ETV is a popular standard treatment for obstructive hydrocephalus. It is the first-line approach in cases of aqueductal stenosis, with a success rate above 60%. ETV is equally effective in treating hydrocephalus due to tectal plate lesions8,24). The results of ETV in patients are influenced by hydrocephalus etiology and patient age. Congenital hydrocephalus and that combined with myelomeningocele are not satisfactorily treated in very young children, but success rates are better in older children and adolescents (>70%)8,16).

In patients with midline posterior fossa tumors, preoperative ETV is considered in severe hydrocephalus requiring urgent management. ETV is also suitable for postoperative hydrocephalus as an alternative to shunt insertion16,21).

Use of the endoscope has also been explored for other complicated forms of hydrocephalus. Septostomy or septum pellucidotomy can be performed endoscopically to treat isolated lateral ventricles. Fenestration of loculated ventricles due to various causes can also be performed by endoscopy. Aqueductoplasty was recently reported for the treatment of trapped fourth ventricle syndrome. Applied neuroendoscopic techniques have been extended to foraminoplasty of the foramens of Monro and Magendie, as well as endoscopic fourth ventriculostomy16,19,21).

Endoscopic procedures include cyst fenestration, tumor biopsy, tumor removal, and metastatic disease assessment. Suprasellar or quadrigeminal arachnoid cysts presenting with hydrocephalus are good candidates for endoscopic fenestration. Most patients with intraventricular cyst or tumors have concomitant hydrocephalus. This makes endoscopic surgery particularly advantageous, as simultaneous procedures can be performed for both CSF diversion and tumor management6,7). Endoscopic tumor biopsy is a well-established method for intraventricular brain tumors. It has a high diagnostic yield (>90%) and low risk (<3.5%). Germ cell tumor, infiltrative hypothalamic/optic pathway glioma, and Langerhans cell histiocytosis are addressable with endoscopic biopsy21). Endoscopic removal is suitable for colloid cysts or tumors that are also pedunculated at the ependymal surface. Endoscopic excision of a colloid cyst is technically feasible through the lateral ventricle in most cases unless the cyst is very large, which increases the risk of venous injury at the foramen of Monro21,25). Transventricular endoscopic tumor cyst decompression can temporarily or permanently alleviate obstructive hydrocephalus or visual loss. It can be employed in patients with craniopharyngioma, hypothalamic/chiasmatic astrocytoma, and suprasellar or pineal germ cell tumors. Total removal of the solid tumor is limited due to the inadequacy of compatible endoscopic instrumentation and limited bleeding control. The success of endoscopic tumor removal depends on tumor size, density, and vascularity21,25). Extraventricular arachnoid cyst located at the sylvian fissure or interhemispheric fissure and posterior fossa can be treated with endoscopic approaches. Endoscopic fenestration can be safely performed from inside of the cyst into the surrounding subarachnoid space6).

HHs are rare non-neoplastic congenital malformations arising from the inferior hypothalamus and associated with gelastic seizures, precocious puberty, and cognitive problems. All patients except those with precocious puberty require surgical treatment. Single or combination treatment should be used according to HH type (classified by Delalande and Fohlen5) or Choi et al.2,3)). The transcallosal craniotomy approach is preferred for large HHs. Gamma knife surgery is an option for small lesions. Stereotactic radiofrequency thermocoagulation has been safely applied for small- or medium-sized HHs with good short-term results. Endoscopic resection assisted with stereotactic navigation has been attempted to surgically remove small HHs, but parts of the tumors remained. Surgeries to resect HHs are typically performed in multiple steps. Nevertheless, recent reports indicate that endoscopic disconnection of HHs seems to be safer and more effective than other modalities3,20). In most cases, navigation assistance is recommended because lateral and third ventricles are normal sizes in these patients.

Neuroendoscopy for skull base tumors began with Carrau and colleagues1), who reported their original experience of endonasal transsphenoidal hypophysectomy at the University of Pittsburgh. de Divitiis and colleagues4) expanded the scope of this approach to include other lesions of the sellar and parasellar regions. The bilateral endonasal endoscopic approach now allows for visualization of tumors at the anterior skull base up to the crista galli and down to the level of C2. The endoscopic endonasal technique has been applied for surgical excision of pituitary adenoma and craniopharyngioma with encouraging results and low morbidity. The route of the endoscopic approach for sellar or suprasellar tumors should be based on the extent of lesion. Supradiaphragmatic lesions can be removed via the endonasal route, and suprasellar prechiasmatic preinfundibular lesions can be removed with the transtuberculum-transplanum sphenoidale approach21).

Endoscopic treatment has been applied for the treatment of CSF rhinorrhea, which commonly occurs as the result of trauma and iatrogenic disruption of the skull base and secondary to inflammatory, neoplastic, and pseudotumor syndromes. Skull base defects can be repaired with endoscopic remodeling of tissue planes and complete separation of the cranial space and sinonasal cavities to perform a multilayered reconstruction. Small bony defects can be closed with a single layer of autologous fat or fascia, followed by tissue sealant. Larger skull base defects with a high-volume intraoperative CSF leaks require multilayered closure. This can be achieved with an autologous fat graft in the bony defect followed by fascia lata, bony buttress, and tissue sealant. These larger skull base defects can be supplemented with a gasket seal closure21).

Jimenez and colleagues12,13) pioneered minimally invasive surgical treatment of craniosynostosis. This condition can be corrected with endoscopy-assisted craniosynostosis surgery (EACS) before the age of 6 months combined with postoperative helmet molding therapy. The optimal age for EACS is 3 months. The procedure is essentially strip craniectomy and can be performed with a standard armamentarium and a 0° endoscope with a working shaft used for endoscopic facial lift surgery without irrigation. The authors reported a low complication rate and good success rate. A separate aspirator parallel to the endoscope is used for blood aspiration.

In scaphocephaly, the craniectomy is performed from the anterior to the posterior fontanelle. The bone is cut with strong scissors. The removed strip should be 4–5 cm wide and 11 cm long. Lateral barrel stave osteotomies or wedge-shaped osteotomies can be added behind the coronal suture and in front of the lambdoid sutures. This endoscopic approach has a low reported complication rate and good success rate. Furthermore, only 9% of 139 patients required blood transfusion in their most recent publication. The children wear a helmet within 3 weeks postoperatively for 10 months. Special attention is paid for possible pressure ulcerations or eczema, but skin complications are rare12,13,21).

In the last decade, the neuroendoscope has been increasingly used in the surgical management of both intra- and extradural spinal diseases. Fenestration of intradural arachnoid cysts can be easily performed with the endoscope. In the 1990s, it was popular to dissect the septations of multiloculated syringomyelia cavities, but their clinical and radiological benefits were limited11).

The neuroendoscope is an important part of the minimally invasive spine surgery movement. Endoscopic approaches have expanded to thoracoscopic sympathectomy, discectomies, lumbar laminotomies, anterior approaches for spinal reconstruction, and resection of tumors and cysts. Endoscopic discectomy is increasingly performed in both the thoracic and lumbar regions. Epiduroscopy is used in patients who have peridural fibrosis following spinal procedures, but its success and usefulness must be followed up further10,21).

Improved illumination and vision of endoscopes has led to the possibility of working in the brain parenchyma. The concept of a keyhole craniotomy combined with a selected trajectory enables the endoscopic approach of intraparenchymal lesions with an assisted navigation system. Endoscopic resection is then performed by introducing instruments through the sheath, and various instruments such as suction tubes, tumor forceps, microscissors, and monopolar or bipolar coagulation can be used for lesion resection. To ensure efficient operation under a good endoscopic view, it is very important to maintain good intraoperative irrigation and drainage21).

Partial or total lesion removal may be achieved depending on the nature of tumor. Selected cases for this endoscopic surgery remain limited but include cavernous angiomas, intraparenchymal hematomas, cerebellar infarctions, and brain abscesses. This technique was demonstrated to be accurate and safe and possibly will be expanded to remove other intraparenchymal lesions in the future21).

Many neurosurgeons have recently used the neuroendoscope to assist with “traditional” skull base microsurgery. The endoscope has already been reported as a useful adjunct to the microscope in anterior skull base surgeries, posterior fossa approaches, and aneurysm surgery. The microscopic approach makes dissected structures visible in a straight line with the great advantages of high resolution, excellent color fidelity, and stereoscopic vision. For working “around a corner,” the endoscope is applied to reduce retraction and skull base drilling.

In endoscope-assisted microsurgery, most of the procedure is performed under a microscopic view because of the better image quality. However, endoscopic approaches are used in certain steps. The endoscope is mostly used to look around bony or dural corners, as well as neurovascular structures, to avoid retraction and extensive skull base drilling. Frequently, the endoscope is simply used freehand for inspection. However, when bimanual dissection is required, the endoscope is fixed to a self-retaining holding device, and the surgeon has both hands free for manipulation1,4,21).

The endoscope-assisted technique has proven useful in skull base surgery for tumors (pituitary tumor, craniopharyngioma, acoustic neuroma, epidermoid), aneurysm clipping, and trigeminal microvascular decompression21).