Inner and outer retinal layer thickness alterations in pediatric and juvenile craniopharyngioma

We evaluated postoperative retinal thickness in pediatric and juvenile craniopharyngioma (CP) patients with chiasmal compression using optical coherence tomography (OCT) auto-segmentation. We included 18 eyes of 18 pediatric or juvenile patients with CP and 20 healthy controls. Each thickness of the macular retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer, outer plexiform layer, outer nuclear layer, and photoreceptor layer was compared between the CP patients and healthy controls. There was significant thinning in the macular RNFL (estimates [μm], superior, − 10.68; inferior, − 7.24; nasal, − 14.22), all quadrants of GCL (superior, − 16.53; inferior, − 14.37; nasal, − 24.34; temporal, − 9.91) and IPL (superior, − 11.45; inferior, − 9.76; nasal, − 15.25; temporal, − 4.97) in pediatric and juvenile CP patients postoperatively compared to healthy control eyes after adjusting for age and refractive errors. Thickness reduction in the average and nasal quadrant of RNFL, GCL, and IPL was associated with peripapillary RNFL thickness, and reduced nasal quadrant GCL and IPL thicknesses were associated with postoperative visual field defects. In pediatric and juvenile patients with CP, decreased inner retinal layer thickness following chiasmal compression was observed. The changes in retinal structures were closely related to peripapillary RNFL thinning and functional outcomes.

www.nature.com/scientificreports/ function in patients who are unable to cooperate with visual acuity testing 18 . Gu et al. reported that GCC thickness measured by OCT could distinguish between patients with and without a loss of visual function from optic pathway glioma 19 . Yang et al. studied OCT results in eyes with CP and reported that the GCC thickness was sensitive in detecting optic nerve injury especially in pediatric or juvenile patients 20 . Bialer et al. also reported that a thinner RNFL on OCT was well-correlated with poorer visual acuity and VF defects in pediatric CP 10 . However, there have been no studies on changes in the whole retinal layer using retinal segmentation analysis in pediatric and juvenile patients with CP. In this study, we evaluated changes in both the inner and outer retinal layer thicknesses in pediatric and juvenile patients with CP compared to healthy controls using OCT autosegmentation software and analyzed the association between retinal layer thickness and other ocular structural and functional parameters.

Results
This study included a total of 18 eyes of 18 patients with pediatric and juvenile CP and 20 eyes of 20 healthy controls. Except for only one patient with papillary type CP, all patients were diagnosed with adamantinomatous CPs histologically. The mean age was 11 ± 4 years in patients with CP, and 10 ± 4 years in the healthy controls (p = 0.3310). There were significant differences in visual acuity between the two groups (p = 0.0360). Also, there was a significant thinning of the peripapillary RNFL in the patient group compared to the healthy controls (p < 0.0001). In the patient group, 12 patients had permanent hemianopsia with visual acuity greater than 20/40, and two patients had permanent loss of both the VF and visual acuity after tumor resection. VF testing was not performed in four patients due to poor cooperation (Table 1). Table 2 presents the results of each retinal layer thickness in four quadrants of the two groups. A significant difference was observed in almost all quadrants of the macular RNFL (estimates (standard error), superior, − 10 (1.12), p = 0.0024) between the patients with CP and the healthy controls after adjusting for age and spherical equivalent (SE). No significant difference was detected in the inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), or photoreceptor layer (PRL) thickness between the two groups.
To compare the retinal layer thickness between the eye with better visual function and the eye with poor visual function in the CP patients, we performed a subgroup analysis. Table 3 presents the measurements of each retinal layer thickness in four quadrants of the worse eye (worse VF) and better eye (better VF) in the CP patients compared to the controls. The mean thickness of the RNFL, GCL, and IPL was less in the worse eye group than in the better eye group. However, the differences did not reach statistical significance. Both the better eye and worse eye groups showed significant differences in RNFL, GCL, and IPL thickness compared to the control group in most sectors (all p < 0.05). Table 4 and Fig. 1 present the associations between postoperative intraretinal layer thickness and other ocular parameters. Peripapillary RNFL thickness was associated with macular RNFL (r = 0.7450, p = 0.0004), GCL (r = 0.7739, p = 0.0002), and IPL (r = 0.8257, p < 0.0001) thickness. Regarding the functional parameters, postoperative VF defects were associated with the thickness of the nasal quadrant GCL (r = 0.6806, p = 0.0074) and IPL (r = 0.5662, p = 0.0348). The postoperative best-corrected visual acuity (BCVA) was also associated with the average value of GCL, nasal quadrant GCL (r = − 0.7162, p = 0.0008; r = − 0.5413, p = 0.0203) and nasal quadrant INL (r = 0.4962, p = 0.0362) thickness.

Discussion
Compared to pituitary adenoma, which is the most common type of sellar tumor in adults, CP is known to be deep-seated, with a midline location and intimate relationship with critical neurovascular structures, leading to increased struggles in surgical removal 21 . Mediero et al. reported that 60% of the eyes with CP had a BCVA below 20/40, and VF defects were more frequently observed than the loss of visual acuity after surgery 22 . Also, Wan et al. reported that 58% of the CP patients had visual impairment in at least one eye at the final follow-up 23 . In contrast, in pediatric patients with pituitary adenoma, only 6% of the pediatric patients presented with permanent visual dysfunction after surgery 24 . Also, the visual outcomes of patients with pediatric CP are reported to be poorer than  25 . They reported that adult CP patients tended to have more subtle VF changes, such as generalized field constriction and central scotoma 25 .
Retinal layer thinning in chiasmal compression or other optic neuropathies was reported to be caused by retrograde degeneration 26,27 . In animal studies, a complete loss of ganglion cells in the medial retina was found after axonal injury due to chiasmal compression 28 . This was also confirmed by OCT studies in adult patients with chiasmal compression 29,30 . Previous studies using OCT reported inner-retinal layer thinning following chiasmal compression 29,30 . Akashi et al. reported that macular inner retinal layer thinning in the nasal hemiretina had diagnostic value for band atrophy due to chiasmal compression 29 . Monteiro et al. also evaluated macular inner retinal layer thickness using OCT in eyes with band atrophy due to chiasmal compression 30 and reported that band atrophy led to macular RNFL, GCL, and IPL thinning and INL thickening. And, segmented retinal layer analysis was suggested to be a useful tool for the assessment of structure-function relationships in patients with temporal VF defects 30 . Reports on the OCT results in pediatric tumors involving the visual pathway are relatively scarce compared to studies in the adult population, and there have been a few reported studies using OCT in pediatric patients with optic pathway glioma 9,18,19 and CP 10,22 . Avery et al. reported that in optic pathway glioma, decreased RNFL thickness was correlated with low visual acuity or VF deficits 18 . Gu et al. also reported that GCC thickness had discriminatory ability between normal and abnormal vision in patients with optic pathway glioma 19 . Since the use of other visual functional testing is often limited in pediatric patients due to the lack of cooperation, Banc et al. suggested that OCT may serve as a potential tool for screening or follow-up examinations in children with optic pathway glioma 9 . In 20 pediatric patients with CP, Bialer et al. demonstrated peripapillary RNFL thinning and a significant correlation between peripapillary RNFL thickness and visual acuity and Table 2. Comparison of intraretinal layer thickness between pediatric and juvenile craniopharyngioma patients and healthy controls. Significant values are indicated in bold. N numbers, RNFL retinal nerve fiber layer, GCL ganglion cell layer, IPL inner plexiform layer, INL inner nuclear layer, OPL outer plexiform layer, ONL outer nuclear layer, PRL photoreceptor layer. *P-values obtained by linear regression were adjusted for age and SE and Bonferroni's correction multiplied by 28.  20 . The GCC thickness in the pediatric and juvenile CP patients was significantly thinner than that in the adult CP patients and reflected more severe retinal structural degeneration due to retrograde degeneration 28 following axonal damage in pediatric and juvenile CP patients compared to adult CP patients 20 .
In this study, we first performed whole retinal layer segmentation analyses in pediatric and juvenile patients with CP. Previous studies in adult patients with chiasmal compression revealed pathologic changes in various retinal layers such as the INL 30 , IPL 31,32 , and PRL 31 following chiasmal compression and significant association between the thinning of retinal layers and visual prognosis 29,32 . We also found a significant thinning of the RNFL, GCL, and IPL in pediatric and juvenile CP patients compared to healthy controls. Otherwise, no significant alterations were observed in the INL, OPL, ONL, and PRL in patients with CP. We also found that the nasal GCL and IPL thickness was associated with the degree of postoperative VF defects, which suggests that retinal layer thickness changes represent postoperative visual function in these subjects. Retinal layer segmentation analysis, especially including inner retinal layers such as the GCL and IPL, might be useful for the postoperative follow-up of pediatric and juvenile CP patients.  www.nature.com/scientificreports/ A number of important limitations should be considered when interpreting the data from our study. First, we used a retrospective cross-sectional design, thereby limiting our ability to reveal the temporal aspects of changes in the OCT parameters. Second, our dataset was relatively small and the patients were inconsistently followed after decompression surgery. This was uncontrollable with a retrospective design. Ultimately, a larger longitudinal cohort study is needed to observe the serial changes in intraretinal layer thicknesses. Third, since this was an exploratory study, and a primary analysis was not planned before the study, all results should be read as descriptive and interpreted with caution 33 .
In conclusion, this study revealed inner retinal layer degeneration in pediatric and juvenile CP patients with chiasmal compression. The nasal GCL and IPL thicknesses were associated with the degree of postoperative VF defects. These results suggest that retinal layer segmentation analysis using OCT may be a useful tool in estimating the degree of functional damage in pediatric CP patients.

Methods
Study participants. This retrospective case-control study included 18 patients with pediatric and juvenile CP and 20 healthy controls at the Neuro-ophthalmology Department of Samsung Medical Center between March 2012 and April 2020. This study was conducted according to the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board of the Samsung Medical Center (Seoul, Republic of Korea, IRB No. 2018-06-085-003). Informed consent was waived for the patients with chiasmal compression by the Institutional Review Board of the Samsung Medical Center (Seoul, Republic of Korea). For all included patients, the clinical diagnosis of chiasmal compression with CP was based on magnetic resonance imaging (MRI) evidence of tumor compression of the optic chiasm and pathologically confirmed as CP postoperatively. All patients underwent a trans-sphenoidal approach or open craniotomy with tumor resection. Seven patients also received adjuvant radiotherapy. All patients were followed up for at least 6 months after surgery. The control group consisted of 4 to 17-year-old healthy volunteers who underwent routine eye examinations. Written informed consent was obtained from their legal guardians and, when appropriate, the healthy children, before enrollment. None of the controls had a history of ocular or neurologic disease. The healthy controls were required to have normal visual acuity, a normal intraocular pressure of ≤ 21 mmHg, and normal optic discs. The following categories of patients or healthy controls were excluded: those diagnosed with other ophthalmic diseases (glaucoma, a refractive error greater than + 6.0 diopters of SE or less than − 6.0 diopters of spherical equivalent, astigmatism of 3.0 diopters or more, amblyopia, epiretinal membrane, age-related macular degeneration, diabetic retinopathy, retinal artery/vein occlusion, optic neuritis, or other ischemic optic neuropathy) and previous retinal surgery that affected the thickness of the intra-retinal layer, and those diagnosed with known systematic/inflammatory diseases such as cancer and multiple sclerosis.
Ophthalmic examinations. All subjects were scanned using fundus color photography and spectraldomain OCT (SD-OCT, Spectralis, Heidelberg Engineering, Heidelberg, Germany). The VF perimetry of the patients was measured with a Humphrey Field Analyzer using the 30-2 SITA-standard protocol (Humphrey 740 Visual Field Analyzer, Carl Zeiss Meditec Inc. Dublin, CA). Only reliable VFs (≤ 33% false positives and false negatives; fixation losses of < 20%) were used in the study. The mean deviation (MD) was used for analysis. Table 4. Association analysis of postoperative intra-retinal layer thickness versus visual field defects, visual acuity, and peripapillary retinal nerve fiber layer thickness. Significant values are indicated in bold. RNFL retinal nerve fiber layer, pRNFL peripapillary retinal nerve fiber layer, VF visual field, MD mean deviation, BCVA best-corrected visual acuity, GCL ganglion cell layer, IPL inner plexiform layer, INL inner nuclear layer, OPL outer plexiform layer, ONL outer nuclear layer, PRL photoreceptor layer. *Pearson's correlation analysis. † Spearman's correlation analysis. Seven retinal layers were identified via automated segmentation using Spectralis software with manual correction as needed. The thickness of each layer between the vitreoretinal interface and the outer border of the retinal pigment epithelium was measured automatically. The whole retinal layer was segmented into seven respective retinal layers: the RNFL, the GCL, the IPL, the INL, the OPL, the ONL, and the PRL. Following the automated segmentation of each retinal layer, the thickness of each retinal layer in the 3-and 6-mm subfields www.nature.com/scientificreports/ as defined by the ETDRS grid was automatically measured using the Spectralis mapping software (Fig. 2). The average thickness of the four macular quadrants measured within the 3 mm and 6 mm zones was calculated for each layer. The segmentation was based on a validated algorithm used to measure the average thickness values within a 3 × 3 mm circle and a 6 × 6 mm extended area centered at the fovea. The foveal region, consisting of a 1 × 1 mm circle, was excluded from the analysis. The quality of all images was reviewed by two independent graders (G.I.L. and K.A.P.). We manually corrected any errors in the automated segmentation, as reported previously by Oberwahrenbrock et al. 34 .
Statistical analysis. The demographic and clinical characteristics of the CP patients and healthy controls are presented as standard descriptive summaries (e.g., means and standard deviations for continuous variables such as age, and percentages for categorical variables such as gender). The BCVA was converted to a logarithmic scale (logMAR). The chi-squared test was used to compare categorical variables such as gender between the groups. The Mann-Whitney U test was used to compare clinical characteristics such as age, SE, BCVA, and peripapillary RNFL thickness between the group of patients and the healthy controls. The intraretinal layer thickness of the patients was compared to that of the healthy controls using linear regression analysis adjusting for age and SE. We divided all CP patients into two groups of the worse eye and better eye and performed subgroup analysis using the paired t-test and independent t-test. Bonferroni's correction for multiple comparisons was applied to the p-values by multiplying the uncorrected p-values by 28 in the main anlaysis and the subgroup analysis. Pearson's and Spearman's correlation coefficients were calculated to analyze the association between intra-retinal layer thickness and functional parameters and peripapillary RNFL thickness. A p-value of less than 0.05 was considered statistically significant. All statistical analyses were performed with SAS version 9.4 (SAS Institute, Cary, NC, USA).

Data availability
The datasets generated during and/or analyzed during the current study are available from the corresponding author upon reasonable request.