Craniopharyngiomas Treated with the Inside-Out Subpial Technique during the Endoscopic Endonasal Approach: Surgical Technique Breakdown and Clinical Outcomes Over the Last 5 Years

Objective: Craniopharyngiomas are often mistakenly treated as extra-axial lesions, which can lead to microvascular damage, subsequent infarcts, and eventually result in hypothalamic or visual dysfunction. In this context, we explore the inside-out subpial surgical technique for resecting craniopharyngiomas during the endoscopic endonasal approach (EEA), as utilized in our clinical practice over the past 5 years.

Methods: The procedure entails a wide sellar, parasellar and suprasellar exposure in order to allow for adequate instruments’ maneuverability and dual-handed manipulation. Initially, the stalk is dissected while preserving the integrity of the subarachnoid space. Similar to the approach used in vestibular schwannoma surgery, internal debulking begins from an entry point on the tumor’s surface and the dissection plane with the normal stalk is established early on. Tumor removal then proceeds from the inside of the lesion toward the tuber cinereum, hypothalamus, and the chiasm, namely “inside-out.” This method typically results in a thin tissue layer remaining, thereby safeguarding the suprasellar microvasculature ([Fig. 1]). To further validate the technique's applicability, we conducted a retrospective review of all cases treated with this method at our institution from the beginning of 2019 to the end of 2023.

Fig. 1 Intraoperative photographs and schemes showcasing the “inside-out” technique as applied in craniopharyngioma endoscopic endonasal resection.

Results: During the study interval, 43 patients aged 44 years on average and harboring craniopharyngiomas underwent surgery in our center using the above-mentioned technique. Of those, 20 were females and 8 were under 18 years old. Mean tumor volume was 9 cm3, 35 tumors were adamantinomatous, 7 were papillary, whereas one was not specified. Fifteen patients had received previous treatment, and among all cases, visual deterioration was the most common presenting symptom (74%), followed by headaches (37%), and fatigue (21%). Gross total resection was accomplished in 27 patients (62%), near total in 8 (19%) and subtotal in the other 8 (19%). Mean length of hospitalization was 9 days and cerebrospinal fluid leak was the most frequently observed complication (13%). Two patients experienced slight visual field deterioration, with one returning to baseline, and no patients exhibited signs of hypothalamic infarct on postoperative MRI imaging. Complete preservation of pituitary function was achieved in two cases, whereas partial preservation, defined as either no need for DDAVP or no need for steroids, was attained in other 11. Tumor regrowth was noted in eight cases, with six patients receiving retreatment and a mean time to retreatment measured at 17.8 months.

Conclusion: The inside-out concept in treating craniopharyngiomas has been shown to significantly enhance the safety and effectiveness of the surgical procedure. That is, it enables a more extensive resection by more accurately defining the dissection plane further up in the third ventricle, while simultaneously reducing the risk of microvascular damage to the hypothalamus and chiasm.