How I do it: endoscopic endonasal resection of tuberculum sellae meningioma

Background Tuberculum sellae meningiomas (TSMs) adherent to neurovascular structures are particularly challenging lesions requiring delicate and precise microneurosurgery. There is an ongoing debate about the optimal surgical approach. Method We describe technical nuances and challenges in TSM resection using the endoscopic endonasal approach (EEA) in two cases of fibrous tumors with adherence to neurovascular structures. The cases are illustrated with a video (case 1) and figures (cases 1 and 2). Conclusion A dedicated team approach and precise microsurgical technique facilitate safe resection of complex TSMs through the EEA. Supplementary Information The online version contains supplementary material available at 10.1007/s00701-021-04784-5.


Introduction and relevant surgical anatomy
Tuberculum sellae meningiomas (TSMs) arise from the tuberculum sellae, limbus sphenoidale, and chiasmatic sulcus and tend to infiltrate the medial aspect of one or both optic canals [4]. This area is accessed with superb visualization through the endoscopic endonasal approach (EEA) [2]. Advantages of the EEA are early exposure and devascularization of the tumor base, decompression of the optic nerves from medial without brain or nerve retraction, and clear visualization of perforators to the optic apparatus and pituitary stalk. However, there seems to be a tendency to treat complex TSMs with transcranial approaches [3]. We illustrate the technical nuances on how to approach complex TSMs using the EEA without compromising on microsurgical technique.
Understanding the anatomy of the nasal cavity and paranasal sinuses is paramount for a safe and efficient endonasal approach to the anterior skull base. We carefully evaluate endonasal anatomy preoperatively, and in cases where the EEA is unsuitable, either due to pathology or significant anatomical variation, a transcranial approach is preferred. The tuberculum is laterally bordered by the tubercular crest, represented by the medial optico-carotid recess (mOCR) as seen from the EEA. The course of the optic nerves runs in the cisternal, preforaminal, intracanalicular, and intraorbital segments. The lateral optico-carotid recess corresponds to the optic strut and is a landmark for the intracanalicular segment. The dural fold of the limbus sphenoidale forms the falciform ligament as it extends laterally [1]. Small perforators and the superior hypophyseal artery (SHA) arise from the medial wall of the internal carotid artery (ICA) supplying the optic apparatus and the pituitary gland.

Description of the technique
Surgery is performed via a binostril 4-hand approach. The surgeons are standing slightly opposite, facing two different screens (Fig. 1), thus increasing the freedom of movements, ergonomics, and communication. The main authors (MW, DD) have established a routine of reversing roles every 30 min, where one surgeon primarily dissects, while the other provides visualization and assistance. This has increased workflow and efficiency, while reducing fatigue during long-lasting surgeries.
This article is part of the Topical Collection on Tumor -Meningioma A nasoseptal flap is harvested and placed in the nasopharynx. Septoplasty, bilateral uncinectomy with maxillary antrostomy, resection of the ethmoid bullae, and posterior ethmoidectomies are performed according to the endonasal anatomy for unhindered access. The middle turbinates are displaced laterally in the space created by this maneuver and can normally be spared. This is followed by a partial superior turbinectomy, a wide sphenoidotomy, posterior nasal septectomy, and removal of the sphenoid rostrum (Video).
Bone overlying the sella, parasellar ICAs, and planum is egg-shelled with a 4-mm coarse diamond burr and dissected off the dura. The tubercular strut is thinned, divided, and removed in pieces. Its lateral extension, the mOCR, corresponds to the preforaminal segment of the optic nerve and needs to be removed completely, together with the middle clinoid process, lying just inferiorly to the mOCR.
If there is evidence of tumor growth into the optic canal on preoperative MRI, the orbital apex and mOCR are exposed before decompressing the optic canal.
Once bony exposure is completed; the dural base of the tumor is devascularized. Dural opening starts with a vertical midline incision from the anterior tumor border to the upper border of the pituitary gland. Then, a horizontal cut, guided by neuronavigation, is made just in front of the anterior margin of the tumor (T incision). We believe this maneuver is safer than performing two laterally curved incisions just medial to the optic canals, as the remaining dural flaps involved with tumor can be gradually reflected and cut safely. Debulking of fibrous tumors is performed using ultrasonic aspiration and microsurgical piecemeal resection. Establishing arachnoidal dissection planes early and identifying areas of arachnoidal breach with adherence to, or encasement of, neurovascular structures is important for safe and efficient tumor removal (Fig. 2).
We establish a dissection plane anterior to the rostral tumor margin at the planum and identify the A2 segments. Tumor debulking is performed as we proceed to the inferior margin where tumor is separated from the pituitary gland and stalk. Often, the sellar diaphragm has to be resected to identify and preserve the pituitary stalk (Fig. 3). Tumor is mobilized and separated from the chiasm and optic nerves. Sharp dissection is performed to minimize the risk of injury to neurovascular structures and perforators supplying the optic apparatus ( Fig.  3 and Video). The optic nerves are followed to the optic canals where preforaminal, and if present, intracanalicular, tumor is resected.
The skull base defect requires meticulous reconstruction. We use collagen matrix (Duragen Plus, IntegraLifesciences) inlay and fascia lata onlay, covered by a vascularized nasoseptal flap. A fat graft is sometimes used for filling dead space (Fig. 4). We do not routinely use a lumbar drain and patients are mobilized the day after surgery [5].

Indications
TSMs without significant tumor growth lateral to the carotid arteries. Redo surgery and tumor involvement of vascular structures or the optic apparatus are not contraindications to the EEA, but require a skilled endoscopic skull base team.

Specific information to give to the patient about surgery and potential risks
Surgical risks related to anterior skull base surgery and EEA, in particular, visual and olfactory deterioration, endocrine dysfunction, and CSF leakage.
A summary of 10 key points 1. Operating room setup and patient positioning are important for optimal workflow, communication, and ergonomics during surgery.

Declarations
Ethical approval All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declarations and its later amendments or comparable standards.
Informed consent Informed consent was obtained from all individuals for publication of clinical data, photographs, and video material.

Conflict of interest
The authors declare that they have no conflict of interest.
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