A novel simple real-time electrooculographic monitoring system during transsphenoidal surgeries to prevent postoperative extraocular motor nerve dysfunction

Management Approaches and Patient Outcomes for Giant Pituitary Neuroendocrine Tumors Classified as Knosp Grade 3 and 4

Background Treatment of patients with a giant pituitary neuroendocrine tumor (GPitNET) is challenging. Here, we present the methods used for the clinical management of patients who underwent GPitNET resection mainly via endoscopic endonasal surgery along with multimodal support to avoid surgical complications, which can affect the outcomes. Methodology The medical records of 25 patients with a GPitNET who underwent endonasal endoscopic surgery were retrospectively reviewed. Complications were analyzed and factors affecting the extent of resection were evaluated. Results Gross total resection was achieved in six (24%), near-total resection (>90%) in nine (36%), and partial resection in 10 (40%) patients. Multivariate analyses revealed that tumors invading the middle fossa had negative effects on the extent of resection (odds ratio = 0.092, p = 0.047). Postoperative vision improved or normalized in 16 (64%), remained stable in eight (32%), and worsened in one (4%), while a new hormonal deficit was noted in seven (28%) patients. Complications included permanent oculomotor nerve palsy in one (4%) and transient oculomotor palsy in one (4%), apoplexy of the residual tumor resulting in ischemic stroke in one (4%), postoperative cerebrospinal fluid leakage in one (4%), and permanent diabetes insipidus in six (24%) patients. Conclusions For GPitNETs that extend into the middle fossa, our study underscored the difficulties in surgical extraction and the necessity for tailored treatment approaches. To ensure the safest and most complete removal possible, the surgical strategy must be specifically adapted to each case. Additionally, employing a comprehensive support approach is essential to reduce the chance of complications in patients impacted by this condition.

Clinical Features of Pituitary or Parasellar Tumor Onset with Cranial Nerve Palsy: Surgical Intervention Considerations

OBJECTIVE

This study aimed to clarify the symptoms of pituitary or parasellar tumor onset with cranial nerve palsy (CNP) and to improve our knowledge of this rare symptom and its most appropriate treatment.

METHODS

Among 1281 patients with pituitary or parasellar tumors surgically treated from 2003 to 2020, 30 cases (2.34%; 15 men and 15 women; mean age: 55.6 years, range: 6-83 years) first presenting with CNP were reviewed to evaluate the neurological symptoms, histological diagnosis, interval from onset to surgery, and time before complete CNP recovery.

RESULTS

Pathological diagnoses comprised 17 pituitary adenomas, including 10 pituitary apoplexies and 4 adrenocorticotropic hormone-positive adenomas, and 13 other tumors, including 3 chordomas, 2 xanthogranulomas, 2 malignant lymphomas, 2 metastatic tumors, 1 Rathke cleft cyst, 1 plasmacytoma, 1 craniopharyngioma, and 1 neuroendocrine carcinoma. The mechanisms causing CNP were pituitary apoplexy (n = 10), cranial nerve compression or involvement (n = 17), and inflammatory changes (n = 9). As the first manifestation, 20 (66.7%) patients presented with oculomotor nerve palsy, 2 (6.7%) with trochlear nerve palsy, and 13 (43.3%) with abducens nerve palsy. Full recovery of CNP was obtained in 25 patients (83.3%) after surgery alone and in 2 patients (6.7%) after adjuvant therapy. Early surgery provided no significant difference in full recovery rates although it reduced the time to reach full recovery.

CONCLUSIONS

It is critical to determine the mechanisms of CNP and intervene surgically to improve symptoms, shorten the duration of the disorder, prevent relapses, and obtain the correct pathological diagnosis to select the proper adjuvant therapy.

Intraoperative lateral rectus electromyographic recordings optimized by deep intraorbital needle electrodes

OBJECTIVE

We demonstrate the advantages and safety of long, intraorbitally-placed needle electrodes, compared to standard-length subdermal electrodes, when recording lateral rectus electromyography (EMG) during intracranial surgeries.

METHODS

Insulated 25 mm and uninsulated 13 mm needle electrodes, aimed at the lateral rectus muscle, were placed in parallel during 10 intracranial surgeries, examining spontaneous and stimulation-induced EMG activities. Postoperative complications in these patients were reviewed, alongside additional patients who underwent long electrode placement in the lateral rectus.

RESULTS

In 40 stimulation-induced recordings from 10 patients, the 25 mm electrodes recorded 6- to 26-fold greater amplitude EMG waveforms than the 13 mm electrodes. The 13 mm electrodes detected greater unwanted volume conduction upon facial nerve stimulation, typically exceeding the amplitude of abducens nerve stimulation. Except for one case with lateral canthus ecchymosis, no clinical or radiographic complications occurred in 36 patients (41 lateral rectus muscles) following needle placement.

CONCLUSIONS

Intramuscular recordings from long electrode in the lateral rectus offers more reliable EMG monitoring than 13 mm needles, with excellent discrimination between abducens and facial nerve stimulations, and without significant complications from needle placement.

SIGNIFICANCE

Long intramuscular electrode within the orbit for lateral rectus EMG recording is practical and reliable for abducens nerve monitoring.

Triggered Electrooculography for Identification of Oculomotor and Abducens Nerves during Skull Base Surgery

OBJECTIVE

Electrooculography (EOG) records eyeball movements as changes in the potential difference between the negatively charged retina and the positively charged cornea. We aimed to investigate whether reliable EOG waveforms can be evoked by electrical stimulation of the oculomotor and abducens nerves during skull base surgery.

METHODS

We retrospectively reviewed the records of 18 patients who had undergone a skull base tumor surgery using EOG (11 craniotomies and seven endonasal endoscopic surgeries). Stimulation was performed at 5 Hz with a stimulus duration of 200 μs and an intensity of 0.1-5 mA using a concentric bipolar probe. Recording electrodes were placed on the upper (active) and lower (reference) eyelids, and on the outer corners of both eyes; the active electrode was placed on the contralateral side.

RESULTS

Reproducibly triggered EOG waveforms were observed in all cases. Electrical stimulation of cranial nerves (CNs) III and VI elicited positive waveforms and negative waveforms, respectively, in the horizontal recording. The median latencies were 3.1 and 0.5 ms for craniotomies and endonasal endoscopic surgeries, respectively (p=0.007). Additionally, the median amplitudes were 33.7 and 46.4 μV for craniotomies and endonasal endoscopic surgeries, respectively (p=0.40).

CONCLUSION

This study showed reliably triggered EOG waveforms with stimulation of CNs III and VI during skull base surgery. The latency was different according to the point of stimulation and thus predictable. As EOG is noninvasive and relatively easy to perform, it can be used to identify the ocular motor nerves during surgeries as an alternative of electromyography.

Endoscopic Endonasal Transpituitary Gland Approach for Resection of Dorsum Sellae Meningioma - Technical Case Report

BACKGROUND AND IMPORTANCE

Access to a dorsum sellae meningioma is difficult. A transcranial approach, such as a pterional, subtemporal, or transpetrosal method, often requires significant brain retraction and crossing of cranial nerves to access this region. We present here a successful purely endoscopic endonasal transpituitary gland approach for resection of a growing dorsum sellae meningioma.

CLINICAL PRESENTATION

A 74-yr-old woman came to us with dizziness. Magnetic resonance imaging (MRI) demonstrated a mass on the dorsum sellae around the left posterior clinoid. Follow-up MRI examinations over a 3-yr period showed a gradual increase in size of the mass and increasing compression of the left peduncle. To avoid brain retraction, an endoscopic endonasal approach was selected for tumor removal. With this method, we went through the pituitary gland by splitting it, and drilled into the dorsum sellae and clivus to access the front of the tumor. Gross total removal was safely achieved. The patient was asymptomatic and had normal pituitary function after the operation.

CONCLUSION

The present endoscopic endonasal transpituitary gland approach allowed for safe resection of a dorsum sellae meningioma. We consider it to be less invasive for patients because of no need for brain retraction.

A novel needle electrode for intraoperative fourth cranial nerve neurophysiological mapping

OBJECTIVES

Trochlear nerve (CN-IV) mapping method has not been confirmed to date. The compound muscle action potential (CMAP) of CN-IV cannot be recorded because of the low mapping sensitivity and anatomical characteristics of the superior oblique muscle (SOM). The aim of this study was to evaluate the effectiveness of a novel needle electrode (NNE), for the intraoperative mapping of CN-IV.

MATERIALS AND METHODS

The NNEs were inserted in the target extraocular muscles in 19 patients. We compared the CMAP amplitude of the NNE with that of the conventional needle electrode (CNE). Furthermore, we investigated the dissimilarity between the CMAP of the CN-IV and other extraocular cranial nerves (ECNs) and the correlation between the readings of the CN-IV mapping and its postoperative functional outcome.

RESULTS

The CMAP of CN-IV has been measured in nine patients (47.4%). The CMAP of CN-IV was distinguishable from other ECNs. The CMAP of the NNE was found to be three times higher than that of the CNE. Although the NNE has shown the potential to record the CN-IV's CMAP, 4 cases ended up having a CN-IV postoperative dysfunction.

CONCLUSIONS

For the first time, we confirmed the possibility of intraoperative mapping the CN-IV using an NNE inserted into the SOM. The NNE can also be useful for other neurophysiological monitoring methods.

Novel method of intraoperative ocular movement monitoring using a piezoelectric device: experimental study of ocular motor nerve activating piezoelectric potentials (OMNAPP) and clinical application for skull base surgeries

Intraoperative monitoring systems that utilize various evoked potentials for the detection and/or preservation of cranial nerves have become increasingly common due to recent technical and commercial developments, particularly during skull base surgeries. We established a novel system for the intraoperative monitoring of the extraocular motor nerves (eOMNs) using a piezoelectric device capable of detecting imperceptible vibrations induced by ocular movement, with sensors placed on the eyelids alone. We first evaluated the efficacy and reliability of this device for the intraoperative monitoring of eOMNs in two Beagle dogs. Based on the results, we then determined the appropriate stimulation parameters for use in human surgical cases involving removal of various skull base tumors. Animal experiments revealed that a 0.4 mA monopolar electrical stimulation was required to elicit significant responses and that these responses were not inferior to those obtained via the electrooculogram/electromyogram. Significant responses were also detected in preliminary clinical investigations in human patients, following both direct and indirect monopolar electrical stimulation of the oculomotor and abducens nerves, although obtaining responses from the trochlear nerve was difficult. Intraoperative monitoring using a piezoelectric device provides a simple and reliable method for detecting eOMNs, especially the oculomotor and abducens nerves. This monitoring system can be adapted to various surgeries for skull base tumor.

Electrophysiology of Extraocular Cranial Nerves: Oculomotor, Trochlear, and Abducens Nerve

The utility of extraocular cranial nerve electrophysiologic recordings lies primarily in the operating room during skull base surgeries. Surgical manipulation during skull base surgeries poses a risk of injury to multiple cranial nerves, including those innervating extraocular muscles. Because tumors distort normal anatomic relationships, it becomes particularly challenging to identify cranial nerve structures. Studies have reported the benefits of using intraoperative spontaneous electromyographic recordings and compound muscle action potentials evoked by electrical stimulation in preventing postoperative neurologic deficits. Apart from surgical applications, electromyography of extraocular muscles has also been used to guide botulinum toxin injections in patients with strabismus and as an adjuvant diagnostic test in myasthenia gravis. In this article, we briefly review the rationale, current available techniques to monitor extraocular cranial nerves, technical difficulties, clinical and surgical applications, as well as future directions for research.

Usefulness of intraoperative electromyographic monitoring of oculomotor and abducens nerves during skull base surgery

BACKGROUND

Intraoperative neurophysiologic monitoring of the extraocular cranial nerve (EOCN) is not commonly performed because of technical difficulty and risk, reliability of the result and predictability of the postoperative function of the EOCN.

METHODS

We performed oculomotor nerve (CN III) and abducens nerve (CN VI) intraoperative monitoring in patients with skull base surgery by recording the spontaneous muscle activity (SMA) and compound muscle action potential (CMAP). Two types of needle electrodes of different length were percutaneously inserted into the extraocular muscles with the free-hand technique. We studied the relationships between the SMA and CMAP and postoperative function of CN III and CN VI.

RESULTS

A total of 23 patients were included. Nineteen oculomotor nerves and 22 abducens nerves were monitored during surgery, respectively. Neurotonic discharge had a positive predictive value of less than 50% and negative predictive value of more than 80% for postoperative CN III and CN VI dysfunction. The latency of patients with postoperative CN III dysfunction was 2.79 ± 0.13 ms, longer than that with intact CN III function (1.73 ± 0.11 ms). One patient had transient CN VI dysfunction, whose CMAP latency (2.54 ms) was longer than that of intact CN VI function (2.11 ± 0.38 ms). There was no statistically significant difference between patients with paresis and with intact function.

CONCLUSIONS

The method of intraoperative monitoring of EOCNs described here is safe and useful to record responses of SMA and CMAP. Neurotonic discharge seems to have limited value in predicting the postoperative function of CN III and CN VI. The onset latency of CMAP longer than 2.5 ms after tumor removal is probably relevant to postoperative CN III and CN VI dysfunction. However, a definite quantitative relationship has not been found between the amplitude and stimulation intensity of CMAP and the postoperative outcome of CN III and CN VI.

Surgical Anatomy for the Endoscopic Endonasal Approach to the Ventrolateral Skull Base

The authors describe the surgical anatomy for the endoscopic endonasal approach (EEA) to the ventrolateral skull base. The ventrolateral skull base can be divided into two segments: the upper lateral and lower lateral skull base. The upper lateral skull base includes the cavernous sinus and the orbit, while the lower lateral skull base includes the petrous apex, Meckel's cave, parapharyngeal space, infratemporal fossa, etc. To gain access to the upper lateral skull base, a simple opening of the ethmoid sinus provides sufficient exposure of this area. To reach the lower lateral skull base, a transpterygoid approach, following ethmoidectomy, is a key procedure providing wide exposure of this area. Understanding of surgical anatomy is mandatory for treating ventrolateral skull base lesions via EEA. An appropriate, less-invasive approach should be applied depending on the size, location, and type of lesion.

Intra-operative electrooculographic monitoring to prevent post-operative extraocular motor nerve dysfunction during skull base surgeries

BACKGROUND AND AIMS

Intra-operative identification and preservation of extraocular motor nerves is one of the main goals of surgeries for skull base tumours and this is done by monitoring the extraocular movement (EOM). Intra-operative electromyographic monitoring has been reported, but it is a complex and skilful process. Electrooculography (EOG) is a simple and reliable technique for monitoring EOMs. We aimed to assess the utility of EOG monitoring in preventing extraocular motor nerve dysfunction during skull base surgeries.

METHODS

In this retrospective cohort study, intra-operative EOG recordings were obtained using disposable needle electrodes placed on the periorbital skin and the polarity of the waves noted for interpretation. Triggered as well as continuous EOG responses were recorded after monopolar electrode stimulation of cranial nerve (CN) during tumour removal which helped the surgeon with careful dissection and avoiding potential nerve injuries.

RESULTS

Of the 11 cases monitored, oculomotor and abducent nerves were identified in all cases, but the trochlear nerve could not be definitively identified. Six patients had no pre- or post-operative extraocular motor nerve dysfunction. The other five patients had pre-existing deficits before surgery, which recovered completely in two, significantly in one, and did not improve in two patients at 3-6 months follow-up.

CONCLUSIONS

EOG was found to be a simple and reliable method of monitoring extraocular motor nerves (CNs III and VI) intraoperatively.