An Alternative Endoscopic Anterolateral Route to Meckel's Cave: An Anatomic Feasibility Study Using a Sublabial Transmaxillary Approach

Anterior endoscopic sublabial transmaxillary access to middle cranial base lesions

BACKGROUND

Anterior endoscopic access to middle cranial base lesions becomes feasible in the presence of infratemporal fossa (ITF) involvement. Various approaches, including endoscopic endonasal, transoral sublabial, and transorbital methods, have been described for accessing the ITF through a transmaxillary corridor. Among these approaches, endonasal access is the most commonly preferred, while the transorbital approach is a novel technique gaining popularity. The transoral sublabial approach is considered suitable for selected lesions.

METHODS

Patients who underwent the anterior endoscopic transoral/sublabial transmaxillary approach to middle cranial base lesions at a single institute from 2016 to 2023 were included in this retrospective study. Malignant lesions were excluded from the study. The sublabial approach was exclusively performed in all cases, with the exception of one patient who required a combined approach.

RESULTS

The anterior endoscopic transoral sublabial transmaxillary approach to the infratemporal fossa, upper parapharyngeal space, and middle cranial fossa was performed on 14 patients. The underlying conditions for these patients were as follows: trigeminal schwannomas (n = 8), meningiomas (n = 2), juvenile nasopharyngeal angiofibroma, osteochondroma, arachnoid cyst and encephalocele (n = 1 each). Gross total resection was achieved in 11 cases. The most common complication was numbness in the territory of the maxillary and mandibular nerves (n = 4). Two patients needed endoscopic maxillary antrostomy for persistent suppuration. No wound problems or CSF rhinorrhea occurred. The average follow-up time was 26.6 months.

CONCLUSION

The endoscopic sublabial transmaxillary approach provides direct access to the infratemporal fossa and middle cranial base, enhancing the surgical range of maneuverability while sparing the sinonasal cavity. This procedure is safe, less invasive, and could be used as an efficient corridor for the resection of selected infratemporal fossa lesions with or without extension to the middle cranial base and parapharyngeal space.

Indications and outcomes of endoscopic transorbital surgery for trigeminal schwannoma based on tumor classification: a multicenter study with 50 cases

OBJECTIVE

Trigeminal schwannoma is a rare CNS tumor and involves the multicompartmental skull base. Recently, the endoscopic transorbital approach (ETOA) has emerged as a technique for minimally invasive surgery. The objective of this study was to evaluate the optimal indications and clinical outcomes of the ETOA for trigeminal schwannomas based on their tumor classification.

METHODS

Between September 2016 and February 2022, the ETOA was performed in 50 patients with trigeminal schwannoma at four tertiary hospitals. There were 15 men and 35 women in the study, with a mean age of 46.9 years. All tumors were classified as type A (predominantly involving the middle cranial fossa), type B (predominantly involving the posterior cranial fossa), type C (dumbbell-shaped tumors involving the middle and posterior fossa), or type D (involvement of the extracranial compartment). Type D tumors were also subclassified by ophthalmic division (D1), maxillary division (D2), and mandibular division (D3). Clinical outcome was analyzed, including extent of resection and surgical morbidities.

RESULTS

In this study, overall gross-total resection (GTR) was performed in 35 (70.0%) of 50 patients and near-total resection (NTR) in 9 patients (18.0%). The mean follow-up period was 21.9 (range 1-61.7) months. There was no tumor regrowth or recurrence during the follow-up period. Based on the classification, there were 17 type A tumors, 20 type C, and 13 type D. There were no type B tumors. Of the 13 type D tumors, 7 were D1, 1 D2, and 5 D3. For type A tumors, GTR or NTR was achieved using an ETOA in 16 (94.1%) of 17 patients. Eighteen (90.0%) of 20 patients with type C tumors attained GTR or NTR. Ten (76.9%) of 13 patients with type D tumors underwent GTR. Statistical analysis showed that there was no significant difference in the extent of resection among the tumor subtypes. Surgical complications included transient partial ptosis (n = 4), permanent ptosis (n = 1), transient diplopia (n = 7), permanent diplopia (n = 1), corneal keratopathy (n = 7), difficulties in mastication (n = 5), and neuralgic pain or paresthesia (n = 14). There were no postoperative CSF leaks or enophthalmos during follow-up.

CONCLUSIONS

This study showed that trigeminal schwannomas can be effectively treated with a minimally invasive ETOA in all tumor types, except those predominantly involving the posterior fossa (type B). For the extracranial compartments, D2 or D3 tumor types often require an ETOA combined with the endoscopic endonasal approach, while D1 tumor types can be treated using an ETOA alone.

A subset of arachnoid granulations in humans drain to the venous circulation via intradural lymphatic vascular channels

OBJECTIVE

The discovery of dural lymphatics has spurred interest in the mechanisms of drainage of interstitial fluid from the CNS, the anatomical components involved in clearance of macromolecules from the brain, mechanisms of entry and exit of immune components, and how these pathways may be involved in neurodegenerative diseases and cancer metastasis. In this study the authors describe connections between a subset of arachnoid granulations (AGs) and the venous circulation via intradural vascular channels (IVCs), which stain positively with established lymphatic markers. The authors postulate that the AGs may serve as a component of the human brain's lymphatic system.

METHODS

AGs and IVCs were examined by high-resolution dissection under stereoscope bilaterally in 8 fresh and formalin-fixed human cadaveric heads. The superior sagittal sinus (SSS) and adjacent dura mater were immunostained with antibodies against Lyve-1 (lymphatic marker), podoplanin (lymphatic marker), CD45 (panhematopoietic marker), and DAPI (nuclear marker).

RESULTS

AGs can be classified as intradural or interdural, depending on their location and site of drainage. Interdural AGs are distinct from the dura, adhere to arachnoid membranes, and occasionally open directly in the inferolateral wall or floor of the SSS, although some cross the infradural folds of the dura's inner layer to meet with intradural AGs and IVCs. Intradural AGs are located within the leaflets of the dura. The total number of openings from the AGs, lateral lacunae, and cortical veins into the SSS was 45 ± 5.62 per head. On average each cadaveric head contained 6 ± 1.30 intradural AGs. Some intradural AGs do not directly open into the SSS and use IVCs to connect to the venous circulation. Using immunostaining methods, the authors demonstrate that these tubular channels stain positively with vascular and lymphatic markers (Lyve-1, podoplanin).

CONCLUSIONS

AGs consist of two subtypes with differing modes of drainage into the SSS. A subset of AGs located intradurally use tubular channels, which stain positively with vascular and lymphatic markers to connect to the venous lacunae and ultimately to the SSS. The present study suggests that AGs may function as a component of brain lymphatics. This finding has important clinical implications for cancer metastasis to and from the CNS and may shed light on mechanisms of altered clearance of macromolecules in the setting of neurodegenerative diseases.

Common Challenges and Solutions Associated with the Preparation of Silicone-Injected Human Head and Neck Vessels for Anatomical Study

Neuroanatomy laboratory training is crucial for the education of neurosurgery residents and medical students. Since the brain is a complex and three-dimensional structure, it is challenging to understand the anatomical relationship of the cortex, internal structures, arteries, and veins without appropriate adjuncts. Several injection agents—including the inks/dyes, latex, polyester, acrylic resins, phenol, polyethylene glycol, and phenoxyethanol—have been explored. Colored silicon injection protocols for the head and neck vessels’ perfusion have greatly aided the study of neuroanatomy and surgical planning. This report presents a colored silicone injection method in detail, and also highlights the technical shortcomings of the standard techniques and workarounds for common challenges during 35 human cadaveric head injections. The human cadaveric head preparation and the coloring of the head vessels are divided into decapitation, tissue fixation with 10% formalin, the placement of the Silastic tubing into the parent vessels, the cleaning of the vessels from clots, and the injection of the colored silicone into the vessels. We describe the technical details of the preparation, injection, and preservation of cadaveric heads, and outline common challenges during colored silicone injection, which include the dislocation of the Silastic tubing during the injection, the injection of the wrong or inappropriate colored silicone into the vessel, intracranial vessel perforation, the incomplete silicone casting of the vessel, and silicone leakage from small vessels in the neck. Solutions to these common challenges are provided. Ethyl alcohol fixed, colored human heads provided the long-term preservation of tissue, and improve the sample consistency and preservation for the teaching of neuroanatomy and surgical technique.

Anatomical Features of the Deep Cervical Lymphatic System and Intrajugular Lymphatic Vessels in Humans

BACKGROUND

Studies in rodents have re-kindled interest in the study of lymphatics in the central nervous system. Animal studies have demonstrated that there is a connection between the subarachnoid space and deep cervical lymph nodes (DCLNs) through dural lymphatic vessels located in the skull base and the parasagittal area.

OBJECTIVE

To describe the connection of the DCLNs and lymphatic tributaries with the intracranial space through the jugular foramen, and to address the anatomical features and variations of the DCLNs and associated lymphatic channels in the neck.

METHODS

Twelve formalin-fixed human head and neck specimens were studied. Samples from the dura of the wall of the jugular foramen were obtained from two fresh human cadavers during rapid autopsy. The samples were immunostained with podoplanin and CD45 to highlight lymphatic channels and immune cells, respectively.

RESULTS

The mean number of nodes for DCLNs was 6.91 ± 0.58 on both sides. The mean node length was 10.1 ± 5.13 mm, the mean width was 7.03 ± 1.9 mm, and the mean thickness was 4 ± 1.04 mm. Immunohistochemical staining from rapid autopsy samples demonstrated that lymphatic vessels pass from the intracranial compartment into the neck through the meninges at the jugular foramen, through tributaries that can be called intrajugular lymphatic vessels.

CONCLUSIONS

The anatomical features of the DCLNs and their connections with intracranial lymphatic structures through the jugular foramen represent an important possible route for the spread of cancers to and from the central nervous system; therefore, it is essential to have an in-depth understanding of the anatomy of these lymphatic structures and their variations.

Quantitative comparison of endoscopically assisted endonasal, sublabial and transorbital transmaxillary approaches to the anterolateral skull base

OBJECTIVES

The aim of this anatomical study is to make quantitative comparison among three endoscopic approaches, encompassing contralateral endonasal transseptal transmaxillary transpterygoid approach (contralateral EEA), endoscopic sublabial transmaxillary transalisphenoid (Caldwell-Luc) approach and endoscopic transorbital transmaxillary approach through inferior orbital fissure (ETOA), to the anterolateral skull base for assisting preoperative planning.

DESIGN & PARTICIPANTS

Anatomical dissections were performed in four adult cadaveric heads bilaterally using three endoscopic transmaxillary approaches described above.

SETTING

Skull Base Laboratory at the National Defense Medical Center.

MAIN OUTCOME MEASURES

The area of exposure, angles of attack and depth of surgical corridor of each approach were measured and obtained for statistical comparison.

RESULTS

The ETOA had significantly larger exposure over middle cranial fossa (731.40 ± 80.08 mm² ) than contralateral EEA (266.60 ± 46.74 mm² ) and Caldwell-Luc approach (468.40 ± 59.67 mm² ). In comparison with contralateral EEA and Caldwell-Luc approach, the ETOA offered significantly greater angles of attack and shorter depth of surgical corridor (P < .05 for all comparisons).

CONCLUSIONS

The ETOA is the superior choice for target lesion occupying multiple compartments with its epicentre located in the middle cranial fossa or superior portion of infratemporal fossa.

Endoscopic transorbital approach to anterolateral skull base through inferior orbital fissure: a cadaveric study

BACKGROUND

Endoscopic transorbital approach (eTOA) has been announced as an alternative minimally invasive surgery to skull base. Owing to the inferior orbital fissure (IOF) connecting the orbit with surrounding pterygopalatine fossa (PPF), infratemporal fossa (ITF), and temporal fossa, the idea of eTOA to anterolateral skull base through IOF is postulated. The aim of this study is to access its practical feasibility.

METHODS

Anatomical dissections were performed in five human cadaveric heads (10 sides) using 0-degree and 30-degree endoscopes. A stepwise description of eTOA to anterolateral skull base through IOF was documented. The anterosuperior corner of the maxillary sinus in the horizontal plane of the upper edge of zygomatic arch was defined as reference point (RP). The distances between the RP to the foramen rotundum (FR), foramen ovale (FO), and Gasserian ganglion (GG) were measured. The exposed area of anterolateral skull base in the coronal plane of the posterior wall of the maxillary sinus was quantified.

RESULTS

The surgical procedure consisted of six steps: (1) lateral canthotomy with cantholysis and preseptal lower eyelid approach with periorbita dissection; (2) drilling of the ocular surface of greater sphenoid wing and lateral orbital rim osteotomy; (3) entry into the maxillary sinus and exposure of PPF and ITF; (4) mobilization of infraorbital nerve with drilling of the infratemporal surface of the greater sphenoid wing and pterygoid process; (5) exposure of middle cranial fossa, Meckel's cave, and lateral wall of cavernous sinus; and (6) reconstruction of orbital floor and lateral orbital rim. The distances measured were as follows: RP-FR = 45.0 ± 1.9 mm, RP-FO = 55.7 ± 0.5 mm, and RP-GG = 61.0 ± 1.6 mm. In comparison with the horizontal portion of greater sphenoid wing, the superior and inferior axes of the exposed area were 22.3 ± 2.1 mm and 20.5 ± 1.8 mm, respectively. With reference to the FR, the medial and lateral axes of the exposed area were 11.6 ± 1.1 mm and 15.8 ± 1.6 mm, respectively.

CONCLUSIONS

The eTOA through IOF can be used as a minimally invasive surgery to access whole anterolateral skull base. It provides a possible resolution to target lesion involving multiple compartments of anterolateral skull base.

Renal Cell Carcinoma with Primary Presentation via Metastasis to the Trigeminal Ganglion

BACKGROUND

Renal cell carcinoma (RCC) accounts for ∼8% of all brain metastatic disease; however, spread to the cranial nerves and their ganglia is uncommon. To the best of our knowledge, we report the first case of RCC metastatic to Meckel's cave, which was diagnosed secondary to new trigeminal sensory loss.

METHODS

A 45-year-old man had presented with acute-onset right V3 numbness. Magnetic resonance imaging demonstrated contrast enhancement of the ipsilateral V3, extending from its root at the Gasserian ganglion to the foramen ovale.

RESULTS

He elected for observation, and his symptoms resolved over several weeks. At the scheduled, routine 3-month follow-up examination, he reported symptomatic relapse with new concomitant hyperesthetic/neuropathic pain. Magnetic resonance imaging demonstrated interval enlargement of the enhancing lesion in an atypical pattern, potentially consistent with trigeminal schwannoma versus meningioma, and operative resection was recommended.

CONCLUSION

We have reported a case of RCC presenting with numbness via metastatic spread to Meckel's cave. Although uncommon, metastasis is an important diagnostic consideration for enhancing cranial nerve lesions. Our case has demonstrated that, although a history of malignancy, multiple lesions, or systemic/constitutional symptoms are typical, rare cases can demonstrate isolated central nervous system findings. Thus, short-term radiographic surveillance is indicated if the diagnosis of an intracranial or cranial nerve mass lesion is equivocal.

Neuroendoscopic Resection of Trigeminal Schwannoma in the Pterygopalatine/Infratemporal Fossa via the Transnasal Perpendicular Plate Palatine Bone or Transnasal Maxillary Sinus Approach

BACKGROUND

Both the pterygopalatine fossa (PPF) and the infratemporal fossa (ITF) lie outside the midline of the skull base. Lesions in the PPF or ITF include trigeminal schwannoma (trigeminal schwannoma, TS), which originates from the second or third branch of the trigeminal nerve (maxillary nerve or mandibular nerve). Due to their typically deep anatomic location, lesions in the PPF or ITF can be difficult to treat using traditional surgical approaches. In recent years, because of their advantages, which include the fact that they allow the problem to be observed close up, neuroendoscopic techniques are increasingly being applied in skull base surgery, especially in treatment of lesions around the midline of the base of the skull. This study aims to 1) evaluate the neuroendoscopic treatment of lesions in PPF or ITF via the transnasal palate bone perpendicular plate or transnasal maxillary sinus approach and 2) analyze the clinical significance of this approach.

METHODS

We retrospectively analyzed 3 cases of PPF TSs and 1 case of ITF TS treated between January 2015 and May 2017. All of the cases underwent neuroendoscopic resection of TSs located in the PPF via the nasal perpendicular plate palatine bone (or nasal maxillary sinus) approach.

RESULTS

Two cases of PPF TSs were characterized by a thin palate bone perpendicular plate due to oppressed absorption of the tumor. Therefore the endoscopic transnasal palate bone perpendicular plate approach was employed. Additionally, 1 case of PPF TSs and 1 case of ITF TS were resected via the transnasal maxillary sinus approach. All 4 patients received total resection under endoscopy and recovered well after their respective operations without cerebrospinal fluid leakage, although 1 patient experienced postoperative dry eye symptoms and 1 other patient showed no improvement in facial numbness before and after the operation.

CONCLUSIONS

Neuroendoscopic surgery performed via the transnasal perpendicular plate palatine bone or transnasal maxillary sinus approach has its own unique advantages in removing TSs in PPF and in ITF: Notably, the tumor can be exposed and dealt with under direct vision, which prevents damage to important structures, such as the internal carotid and maxillary nerves, while at the same time helping to achieve total removal of TSs. Furthermore, by adopting this approach versus traditional skull base surgery, postoperative trauma can be reduced significantly, which should be advocated for in this time of minimal invasive surgery.