The recent development of endoscopic transnasal septal access may offer a new option for some patients with olfactory sulcus meningioma. Since olfactory sulcus meningioma originates from the ventral aspect of the skull base, the advantages of the transnasal approach are as follows: 1. direct control of the tumor blood supply (septal artery); and 2. resection of the paraneoplastic bone from the skull base. In some carefully screened patients, endoscopic transnasal surgery not only allows for perfect removal of the tumor, but also avoids the strain on the brain tissue caused by craniotomy.
Dr. Liu et al. from Rutgers University School of Medicine in New Jersey showed us the key points of endoscopic transnasal resection of olfactory sulcus meningioma, combining their experience and previous reports in the literature, as published in Neurosurg Clin N Am, July 2015.
Figure 1. A-C: MRI showing a case of olfactory sulcus meningioma suitable for endoscopic transnasal approach. The involved dura is confined to the surgical access and a “cortical sleeve” is visible separating the anterior cerebral artery. The base of the tumor shows hyperplastic bone, which will be removed during surgery; D-F: postoperative MRI shows that the tumor has been resected by Simpson grade I. The anterior skull base shows enhancement of the nasal septum mucosal flap.
Figure 2. Intraoperative photograph of tumor resection in Figure 1. A: endoscopic sieve plate (CP) at 30 degrees of elevation toward the ventral side of the skull base; B: endoscopic frontal sinus opening by modified Lothrop method, grinding the skull base bone in the coronal plane from the right side (RLP) toward the left sieve paper plate (LLP) and in the sagittal plane from the posterior wall of the frontal sinus (FS) toward the pterygoid plateau (PS). Electrocoagulation of the anterior skull base (ASB) dura to cut off the blood supply to the tumor; (C) sharp separation of the falx cerebri (black arrow) from anterior to posterior direction after opening the dura; (D-F) separation of the tumor (T) from the frontal lobe (FL) by a two-handed microdissection technique from outside the envelope
Preoperative evaluation
The anatomical boundaries of the transseptal passage were anterior wall (posterior wall of the frontal sinus), lateral wall (intraorbital wall or septal paper-like plate), and posterior wall (pterygoid plateau and saddle nodes). An endoscope with a 30-degree elevation angle provides a longitudinal view of the skull base ventral to the eye. Because the anterior and posterior sieve arteries are adjacent to the paranasal sinuses, the tumor vessels can be easily dissected. The choice of the appropriate surgical approach depends on the preoperative imaging features, especially the size and location of the tumor, the site and extent of dural involvement, the extent of peripheral vascular involvement, the extent of T2-weighted image changes (suggestive of soft membrane invasion), and operator preference.
The relative contraindications to the transnasal approach are as follows.
1. lateral extension of the tumor and attached dura mater to the orbital apex.
2. tumor growth anteriorly and superiorly (i.e., posterior wall of the frontal sinus)
3. tumor encapsulating blood vessels more severely.
4. the olfactory damage is mild or the patient has a strong desire to preserve the sense of smell.
If the involved dura at the base of the skull is confined between the two intraorbital walls, trans-EEA would be a good indication. In clinical practice, it is not uncommon to remove meningiomas in the olfactory sulcus without O removal of the sieve plate. Therefore, recurrent meningioma at the sieve plate with invasion of the paranasal sinuses is also a good indication for a transnasal approach (Figure 3).
Figure 3. A-C: CT and MRI showing a recurrent olfactory sulcus meningioma from the sieve plate with invasion of the inferior paranasal sinuses. This patient had a total bifrontal craniotomy, however, it recurred because the septal plate was not abraded. Note the hyperplastic bone on the sieve plate (A, white arrow); D-F: postoperative CT and MRI show endoscopic total resection of the tumor through a transnasal approach.
The transnasal approach has the following advantages: easier removal of tumor tissue invading into the sinuses, removal of the hyperplastic sieve plate, and repair of the skull base with a tipped nasal septal flap. If the tumor invades both the lateral and paranasal sinuses, a combined craniotomy and transnasal approach can be considered (Figure 4).
Figure 4. A-C: Preoperative MRI shows a recurrent olfactory sulcus meningioma invading the frontal and anterior septal sinuses. Because the affected dura extends to the orbital apex (white arrow) and is accompanied by osteophytes in the frontal bone and posterior wall of the frontal sinus, the tumor was completely resected by a double frontal craniotomy combined with an endoscopic transnasal approach. Because the cranial periosteum no longer existed, the skull base was repaired with a tipped nasal septal mucosal flap; D-F: postoperative MRI showed complete resection of the tumor.
Surgical techniques
1. Preoperative preparation and position
The patient should be placed in the supine position under general anesthesia with a three-point head frame fixation. When the operator is on the right side of the patient, the patient’s head should be slightly tilted to the right to facilitate intraoperative manipulation. The head should be slightly hyperextended to facilitate exposure of the septum. Intravenous antimicrobial agents for seizure prophylaxis and 10 mg dexamethasone were administered at the beginning of the procedure. Intraoperative MRI or/and CTA navigation is performed to clarify the extent of cranial exposure in the coronal and sagittal positions and the relationship with adjacent vessels.
The nasal cavity was disinfected with voltaic iodine and the nasal cavity was filled with hydroxymetazoline soaked gauze to constrict the nasal mucosal vessels. The thigh was prepared with skin to serve as an autologous fascial donor. We adopted a two-person bilateral team consisting of a neurosurgeon and an otolaryngologist. Intraoperative monitoring of somatosensory evoked potentials and motor evoked potentials was performed.
2. Endoscopic Intranasal Transseptal Approach
A 30-degree endoscope is the preferred option, and multiple views can be easily obtained intraoperatively by turning the endoscopic end. This coincides with the anatomical finding of Batra et al. that a 30-degree endoscope is more likely to reveal the ventral skull base from the frontal sinus to the pterygoid plateau than 0- and 70-degree endoscopes.
A mixture of 1% lidocaine and epinephrine (1:100,000) was injected into the septum and superior anterior middle turbinate. The inferior turbinates were retracted with a Goldman lift and the bilateral middle turbinates were excised to create septal access. Bilateral maxillary sinus openings were made to expose the orbital floor to provide anatomical landmarks. Bilateral pterygoid sinus dissection was performed with care to protect the vascular tip of the nasal septum in the posterior nasal arch.
The mid-nasal mucosal septal flap with vascular tip is separated and turned toward the posterior nasopharynx for skull base repair. The principle of septal flap design is to be as large as possible to adequately cover the skull base defect. The anterior margin is incised at the junction of the nasal column and the nasal septum and extended laterally. Care is taken to protect the vascular tip when separating to prevent damage to the blood supply of the septal flap.
The pterygoid sinus is incised and enlarged, and the septum is microdrilled to expose the palatoseptal suture. The frontal sinus is enlarged (modified Lothrop approach) to reveal the anterior border of the trans septal passage. The upper part of the septum is excised to facilitate a full ventral view of the sieve plate from both nostrils, and the posterior part of the septum may be excised to facilitate angulation of the instruments from both nostrils. The frontal sinus cavity was enlarged with an elevation scraper and high-speed drill and the nasofrontal opening was thinned to expose the posterior wall of the frontal sinus.
The modified endoscopic Lothrop approach is an important step in exposing the transseptal passage because it reveals the posterior wall of the frontal sinus (an important anatomic landmark of the anterior border of the transseptal passage).
The skull base is then opened with a high-speed drill (Figures 5-6). The extent of the skull base opening depends on the size of the tumor and the extent of its attachment to the dura mater. In general, the extent of cranial resection in the sagittal position is from the posterior wall of the frontal sinus to the pterygoid plateau in the coronal position, and the bone between the paper-like plates of the sieve on both sides. After thinning the palatal pterygoid suture and sieve plate, the coronoid is abraded and separated from the dural inversion surface. The anterior and posterior sieve arteries were electrocoagulated and separated to both sides to cut off the tumor blood supply. The proximal orbital portions of these two arteries are drawn with hasty retraction before electrocoagulation is complete to prevent intraorbital hematoma formation and protrusion of the eye. The dura mater exposed to the visual field should also be electrocoagulated to cut off the tumor blood supply from the dura mater.
Figure 5. Preoperative MRI (A, D) shows a large olfactory sulcus meningioma resected by a simple transnasal approach; postoperative CT (B, E) and 1-year postoperative MRI (C, F) show complete resection of the tumor with perfect skull base repair
Figure 6. Intraoperative photograph of the subdural resection of the tumor A: The septum is cut in the coronal plane from the right side (RLP) to the left septal paper-like plate (LLP) to reveal the anterior skull base (ASB) dura. As the tumor invades posteriorly, the dura of the pterygoid plateau is revealed in the sagittal plane. The pterygoid sinus (SS) can also be seen; B, C: after incision of the dura, the tumor (T) is operated with suction and micro-suction cutting drill for tumor reduction; D, E: the tumor is carefully separated from the frontal lobe from outside the envelope, and the tumor is removed from the nostril; F: pattern picture showing the frontal lobe after tumor removal
3. Subdural resection of tumor
The dura was incised medially in the sagittal position on the paper-like plate of the sieve bone. The anterior dural incision is transverse and the falx cerebri is sharply separated from anterior to posterior with angled surgical scissors. The posterior dural incision is made transversely across the pterygoid plateau. For larger tumors, the tumor can be disposed of by suction, ultrasound suction, or tumor lateralization suction for tumor reduction. For hard fibrous tumors, the above methods are less effective, and the tumor can be reduced by rotating the microsuction drill at an angle. In the process of tumor reduction, it should be noted that the tumor reduction instruments should be operated within the tumor envelope to prevent damage to the adjacent neurovascular structures.
After adequate tumor reduction, the tumor should be detached from outside the tumor envelope. To protect the surrounding brain tissue, the tumor should be detached from the arachnoid plane. However, since larger tumors are often associated with soft membrane invasion, subperitoneal resection is sometimes necessary for total resection of the tumor. Although the tumor may be larger than the surgical field, a lateral-to-central separation technique can collapse the tumor and expose it to the operative field.
Forced retraction of the tumor envelope before complete separation from the surrounding vascular and neural structures should be avoided to avoid catastrophic vascular injury. Sharply detach the important vessels around the tumor (especially the anterior cerebral artery). If the adhesion between the tumor and the surrounding vessels is severe, it is safer to leave part of the tumor tissue in order to avoid bleeding and permanent neurological deficits. Once the tumor tissue is removed, complete hemostasis should be achieved by placing a single layer of absorbable hemostatic gauze in the residual cavity.
4. Skull base reconstruction
Multilayer repair of the skull base is essential in preventing postoperative cerebrospinal fluid leakage. We recommend the three-layer repair method (Figures 7-9).
The first layer is an autologous fascia placed under the dura as a lining and covered with absorbable hemostatic gauze, with emphasis on the free edge of the fascia to fit tightly under the dura.
The second layer is the decellularized allograft dermis, which is placed between the skull and the dura mater, with a gentamicin-soaked gelatin sponge inserted between them. The free edge of the allograft dermis is folded back and covers the outside of the cranial margin of the defect as an outer lining (the part between the dura and the skull is used as an inner lining). This creates a gasket effect and thus ensures the tightness of the repair. If the skull base defect is small, the first layer may be autologous fascia or allograft dermis, and the second layer is still allograft dermis.
The third layer is a vascularized septal mucosal flap overlying the septal defect, which should be made so that the septal mucosal flap remains loose and tension-free when overlying the posterior wall of the frontal sinus. All three layers are reinforced and supported with quick-acting yarn and gentamicin-soaked gelatin sponge. The nasal cavity was filled with hemostatic cotton and removed 10-12 days postoperatively.
Figure 7. Schematic diagram of the three-layer repair approach for septal defects after transnasal resection of anterior skull base tumors (A: sagittal, B: coronal)
Figure 8. Intraoperative view of the three-layer skull base repair approach in patient Figure 5 A: frontal lobe tissue is revealed at the dural defect of the skull base (dotted line) after resection of the olfactory groove meningioma; B: autologous fascia (FL) is used as a lining; C: the second layer is decellularized allograft dermis (ADA), whose free edge is embedded between the skull and the dura and reinforced with gelatin sponge. The free edge of the allograft dermis is folded back and covered outside the skull edge of the defect as the outer lining (the part between the dura and the skull as the inner lining) to form a gasket effect and thus provide a good closure of the repair; D: the nasal septal mucosal flap (PNSF) (dotted line) forms the third layer of the skull base repair and is attached to the outside of the ADA; E, F: 3 months postoperative nasal endoscopy shows good anterior skull base mucosalization after the three-layer skull base repair. Note: LFS: left frontal sinus; LLP: left septal paper plate; LMS: left maxillary sinus; RFS: right frontal sinus; RLP: right septal paper plate; RMS: right maxillary sinus; SS: butterfly sinus; VP: vascular tip
Figure 9. Intraoperative view of the three-layer repair in patient A: decellularized allograft dermis (ADA1) was placed as the first layer under the anterior skull base dura; B: second layer of decellularized allograft dermis (ADA2); C: hemostatic gauze was laid outside ADA2; D: tipped nasal septal mucosal flap (PNSF) was flipped and covered over the skull base defect as the third layer. The three layers were reinforced and supported by hemostatic gauze and gentamicin-soaked gelatin sponge.
5. Postoperative management
(1) Postoperative broad-spectrum antibiotics were applied intravenously and changed to oral administration after 48-72 hours until the nasal stuffing was removed (10-12 days postoperatively).
(2) Pay attention to the prevention of deep vein thrombosis during and after surgery, and it is recommended to start bedtime activities on the first day after surgery.
(3) CT scan of the head should be performed immediately after surgery, and MRI scan of the head should be checked on the first day after surgery.
④If the brain tissue edema is severe before and after surgery, dexamethasone should be applied and discontinued after 5-7 days. ⑤ Routine seizure prophylaxis should be discontinued after 6 weeks in the absence of seizures.
6. Management of complications
Complications include cerebrospinal fluid leak, vascular injury, paranasal sinus infection, brain abscess, convulsions, hydrocephalus, hyposmia, respiratory failure, deep vein thrombosis, and pulmonary embolism.
Cerebrospinal fluid nasal leakage is the most common complication of endoscopic transnasal olfactory groove meningioma resection. Once identified we recommend endoscopic exploration and reparation.
The arteries that may be injured intraoperatively include the frontal orbital artery, frontopolar artery, anterior cerebral artery, anterior communicating artery, and Heubner’s reentrant artery. Injury to these arteries can lead to intraoperative hemorrhage, infarction, and corresponding functional deficits. Strict intraoperative hemostasis is required. Early and delayed postoperative angiography should be performed to rule out early and late pseudoaneurysm formation.