Endoscopic Endonasal Modified Lothrop Approach to Anterior Cranial Fossa

40 Endoscopic Endonasal Modified Lothrop Approach to Anterior Cranial Fossa

Yi Chen Zhao, Peter-John Wormald, and Stephen Santoreneos

40.1 Introduction

The endoscopic endonasal modified Lothrop approach is an endoscopic approach, which provides access to the frontal sinus and the anterior skull-base, through a minimally invasive trans-septal, endonasal surgical route.

It is indicated in the treatment of lesions harboring from the anterior cranial fossa, located anterior to the anterior ethmoidal artery.

40.2 Indications

• Endonasal endoscopic modified Lothrop is an access procedure to the anterior cranial fossa that is required when the pathology extends or is located anterior to the anterior ethmoidal artery.

40.3 Patient Positioning

• Position: The patient is positioned supine in reverse Trendelenburg position.

• Body: The body is placed in reverse Trendelenburg with elevation of the head to 20° to the horizontal (Fig. 40.1).

• Head: The head is positioned neutrally to keep the skull base parallel to the endoscope pathway to avoid inadvertent injury to the skull base. Head is placed on a head ring.

• Instrument and surgeon setup: The monitor stack should be placed at the head of the patient making a straight line with the patient’s head and the surgeon. The right-handed surgeon typically will sit on the right side of the patient with the second surgeon standing behind. The scrub nurse stands on the contralateral side to the surgeon with the tray table facing the monitor (Figs. 40.2, 40.3).

40.4 Nasal Preparation

• Preparation of nasal cavity with topical local anesthetic and injections is carried out.

• Half strength betadine is used to prepare the face.

• Full strength betadine is used to prepare thigh for possible tensor fascia lata harvest.

• Image guidance system is set up and calibrated.

40.5 Soft Tissue Dissection

• Key landmarks to identify intra-nasally before the start of endoscopic Lothrop procedure are as follows:

◦ Nasal septum.

◦ Middle turbinate.

◦ Superior turbinate.

◦ Frontal sinus ostium.

◦ Nasal vault.

◦ Skull base.

• Typically, bilateral endoscopic middle meatal antrostomy, complete spheno-ethmoidectomy, and frontal recess dissection is performed first to identify the skull base from the planum sphenoidale to the posterior table of the frontal sinus.

Fig. 40.1 Patient setup with reverse Trendelenburg position with lateral thigh exposed for potential tensor fascia lata harvest.

• Resection of both middle turbinates is typically required to access the anterior skull base.

• If a skull base defect is anticipated, then a unilateral Haddad nasoseptal mucoperichondrial flap based on the posterior nasal artery is raised and placed into the posterior nasal space. A bilateral flap is raised if the entire skull base is resected.

• Middle meatal antrostomy followed by anterior ethmoidectomy, posterior ethmoidectomy, and sphenoidectomy is performed.

• The sphenoid sinus is then widely opened with removal of the anterior face of the sphenoid to clearly identify the skull base.

• Care needs to be taken when performing the sphenoidectomy that the pedicle of the nasoseptal flap is not injured along the anterior wall of the sphenoid sinus.

• A superior septectomy is then performed. Specific measurements are not given for the size of the septal window, as it needs to be tailored to individual patient’s anatomy (Fig. 40.4).

• The septal windows need to be large enough anteriorly to see the following:

◦ The contralateral frontal process of the maxilla.

◦ The ipsilateral middle turbinate (posteriorly).

◦ The contralateral axilla of the middle turbinate (inferiorly).

◦ The roof of the nasal cavity (superiorly).

• Anteriorly based lateral nasal mucosal flaps are raised bilaterally from the lateral nasal wall superior to the attachment of the middle turbinate. Posteriorly it extends 2 mm behind the axilla of the middle turbinate, superiorly to the roof of the nose, and inferiorly at the axilla of the middle turbinate.

Fig. 40.2 Positioning of video monitor and patient in line with the operative position of the surgeon.

Fig. 40.3 Setup of two-surgeons approach. Scrub nurse position opposite the surgeons.

40.6 Bone Exposure

• Bone removal begins with a high-speed drill (long endonasal attachment, 40° cutting burr) by directing it across the septal window to remove the bone of the ascending process of the maxilla (Figs. 40.4, 40.5).

• The bone removal is then directed superiorly from the frontal ostium into the frontal sinus. It is important to ensure that bone is removed superior-laterally first prior to moving medially to avoid inadvertent injury of the skull base (Fig. 40.6, 40.7).

• The procedure is repeated on the opposite side. The floor of the frontal sinus is removed. Any septation is also removed to create a single cavity to improve drainage from the frontal sinus to the nose.

• The mucosa over the roof of the nose is reflected until the first olfactory neurons are encountered. This location can further be confirmed with image guidance. This marks the anterior limit of the skull base and the posterior limit of the bony dissection of the endoscopic modified Lothrop procedure (Fig. 40.8).

• The remnant of the floor of the frontal sinus (“frontal T”) is lowered to the level of the skull base (Fig. 40.9).

• The remnant of the frontal beak of the maxilla is then removed with an angled cutting burr under 30° scope guidance until the anterior nasal skin is reached (Fig. 40.10).

• At the end of the bone removal, the entire skull base should be exposed from the sphenoid to the posterior table of the frontal sinus (Fig. 40.11).

• Anterior and posterior ethmoidal arteries are identified along the skull base or within their mesentry and are bipolar cauterized before divided with skull base scissors.