 150-mm field of view, 0.7-mm-thick slices without gaps, and a 45° flip angle. Preoperative T2WI was acquired before contrast-enhanced bSSFP imaging, with imaging parameters of TR/TE 3500/96 msec, a 320 matrix, a 200-mm field of view, and 3-mm-thick slices without gaps.
iMRI was performed using the MAGNETOM Skyra with a dedicated 8-channel head coil designed for iMRI (NORAS MRI Products GmbH, Höchberg, Germany). Following T2WI acquisition, a contrast agent was administered, and contrast-enhanced bSSFP imaging was performed. Both T2WI and contrast-enhanced bSSFP during iMRI were acquired using the same imaging parameters as their preoperative counterparts.
Surgical technique
Patients were positioned supine in a fixed MRI-compatible frame specifically designed for iMRI. All surgeries were guided with the BrainLAB navigation system (BrainLAB, Munich, Germany) to ensure precision. iMRI was performed when the surgeon (M.T.) determined that maximum safe resection had been achieved or wished to assess surgical progress. The timing of iMRI was classified into three groups according to its intended purpose:
Group I: Confirmation of gross-total resection.
Group II: Confirmation of planned partial resection.
Group III: Interim evaluation of surgical progress.
This allowed for evaluation of the extent of resection, identification of any remaining tumor tissue, and assessment of surrounding structures.
Imaging data analysis
Images from contrast-enhanced bSSFP and T2WI were independently evaluated by two neurosurgeons (Yo.F. and T.N.) using a scoring system based on a previously published method13 to assess optic chiasm visibility: 0 – not visible; 1 – visible but unclear; 2 – clearly visible; and 3 – excellently visible (Fig. 1). All images were anonymized and presented in a randomized order to minimize rater bias. The sequence type (contrast-enhanced bSSFP or T2WI) was not labeled during evaluation. However, due to distinct imaging characteristics such as contrast and background signal, complete blinding could not be fully guaranteed. The evaluation focused specifically on the optic chiasm rather than the entire optic nerve. For comparison between sequences, we selected the image slice in which the chiasm was clearly visualized and matched the corresponding anatomical section across both contrast-enhanced bSSFP and T2WI sequences. While contrast-enhanced bSSFP has the technical advantage of thinner slice thickness (e.g., 0.7 mm), this was considered part of the sequence’s practical utility in the intraoperative setting. In cases of disagreement between the two neurosurgeons, a third neurosurgeon (M.K.) reviewed the images and provided the final decision.
[See PDF for image]
Fig. 1
Scoring criteria for assessing optic chiasm visibility. (A) 0 – not visible. (B) 1 – visible but unclear. (C) 2 – clearly visible. (D) 3 – excellently visible.
Statistical analysis
To evaluate the utility of different MRI sequences in depicting the optic chiasm, we compared preoperative contrast-enhanced bSSFP with preoperative T2WI. Furthermore, we compared intraoperative contrast-enhanced bSSFP with intraoperative T2WI. Median values and interquartile ranges were calculated for each sequence, and the Wilcoxon signed-rank test was used to identify statistically significant differences in paired scores between the sequences. Additionally, we analyzed factors contributing to a decrease in intraoperative contrast-enhanced bSSFP scores compared with preoperative contrast-enhanced bSSFP. Based on prior literature, the factors assessed were the presence of intracranial air and blood in the tumor cavity12. Fisher’s exact test was employed to examine the association between a decrease in contrast-enhanced bSSFP scores and the presence of these factors. Statistical significance was defined as p < 0.05 for all analyses.
Results
Patients
Eighteen patients (8 males, 10 females) were included in the study, ranging in age from their 20 s to their 70s. Pathological diagnoses included 12 cases of PitNETs, 3 craniopharyngiomas, 1 meningioma, 1 RCC, and 1 plasmacytoma. Among these, 7 were recurrent tumors. Compression of the optic chiasm by the tumor was observed in 11 cases (Table 1). Standard ETSS was performed in 16 cases, while extended ETSS was performed in 2 cases (case 7 and 11). According to the purpose of iMRI, 6 cases were classified as Group I, 7 as Group II, and 5 as Group III. Additional tumor resection was performed in 12 cases (Table 1).
Table 1. Clinical characteristics of Patients, preoperative and intraoperative Contrast-Enhanced bSSFP and T2WI Scores,and intraoperative findings related to score Decrease.
Case | Age | Sex | Pathology | Recurrence | Compression of Optic Chiasm | Purpose of iMRI | Additional tumor resection | preoperative | intraoperative | CE bSSFP Score Decrease | Intracranial Air | Blood in Tumor Cavity | ||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
CE bSSFP | T2WI | CE bSSFP | T2WI | |||||||||||
1 | 60s | M | PitNET | N | N | I | N | 3 | 2 | 3 | 2 | N | N | N |
2 | 40s | M | PitNET | N | Y | I | Y | 3 | 3 | 3 | 2 | N | N | Y |
3 | 20s | F | craniopharyngioma | Y | N | III | Y | 0 | 0 | 0 | 0 | N | N | Y |
4 | 50s | M | RCC | Y | Y | II | N | 3 | 1 | 2 | 1 | Y | Y | N |
5 | 40s | M | PitNET | N | N | II | N | 3 | 2 | 3 | 2 | N | N | N |
6 | 40s | F | PitNET | Y | Y | III | Y | 3 | 1 | 3 | 1 | N | N | Y |
7 | 60s | M | craniopharyngioma | Y | Y | I | N | 3 | 2 | 3 | 2 | N | Y | Y |
8 | 60s | F | PitNET | N | Y | I | Y | 3 | 3 | 1 | 1 | Y | Y | Y |
9 | 60s | F | PitNET | N | Y | II | Y | 2 | 0 | 2 | 1 | N | N | Y |
10 | 70s | M | plasmacytoma | N | N | II | Y | 3 | 3 | 2 | 1 | Y | N | Y |
11 | 50s | F | craniopharyngioma | N | Y | I | N | 2 | 2 | 0 | 0 | Y | Y | N |
12 | 40s | F | PitNET | Y | Y | II | Y | 3 | 2 | 2 | 1 | Y | Y | N |
13 | 40s | F | meningioma | N | N | III | Y | 2 | 1 | 2 | 2 | N | N | Y |
14 | 40s | F | PitNET | Y | Y | III | Y | 3 | 2 | 3 | 2 | N | N | N |
15 | 40s | M | PitNET | N | N | I | Y | 3 | 2 | 3 | 2 | N | N | N |
16 | 60s | F | PitNET | Y | N | III | Y | 3 | 2 | 3 | 2 | N | N | N |
17 | 60s | M | PitNET | N | Y | II | Y | 3 | 2 | 3 | 3 | N | Y | Y |
18 | 70s | F | PitNET | N | Y | II | N | 3 | 2 | 3 | 2 | N | Y | Y |
M = male; F = female; PitNET = pituitary neuroendocrine tumor; RCC = Rathke’s cleft cyst; Y = Yes; N = No; iMRI = intraoperative magnetic resonance imaging; I = Confirmation of gross-total resection; II = Confirmation of planned partial resection; III = Interim evaluation of surgical progress; CE bSSFP = contrast-enhanced balanced steady-state free precession; T2WI = T2-weighted image.
Preoperative and intraoperative contrast-enhanced bSSFP and T2WI scores
Table 1 presents the scores for preoperative and intraoperative contrast-enhanced bSSFP and T2WI. Among the preoperative contrast-enhanced bSSFP images, 7 cases were acquired using contrast-enhanced CISS and 11 cases using contrast-enhanced BFFE.
The median score for preoperative contrast-enhanced bSSFP was 3.0 (IQR: 2.75–3.0), significantly higher than the median score for T2WI (2.0 (IQR: 1.0–2.0); p = 0.0002) (Fig. 2A). For intraoperative imaging, the median score for contrast-enhanced bSSFP was 3.0 (IQR: 2.0–3.0), compared with 2.0 (IQR: 1.0–2.0) for T2WI. Similarly, the contrast-enhanced bSSFP scores were significantly higher than those for T2WI (p = 0.0002) (Fig. 2B).
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Fig. 2
Comparison of preoperative and intraoperative MRI scores for optic chiasm visualization. (A) Box plot comparing the median scores of preoperative contrast-enhanced bSSFP (3.0 (IQR: 2.75–3.0)) and preoperative T2WI (2.0 (IQR: 1.0–2.0)). The median score for contrast-enhanced bSSFP was significantly higher than that for T2WI (p = 0.0002), indicating better visualization with contrast-enhanced bSSFP. (B) Box plot comparing the median scores of intraoperative contrast-enhanced bSSFP (3.0 (IQR: 2.0–3.0)) and intraoperative T2WI (2.0 (IQR: 1.0–2.0)). The median score for contrast-enhanced bSSFP was significantly higher than that for T2WI (p = 0.0002), indicating enhanced visualization with contrast-enhanced bSSFP.
Decrease in intraoperative contrast-enhanced bSSFP score
Of the 18 cases, a decrease in the contrast-enhanced bSSFP score was observed in 5 cases. No cases showed an increase, while the scores in 13 cases remained unchanged (Table 1). In intraoperative contrast-enhanced bSSFP, intracranial air was detected in 7 cases, and blood in the tumor cavity was observed in 10 cases (Table 1).
Association of intraoperative contrast-enhanced bSSFP score decrease with intracranial air
To investigate the factors contributing to a decrease in intraoperative contrast-enhanced bSSFP scores, the patients were divided into two groups based on whether a score decrease was observed. Intracranial air was present in 7 cases, with 4 of these showing a score decrease. Conversely, among the 11 cases without intracranial air, only 1 case exhibited a score decrease. Fisher’s exact test revealed a statistically significant association between the presence of intracranial air and a decrease in the contrast-enhanced bSSFP score (p = 0.047) (Table 2).
Table 2. Association of decrease in intraoperative Contrast-Enhanced bSSFP score with presence of intracranial Air.
Intracranial air | Total | |||
---|---|---|---|---|
Yes | No | |||
Score decrease | Yes | 4 | 1 | 5 |
No | 3 | 10 | 13 | |
Total | 7 | 11 | 18 |
bSSFP = balanced steady-state free precession.
Association of intraoperative contrast-enhanced bSSFP score decrease with blood in tumor cavity
Among the 18 cases, blood in the tumor cavity was observed in 10 cases, with 2 of these showing a decrease in the contrast-enhanced bSSFP score. In the remaining 8 cases without blood in the tumor cavity, 3 cases exhibited a score decrease. Fisher’s exact test indicated no statistically significant association between the presence of blood in the tumor cavity and a decrease in the contrast-enhanced bSSFP score (p = 0.608) (Table 3).
Table 3. Association of decrease in intraoperative Contrast-Enhanced bSSFP score with presence of blood in tumor Cavity.
Blood in tumor cavity | Total | |||
---|---|---|---|---|
Yes | No | |||
Score decrease | Yes | 2 | 3 | 5 |
No | 8 | 5 | 13 | |
Total | 10 | 8 | 18 |
bSSFP = balanced steady-state free precession.
Review of cases with tumor-induced chiasm compression
A total of 11 cases exhibited tumor-induced compression of the optic chiasm, confirmed by preoperative contrast-enhanced bSSFP (PitNET in 8 cases, craniopharyngioma in 2 cases, and RCC in 1 case) (Table 1). Intraoperative contrast-enhanced bSSFP enabled visualization and assessment of the optic chiasm in 9 of these cases. Among these, 7 cases (case 2, 4, 7, 9, 12, 14, and 18) demonstrated successful decompression of the chiasm, while 2 cases (case 6 and 17) showed residual compression. In case 6, iMRI was performed for interim evaluation of surgical progress, and in case 17, for confirmation of planned partial resection. In both instances of residual compression, additional resection was performed, resulting in successful decompression of the chiasm. In 2 cases where the chiasm was not adequately visualized on iMRI (1 case with a score of 1 (case 8) and 1 case with a score of 0 (case 11), including one extended ETSS (case 11)), intracranial air was observed in both. For these cases, decompression of the chiasm was assessed based on observations in the surgical field, as iMRI could not confirm the condition. No cases in this study experienced postoperative deterioration in visual function.
Illustrative cases
Case 5
The patient was a male in his 40 s diagnosed with a PitNET. The tumor was confined to the sella turcica, with no evidence of optic chiasm compression (Fig. 3A). For optic chiasm visualization, the preoperative contrast-enhanced bSSFP score was 3 (Fig. 3B), while the preoperative T2WI score was 2 (Fig. 3C). Tumor removal was performed under general anesthesia using an ETSS approach. iMRI revealed no intracranial air or blood in the tumor cavity. The intraoperative contrast-enhanced bSSFP score was 3 (Fig. 3D), and the intraoperative T2WI score was 2 (Fig. 3E), demonstrating visualization comparable to the preoperative images.
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Fig. 3
(A) Sagittal contrast-enhanced T1WI showing the tumor confined to the sella turcica with no optic chiasm compression. (B) Preoperative imaging of optic chiasm visualization: contrast-enhanced bSSFP scored 3 and (C) T2WI scored 2. (D) Following endoscopic transsphenoidal tumor removal, iMRI detected residual tumor without intracranial air or blood. Intraoperative contrast-enhanced bSSFP scored 3 and (E) intraoperative T2WI scored 2.
Case 11
The patient was a female in her 50 s diagnosed with a craniopharyngioma. For optic chiasm visualization, the preoperative contrast-enhanced bSSFP score was 2 (Fig. 4A), and the T2WI score was also 2 (Fig. 4B). Tumor resection was performed using the ETSS approach. iMRI revealed significant intracranial air (Fig. 4C, D). The intraoperative contrast-enhanced bSSFP score was 0 (Fig. 4D), and the intraoperative T2WI score was likewise 0 (Fig. 4E).
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Fig. 4
(A) Optic chiasm visualization with preoperative contrast-enhanced bSSFP scored 2. (B) Optic chiasm visualization with preoperative T2WI scored 2. (C) After endoscopic transsphenoidal tumor resection, iMRI revealed significant intracranial air. (D) Intraoperative contrast-enhanced bSSFP scored 0 and (E) intraoperative T2WI scored 0.
Case 6
The patient was a female in her 40 s with a recurrent PitNET. The tumor extended from the sella to the suprasellar region, causing compression of the optic chiasm (Fig. 5A, B). For optic chiasm visualization, the preoperative contrast-enhanced bSSFP score was 3 (Fig. 5B), while the preoperative T2WI score was 1 (Fig. 5C). Tumor removal was performed under general anesthesia using the ETSS approach. In this case, iMRI was performed for interim evaluation of surgical progress, as this was a recurrent case and intraoperative anatomical landmarks were difficult to identify due to prior surgical changes. iMRI revealed the presence of blood in the tumor cavity but no intracranial air. The intraoperative contrast-enhanced bSSFP score was 3 (Fig. 5D), while the intraoperative T2WI score was 1 (Fig. 5E). Residual tumor was detected, and the optic chiasm remained slightly compressed (Fig. 5D). Following iMRI, additional tumor resection was performed, allowing for further debulking and resulting in successful postoperative decompression of the optic chiasm (Fig. 5F).
[See PDF for image]
Fig. 5
(A) Sagittal contrast-enhanced T1WI showing the tumor extending from the sella to the suprasellar region. (B) Preoperative contrast-enhanced bSSFP scored 3, revealing compression of the optic chiasm. (C) Preoperative T2WI scored 1. (D) Following endoscopic transsphenoidal tumor removal, iMRI detected residual tumor with blood in the tumor cavity. Intraoperative contrast-enhanced bSSFP scored 3 and (E) intraoperative T2WI scored 1. (F) Postoperative contrast-enhanced bSSFP confirmed successful decompression of the optic chiasm.
Discussion
In this study, intraoperative contrast-enhanced bSSFP was demonstrated to be superior to intraoperative T2WI for visualizing the optic chiasm during ETSS procedures. This finding aligns with the results observed in preoperative MRI. Furthermore, in cases where the visibility of the chiasm was reduced on intraoperative contrast-enhanced bSSFP compared with preoperative contrast-enhanced bSSFP, the presence of intracranial air during iMRI was identified as a potential factor contributing to the decline in image quality.
bSSFP is a fast MRI sequence that balances gradients along all axes, providing high signal intensity for tissues with high T2/T1 ratios. When combined with a contrast medium, bSSFP also delivers enhanced contrast14, making it a valuable tool for preoperative evaluation in ETSS. It is often considered superior to T2WI for these purposes. In this study, intraoperative contrast-enhanced bSSFP proved more effective than T2WI, allowing for more precise visualization of the optic chiasm. This enhanced visualization facilitated better evaluation of decompression and detection of potential chiasmal injuries. Access to such information intraoperatively can significantly support critical decision-making during surgery.
iMRI is generally considered less accurate than conventional preoperative or postoperative MRI. This discrepancy can be attributed to factors such as the presence of intracranial air or the placement of surgical instruments12. Additional factors may include significant deviation of the region of interest from the center of the gantry and the presence of blood within the tumor cavity. In this study, statistical analysis confirmed that intracranial air significantly contributed to the decrease in intraoperative contrast-enhanced bSSFP scores. This effect was particularly pronounced when the air was located near the optic chiasm because it caused magnetic field inhomogeneity that made visualization of the chiasm challenging. These findings are consistent with the susceptibility of bSSFP sequences to magnetic field inhomogeneity caused by air15. To mitigate image quality deterioration due to intracranial air, it is recommended to fill the surgical field with saline before performing iMRI. By contrast, the presence of blood in the tumor cavity did not impact the quality of contrast-enhanced bSSFP. Although blood can potentially degrade MRI quality, its effect in this study was minimal, possibly because the focus was on visualizing the optic chiasm. In cases where the chiasm was not compressed by the tumor, image quality appeared less likely to be affected by the presence of blood in the tumor cavity.
When visual impairment due to chiasmal compression is present, achieving effective decompression of the optic chiasm is one of the primary objectives of ETSS, including extended ETSS. Although the chiasm can sometimes be directly visualized in the surgical field after tumor resection, intraoperative views are often limited by the angle of access. iMRI provides comprehensive intraoperative visualization of the chiasm, surrounding structures, and any residual tumor, allowing objective assessment of surgical extent16. This capability makes iMRI a valuable complementary tool for guiding surgical decision-making. In this study, 11 cases exhibited preoperative chiasmal compression, and intraoperative contrast-enhanced bSSFP successfully evaluated the condition of the chiasm in 9 of these cases. In 2 cases where intraoperative contrast-enhanced bSSFP provided inadequate visualization of the chiasm, image quality degradation caused by intracranial air was observed. In these cases, the condition of the chiasm was assessed using direct endoscopic visualization of the surgical field. Among the two extended ETSS cases (cases 7 and 11), optic chiasm visualization was successful in case 7 but not in case 11, where intracranial air was present. As extended ETSS involves a wider surgical corridor, it may increase the risk of air entry, potentially degrading image quality.
In this study, we used contrast-enhanced bSSFP images because previous reports have indicated that gadolinium enhancement improves visibility. Additionally, in tumors with contrast enhancement, gadolinium administration allows for a more detailed and accurate assessment of the tumor, which has practical benefits. While intraoperative bSSFP may still be effective without gadolinium enhancement, this possibility warrants further investigation in future studies.
This study has several limitations. The small sample size and retrospective design highlight the need for further validation in larger, prospective cohorts. Additionally, preoperative contrast-enhanced bSSFP imaging included both contrast-enhanced CISS and contrast-enhanced BFFE, reflecting the variations in MRI equipment across our institution. The choice between CISS and BFFE was based on practical considerations because multiple MRI machines were utilized. Although these sequences are fundamentally similar and often considered interchangeable, the lack of standardization may have introduced variability. Future studies should aim to standardize MRI protocols to enhance consistency and strengthen the reliability of findings. Another limitation is related to the imaging evaluation process. Although all images were anonymized and randomized to reduce bias, experienced readers may have inferred the sequence type based on inherent image characteristics. This partial unblinding may have influenced the scoring process. Further studies could consider using multiple blinded raters and more standardized image presentation protocols to address this potential bias. Moreover, this study focused exclusively on the visibility of the optic chiasm. While the clinical significance of a difference between a score of 2 and 3 may be limited, obtaining clear iMRI could offer greater utility for visualizing other critical structures. Additionally, although the scoring system was based on a previously published method, the assignment of scores involved a degree of subjectivity, which may affect reproducibility. Of note, key structures involved in ETSS, such as the pituitary stalk and internal carotid arteries, were not evaluated in this study. However, the favorable imaging characteristics of contrast-enhanced bSSFP demonstrated for the optic chiasm suggest that this technique may also be applicable to these critical structures. Future research should expand to include these structures to provide a more comprehensive assessment of the utility of imaging techniques.
Conclusions
In this study, intraoperative contrast-enhanced bSSFP was found to be superior to T2WI for visualizing the optic chiasm, consistent with findings from preoperative MRI. However, the presence of intracranial air was identified as a factor that could potentially degrade the image quality of contrast-enhanced bSSFP.
Acknowledgements
The authors sincerely thank Yuichiro Somiya and Shintaro Horii for their invaluable support in the acquisition of magnetic resonance images for this study.
Author contributions
YoF: Conceptualization, Formal analysis, Data visualization, Investigation and Writing - original draft; MK: Conceptualization, Methodology, Investigation, Writing - original draft and Writing - review & editing; YuF and AF: Methodology, Investigation and Writing - review & editing; TN: Data visualization and Investigation; KT: Writing - review & editing; MT, EK, and TS: Supervision and Writing - review & editing. All authors reviewed the manuscript.
Data availability
All data generated or analysed during this study are included in this published article. For data requests, please contact the corresponding author.
Declarations
Competing interests
The authors declare no competing interests.
Abbreviations
balanced fast field echo
balanced steady-state free precession
constructive interference in steady-state
endoscopic transsphenoidal surgery
intraoperative magnetic resonance imaging
pituitary neuroendocrine tumor
Rathke’s cleft cyst
T2-weighted imaging
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Abstract
Preoperative balanced steady-state free precession (bSSFP) imaging is helpful in endoscopic transsphenoidal surgery (ETSS) for accurately evaluating the optic chiasm and surrounding structures. While intraoperative magnetic resonance imaging (iMRI) has been shown to improve surgical outcomes, the utility of intraoperative contrast-enhanced bSSFP remains underexplored. This study was performed to assess the effectiveness of intraoperative contrast-enhanced bSSFP compared with T2-weighted imaging (T2WI) for visualizing the optic chiasm and to identify factors affecting image quality. This retrospective study included patients who underwent ETSS between March 2015 and March 2020, with both preoperative and intraoperative MRI, including coronal contrast-enhanced bSSFP and T2WI sequences. Two neurosurgeons independently scored optic chiasm visibility using a 4-point scale (0–3). Statistical analyses involved paired comparisons of imaging scores and assessments of factors influencing intraoperative contrast-enhanced bSSFP quality, such as intracranial air and blood in the tumor cavity.Eighteen cases were analyzed. Contrast-enhanced bSSFP scores were significantly higher than T2WI scores for both preoperative imaging (median 3.0, IQR 2.75–3.0 vs. median 2.0, IQR 1.0–2.0; p = 0.0002) and intraoperative imaging (median 3.0, IQR 2.0–3.0 vs. median 2.0, IQR 1.0–2.0; p = 0.0002). A decrease in intraoperative contrast-enhanced bSSFP scores was observed in 5 cases and was significantly associated with intracranial air (p = 0.047) but not with blood in the tumor cavity (p = 0.608). Intraoperative contrast-enhanced bSSFP was superior to T2WI for optic chiasm visualization, consistent with preoperative findings. However, intracranial air significantly degraded the image quality of contrast-enhanced bSSFP.
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1 Kobe University Graduate School of Medicine, Department of Neurosurgery, Kobe, Japan (GRID:grid.31432.37) (ISNI:0000 0001 1092 3077)
2 Kobe University Graduate School of Medicine, Department of Neurosurgery, Kobe, Japan (GRID:grid.31432.37) (ISNI:0000 0001 1092 3077); Osaka Neurological Institute, Department of Neurosurgery, Toyonaka, Japan (GRID:grid.482869.9) (ISNI:0000 0004 0404 2005)
3 Kobe University Graduate School of Medicine, Department of Neurosurgery, Kobe, Japan (GRID:grid.31432.37) (ISNI:0000 0001 1092 3077); Toyooka Hospital, Department of Neurosurgery, Toyooka, Japan (GRID:grid.417247.3) (ISNI:0000 0004 0405 8509)
4 Kobe University Graduate School of Medicine, Department of Neurosurgery, Kobe, Japan (GRID:grid.31432.37) (ISNI:0000 0001 1092 3077); Kinki Central Hospital, Department of Neurosurgery, Itami, Japan (GRID:grid.415371.5) (ISNI:0000 0004 0642 2562)