The clinical characteristics according to the RCC type in 42 patients (30 females; mean age at surgery, 53.0 ± 18.0 years) are summarized in Table 1 (see Supplementary Table 1 for detailed information). Sixteen patients had AI and three had DI, preoperatively. For other pituitary axes, hypogonadism was identified in 10 patients, hypothyroidism in 11, and growth hormone deficiency in 19. Hyperprolactinemia was identified in 17, which resolved within one year after surgery except for one patient. The mean postoperative period was 3.9 ± 2.3 years and four required reoperation for early recurrence. Twenty patients (47.6%) were histologically diagnosed with RCCs. Cyst-wall opening was consistently associated with an intraoperative CSF leak; however, no patient required repair procedures for postoperative CSF leakage. As for postoperative pituitary dysfunction, 17 patients had AI (11 in type A, three in type B, three in type C) and eight patients had DI (five in type A, two in type B, one in type C).

Type-A RCCs were found in 14 patients, of whom 13 (92.9%) were women, accounting for the highest proportion among the three types (p = 0.086, chi-squared test). The rate of preoperative pituitary dysfunction was the highest in type A among the three types (Table 1, p = 0.0071 [vs. types B and C], p = 0.0041 [vs. type B], p = 0.0041 [vs. type C], chi-squared test).

For MRI findings, cyst-wall enhancement was observed in 13 cases (92.9%), which was significantly more frequent than that for type C (p < 0.01, chi-squared test). Figure 1 shows the imaging and intraoperative findings in a representative type-A case.

Representative recurrent case for type A Rathke’s cleft cyst (Patient No. 1). (a) T1-weighted image (T1WI) and (b) T2-weighted image (T2WI) showing mixed low and high signal intensity in the cyst; (c) Contrast-enhanced T1WI showing cyst wall enhancement; (d) T1WI obtained at the time of cyst recurrence showing high signal intensity in the lateral part of the cyst; (e) T2WI obtained at the time of recurrence showing mixed low and high signal intensity in the cyst; (f) Intraoperative findings at recurrence showing purulent contents on the lateral side of the cyst

Because of the purulent appearance of the cyst contents, bacterial cultures were performed in 11 cases, six of which were positive. To avoid secondary infection such as meningitis, we initially had not opened the wall for type A. However, we experienced three cases with early recurrence: each had a larger cyst with suprasellar extension and, for one patient, the cyst wall was not opened because purulent content remained at the margin of the cyst (Fig. 1D-F). In fact, the patient underwent five TSS procedures within 1–2 years interval due to reaccumulation from the remnant content. This patient was cured by cyst-wall opening after completely evacuating the cyst contents with curved aspiration and extensive irrigation, and there was no recurrence for more than 3 years. The same strategy was applied in two other recurrent cases, resulting in no further recurrence. In total, three patients underwent cyst-wall opening and 11 patients did not, with no significant differences in early recurrence rates by surgical technique in type A (Table 2).

Type-B RCCs were observed in 14 patients. Figure 2 shows the imaging and intraoperative findings in a representative type-B case. Intracystic nodules were detected in eight patients (57.1%), which was the highest rate among the three types (p = 0.011 [vs. types B and C], p = 0.0031 [vs. type A], p = 0.015 [vs. type C], chi-squared test). Signal intensity on MRI differed across cases and cyst-wall enhancement was observed in eight cases (57.1%). Cyst-wall opening was performed in eight cases (57.1%), and no cases required reoperation within 2 years after surgery.

Representative case for type B Rathke’s cleft cyst (Patient No. 22). (a) Axial T1-weighted image (T1WI) showing iso or high intensity in the cyst; (b) Coronal T1WI showing nodule in the cyst; (c) Coronal T2-weighted image (T2WI) showing iso to low intensity in the cyst; (d) Sagittal T1WI showing compression of the optic nerve by the cyst; (e) Sagittal T2WI showing compression of the optic nerve by the cyst; (f) Intraoperative high-magnified image under a microscope showing that the content of the opened cyst was a clear, low-viscosity liquid with a slight whitish tinge

Type-C RCCs were found in 14 patients with a mean age of 65.4 ± 10.4 years, which was significantly older than that of the other groups (p = 0.0033, Kruskal–Wallis; p = 0.0054 [vs. type A], p = 0.0038 [vs. type B], Wilcoxon rank-sum test).

The cysts showed T1 low and T2 high intensity on MRI and could be reliably distinguished from the other types. As shown in Table 1, the mean cyst volume was larger and the rate of cyst-wall enhancement was significantly less than those in the other groups (p < 0.01[vs. types B and C], p < 0.0001 [vs. type A], p = 0.00026 [vs. type B], chi-squared test).

Early recurrence was observed in a patient in whom the cyst wall was not opened at the initial surgery due to old age (Fig. 3). After this experience, the cyst wall was opened in all patients with this type of RCC. There was no recurrence within 2 years after the first operation, although the content was slightly reaccumulated with a change in the MRI intensity in one case.

Representative case for type C Rathke’s cleft cyst (Patient No. 32). (a) T1-weighted image (T1WI) showing low intensity in the cyst; (b) T2-weighted image (T2WI) showing high intensity in the cyst; (c) Intraoperative findings showing the thin cyst wall, and when it was cut, clear, watery content flowed out; (d) T2WI obtained 1 week postoperatively showing that the cyst is shrinking; (e) T2WI obtained 3 months postoperatively showing that the cyst had reaccumulated and the optic nerve is compressed; (f) Intraoperative findings at the time of cyst recurrence showing that the cyst and cyst wall were opened and the optic nerve is observed under endoscope

The clinical data of 74 patients with asymptomatic RCCs (53 females, mean age 45.2 ± 19.0 years) were available. Type C cysts were detected in nine patients (12.2%) with asymptomatic RCCs, which was significantly fewer than in the symptomatic group (14/42, 33.3%; p = 0.006, chi-squared test).