Endoscopic endonasal surgical anatomy of the optic canal: key anatomical relationships between the optic nerve and ophthalmic artery.

PURPOSE: A detailed understanding of the neurovascular relationships between the optic nerve (ON) and the ophthalmic artery (OA) in the optic canal (OC) is paramount for safe surgery. We focused on the neurovascular anatomy of this area from both an endoscopic endonasal and transcranial trajectories to compare the surgical exposures and perspectives offered by these different views and provide recommendations to increase the intraoperative safety. METHODS: Twenty sides of ten formalin-fixed, latex-injected head specimens were utilized. The surgical anatomy and anatomical relationships of the OA in relationship to the ON along their intracranial and intracanalicular segments was studied from endoscopic endonasal and transcranial perspectives. RESULTS: Three types of OA-ON relationships at the origin of the OA were identified: inferomedial (type 1, 35%), inferior (type 2, 55%), and inferolateral (type 3, 10%). The endoscopic endonasal trajectory offers an inferomedial perspective of the ON-OA neurovascular complex, in which the OA, especially when located inferomedially, is first encountered. When comparing with the transcranial view, all OA were covered by the nerve, type 1 was located below the medial third, type 2 below the middle third, and type 3 below the lateral third of the OC. The mean extension of the intracanalicular portion of both OA and ON was 8.9 mm, while the intracranial portion of the OA and ON were 9.3 mm and 12.4 mm, respectively. The OA, endoscopically, is located within the inferior half of the OC, and occupies 39%, 43%, and 42% of the OC height at its origin, mid, and end points, respectively. The mean distance between the superior margin of the OC at its origin and superior margin of the OA is 1.4 mm. CONCLUSIONS: Detailed anatomical understanding of the OC, and the ON and OA at their intracranial and intracanalicular segments is paramount to safe surgery. When opening the OC dura endoscopically, our results suggest that a medial incision along the superior third of the OC with a proximal to distal direction is recommended to avoid injury of the OA.

Racial, Ethnic, and Gender Variations in Sinonasal Anatomy.

BACKGROUND: Complications during endoscopic sinus surgery often result from unfavorable anatomy. The prevalence rates of such anatomic findings vary tremendously in the literature, in part due to the small, homogenous populations previously studied. OBJECTIVE: To characterize the prevalence of sinonasal anatomic variants among ethnic groups and genders seen at an academic medical center. METHODS: This is a retrospective cross-sectional study of adult subjects who underwent CT imaging of the sinuses from January 2019 to November 2020 at a tertiary academic setting. CT scans were analyzed systematically by 3 trained study personnel for the presence of critical sinus anatomic variants that endoscopic sinus surgeons typically evaluate for preoperatively. Chi-squared tests and analyses of variance were conducted to detect differences in the prevalence of structural findings between genders and races/ethnicities. RESULTS: A total of 489 subjects (57% female) were included: 44 Asian, 14 Black/African American, 101 Hispanic/Latino, 203 White, 127 Other. The prevalence of the following anatomical variants differed by race/ethnicity: Haller cells, Type 3 optic nerve, Onodi cells, maxillary septations, sphenoid lateral recess, anterior clinoid process pneumatization, and carotid artery dehiscence. Asian subjects had higher rates of Haller cells (48% vs 16%, P < .001) and Type 3 optic nerve (18% vs 4%, P = .022) compared to Hispanic subjects, as well as a higher prevalence of Onodi cells (39% vs 17%, P = .003) compared to White subjects. Males had a higher prevalence of mesenteric anterior ethmoid arteries (62% vs 45%, P < .001) and dehiscent carotid arteries (30% vs 21%, P = .024). CONCLUSION: Certain sinonasal anatomic variants, which have direct implications for complications during endoscopic sinus surgery, were found to be significantly more prevalent in some demographic groups. Surgeons should be aware of these differences in their review of preoperative imaging for safe surgical planning.

Lost or fragmented bony septum of the optic canal facing the sphenoid sinus: a histological study using elderly donated cadavers.

PURPOSE: To histologically describe a direct contact (the so-called dehiscence) of the optic nerve (ON) and/or internal carotid artery (ICA) to the mucosa of posterior paranasal sinuses represented by the sphenoid sinus (SS). METHODS: Observations of histological sections of unilateral or bilateral skull bases (parasellar area and orbital apex) from 22 elderly cadavers were made. RESULTS: A bony septum was less than 300 µm between the SS and ICA and 200 µm between the SS and optic nerve. Parts of the septa were sometimes absent due to fragmentation and holes of the bony lamella (2/22 facing the ICA; 4 facing the ICA in combination with an absent bony septum facing the nerve). In these dehiscence sites, the SS submucosal tissue attached to a thick sheath (50-100 µm in thickness) enclosing the optic nerve and ophthalmic artery and/or the ICA adventitia (50-200 µm in thickness). The ICA sometimes contained a sclerotic plaque that attached to or even protruded into the SS. With or without dehiscence, the SS mucosa was always thin (50-100 µm in thickness) and accompanied no mononuclear cellular infiltration or tumor. CONCLUSIONS: A thin bony septum of the optic nerve or ICA had been notable as a danger point during surgery, but even a 0.05-mm-thick bone lamella might be an effective barrier against cellular infiltration or bacterial invasion from the SS. Fragmentation and holes of the bony lamella in 4 cadavers might allow cellular invasion to the optic nerve. Accordingly, unknown immunological cross talks might occur to cause demyelination.

Orbital lymphatic vessels: immunohistochemical detection in the lacrimal gland, optic nerve, fat tissue, and extrinsic oculomotor muscles / Vasos linfáticos orbitários: identificação imunohistoquímica na glândula lacrimal, no nervo óptico, no tecido adiposo e nos músculos extrínsecos oculomotores

ABSTRACT Purpose: To identify the lymphatic vessels in orbital specimens from human cadavers using light microscopy and immunohistochemical analysis. Methods: A postmortem study included 10 orbital specimens from 10 human cadavers. The orbital specimens were obtained no later than 12 hours after death. The orbital specimens were dissected into lacrimal gland, optic nerve, fat tissue, and oculomotor muscles. The histologic criteria to qualify as a lymphatic vessel were thin-walled channels of endothelium without a well-developed basal membrane and with an erythrocyte-free, irregular lumen. The immunohistochemical criteria were irregularly shaped, thin-walled vessels with an erythrocyte-free, irregular lumen and immunopositivity for podoplanin D2-40. Results: The lacrimal gland, optic nerve, fat tissue, and extraocular muscle sections were positively stained with podoplanin D2-40. Conclusions: This study demonstrated lymphatic vessels in the human orbit, more precisely, in the lacrimal gland, dura mater of the optic nerve, adipose tissue, and extrinsic oculomotor muscles via light microscopy and immunohistochemistry.(AU)

RESUMO Objetivos: Identificar vasos linfáticos em espécimes orbitários de cadáveres humanos através de microscopia óptica e análise imunohistoquímica. Métodos: Um estudo postmortem incluiu dez espécimes orbitários provenientes de dez cadáveres humanos. Todos os espécimes orbitários foram obtidos até 12 horas após a morte com uma técnica cirúrgica de exenteração orbitária e dissecados em glândula lacrimal, nervo óptico, gordura órbitária e músculos extraoculares. Para classificar como um vaso linfático, os critérios histológicos incluíram vasos endoteliais de parede única sem membrana basal bem desenvolvida, irregulares e lúmen sem hemácias, e os critérios imunohistoquímicos incluíram vasos endoteliais de parede única, com formato irregular e lúmen sem hemácias e reagentes a podoplanina D2-40. Resultados: As lâminas histológicas de glândula lacrimal, nervo óptico, tecido adiposo e músculos extraoculares reagiram positivamente a podoplanina D2-40. Conclusão: Este estudo demonstrou vasos linfáticos na órbita humana, mais exatamente, na glândula lacrimal, no nervo óptico, na gordura orbitária e nos músculos extrínsecos extraoculares via microscopia óptica e imunohistoquímica.(AU)

Effects of sevoflurane and propofol on the optic nerve sheath diameter in patients undergoing laparoscopic gynecological surgery: a randomized controlled clinical studies.

BACKGROUND: The results of studies on changes in intracranial pressure in patients undergoing laparoscopic surgery are inconsistent. Meanwhile, previous neurosurgery studies have suggested that propofol and sevoflurane have inconsistent effects on cerebral blood flow and cerebrovascular self-regulation. The purpose of this study is to compare changes in the optic nerve sheath diameter in patients undergoing laparoscopic gynecological surgery under anesthetic maintenance with propofol versus sevoflurane. METHODS: This study included 110 patients undergoing laparoscopic gynecological surgery with an estimated operative time of more than 2 h under general anesthesia. The study was a randomized controlled study. The optic nerve sheath diameter (ONSD) at various time points was measured by ultrasound, including when the patients entered the operating room (Tawake), after successful anesthesia induction and endotracheal intubation (Tinduction), when the body position was adjusted to the Trendelenburg position and the CO2 pneumoperitoneum pressure reached 14 mmHg, which was recorded as T0. Then, measurements were conducted every 15 min for the first 1 h and then once every hour until the end of the surgery (T15, T30, T45, T1h, T2h …), after the end of surgery and the tracheal tube was removed (Tend), and before the patients were transferred to the ward (Tpacu). RESULTS: A significant difference in optic nerve sheath diameter was found between two groups at T15, T30, T45 (4.64 ± 0.48 mm and 4.50 ± 0.29 mm, respectively, p = 0.031;4.77 ± 0.45 mm and 4.62 ± 0.28 mm, respectively, p = 0.036;4.84 ± 0.46 mm and 4.65 ± 0.30 mm, respectively, p = 0.012), while there was no significant difference at Tawake and other time points. CONCLUSION: During laparoscopic gynecological surgery lasting more than 2 h, the optic nerve sheath diameter was slightly larger in the propofol group than that in the sevoflurane group in the first 45 min. No significant difference was observed between the two groups 1 h after surgery. TRIAL REGISTRATION: clinicaltrials.gov, NCT03498235 . Retrospectively registered 1 March 2018. The manuscript adheres to CONSORT guidelines.

The effect of laryngoscope types on hemodynamic response and optic nerve sheath diameter. McCoy, Macintosh, and C-MAC video-laryngoscope.

OBJECTIVES: This study aims to investigate the effect of McCoy, Macintosh laryngoscope, and C-MAC video-laryngoscopes on optic nerve sheath diameter (ONSD) and hemodynamic responses to laryngoscopy and intubation. METHODS: This prospective randomized study was conducted in Zonguldak Bülent Ecevit University Hospital, Zonguldak, Turkey, between July 2019 and January 2020. Informed written consent was obtained from all patients. Patients with previous intracranial/ocular surgery or glaucoma were excluded from the study. The patients were randomized to use McCoy, Macintosh, and C-MAC (30 per group). Intubations were performed by the same person. Mean arterial pressure, heart rate (HR), and ONSD were recorded before the induction and repeated in 1, 3, 5, and 10 minutes after the intubation. RESULTS: The effects of laryngoscopy and intubation on hemodynamic responses and ONSD were similar between groups (p greater than 0.05). While the comparison within groups showed ONSD increase in McCoy group and HR and ONSD increase in the Macintosh group compared to baseline 1 min after the intubation, no change was observed in hemodynamic responses and ONSD measurements in the C-MAC® group (p greater than 0.05). CONCLUSIONS: In this study, there was no significant difference between the groups in terms of ONSD and hemodynamic responses to laryngoscopy and intubation. It was observed that there were no significant changes in ONSD values just in C-MAC® video-laryngoscope group. Therefore, intubations with C-MAC® video-laryngoscope are thought to be more appropriate for patients with an increase in intracranial pressure.

The falciform ligament: Anatomical study with microsurgical implications.

OBJECTIVES: The current study aims to increase awareness of the falciform ligament and its anatomical and surgical relationships, for the benefit of the neurosurgeon. PATINENTS AND METHODS: Twenty-four sides from twelve Caucasian cadaveric heads (all fresh-frozen) were used in this study. The length and thickness of the falciform ligament were recorded. The relationship of the falciform ligament to the optic nerve was also observed and documented. Finally, the force needed to avulse the falciform ligament was recorded. RESULTS: In all specimens, the ligament was identified as a continuation of the outer dural layer, forming a roof at the entrance of the optic canal. The mean medial-to-lateral length, anteroposterior length, and thickness of the falciform ligament were 7.97 mm, 2.12 mm, and 0.26 mm, respectively. The mean distance from the medial attachment of the ligament to the midline was 5.54 mm. For the undersurface of the falciform ligament, the optic nerve occupied the middle third in 50.0 %, the lateral third in 44.4 %, and the medial third in 5.6 % of sides. The mean optic nerve diameter at the entrance of the optic canal was 4.20 mm. The mean failure force was 2.47 N. CONCLUSION: The anatomical measurements and relationships provided in this description of the falciform ligament serve as a tool for surgery selection and planning, as well as an aid to improving microsurgical techniques, with the final goal being better patient outcomes.

Evaluation of the effect of Boyle-Davis mouth gag on intracranial pressure in patients undergoing adenotonsillectomy by using ultrasonographic optic nerve sheath diameter measurement.

OBJECTIVE: We aimed to evaluate the effect of an increase in intracranial pressure (ICP) due to sympatho-adrenergic response caused by mouth gag and tongue depressor during adenotonsillectomy by measuring the optic nerve sheath diameter (ONSD) by ultrasonographic method. METHODS: Forty patients (age range 3-12 years) who underwent adenotonsillectomy were included in the study. All patients underwent surgery under general anesthesia with endotracheal intubation. Boyle-Davis mouth gag was used during the procedure. ONSD measurement was performed and a high-frequency linear probe. All ONSD measurements were performed by a single investigator experienced in the use of ultrasound. Ultrasonographically measured ONSD before induction was accepted as baseline (T0) value. Immediately after insertion of the mouth gag (T1), just before removal of the mouth gag (T2), and just before extubation (T3), ultrasonographic measurements of ONSD were recorded. RESULTS: When patients' baseline ONSD values were compared with the values obtained in T1, T2, T3, and a statistically significant increase was detected. The ONSD value measured before removing the mouth gag (T2) was significantly higher than the ONSD value measured immediately after the insertion of the mouth gag (T1). The ONSD value measured just before extubation (T3) and after removal of the mouth gag was significantly lower than the ONSD value (T2) measured just before removal of the mouth gag. When heart rate, mean arterial pressure (MAP), peripheral oxygen saturation (SpO2) values of T0, T1, T2, T3 were compared, any statistically significant difference was not observed. When end-tidal carbon dioxide level (etCO2) and peak inspiratory pressure (PIP) values of T1, T2, T3 were compared, any statistically significant difference was not observed. CONCLUSION: This study showed that the Boyle-Davis mouth gag used during the adenotonsillectomy operation resulted in a significant increase in the diameter of the optic nerve sheath measured ultrasonographically and increased the ONSD even further during the time the mouth gag was remained in situ. In children with intracranial pathologies who will undergo adenotonsillectomy or those with increased ICP-related risk factors, the risks that may arise from the effect of the Boyle-Davis mouth gag on ICP should be considered.

Effect of neck extension on ultrasonographic optic nerve sheath diameter as a surrogate for intracranial pressure in patients undergoing palatoplasty: A prospective observational study.

Palatoplasty is performed with neck extension in patients with a cleft palate. The neck extension required for a better surgical view during palatoplasty can affect intracranial pressure. We evaluated the effect of neck extension on intracranial pressure by measuring the optic nerve sheath diameter using ultrasonography during palatoplasty. The optic nerve sheath diameter was measured in 30 patients at 10 min after anesthetic induction in the supine position (T1), at 10 min after neck extension before preparing for a sterile field (T2), at the end of surgery with neck extension (T3), and at 10 min after the supine position (T4). Hemodynamic and respiratory variables such as systolic blood pressure, heart rate, end-tidal carbon dioxide partial pressure, and peak airway pressure were also measured at the same time points. In comparison with the optic nerve sheath diameter measured at 10 min after anesthetic induction in the supine position (T1), the mean optic nerve sheath diameters were significantly increased at 10 min after neck extension before preparing for a sterile field (T2), at the end of surgery with neck extension (T3), and at 10 min after the supine position (T4; 4.19 ±â€¯0.26, 5.20 ±â€¯0.29, 4.38 ±â€¯0.36, and 4.35 ±â€¯0.30 mm, respectively). However, hemodynamic and respiratory variables were not significantly different at all time points. We found that the optic nerve sheath diameter, an indicator of intracranial pressure, was increased during palatoplasty with neck extension, which suggests that the position may affect the intracranial pressure of patients with a cleft palate.

Optico-carotid recess and anterior clinoid process pneumatization â€" proposal for a novel classiï¬cation and uniï¬ed terminology: an anatomic and radiologic study.

BACKGROUND: The aims of this study were to propose a novel and uniï¬ed classiï¬cation system of the optico-carotid recess (OCR) and anterior clinoid process (ACP) pneumatization, determine their frequency in a Caucasian population and measure the size of the OCR. METHODOLOGY: A total of 200 specimen (400 sphenoid sinuses) were evaluated in a separate anatomic cadaveric study (n=100) and radiologic study (n=100) by using sphenoidal sinus cast and computed tomography (CT) scan. OCR was divided according to its location to the optic nerve into sub-optical and latero-optical OCR grade I-III. RESULTS: An OCR was found in 39% of the samples (78/200) and in 19% (38/200) it occurred bilaterally. Both, sub-optical and latero-optical OCR were identiï¬ed in 14% of the sides (58/400), with a mean length and depth of 6.9 mm; 7.7 mm and 2.3 mm, 7.1 mm, respectively. We determined the pneumatized ACP frequency with 23% (46/200) and deï¬ned 3 uniï¬ed different types of pneumatization. CONCLUSIONS: The OCR is a reliable landmark to identify the optico-carotid region in endoscopic sphenoid sinus surgery, and can even be visualized by CT. Hence, preoperative investigation of the sphenoid region is mandatory. In our opinion, the classiï¬cation presented in this study can be useful in order to avoid surgical complications.

Completely Dehiscent Posterior Sphenoid Sinus Wall During Endoscopic Pituitary Surgery.

A 53-year-old man presented with a 1-week history of headache and double vision. On examination, he was found to have right cranial nerve III palsy. Computed tomography and magnetic resonance imaging of the brain showed a sellar mass with right cavernous sinus invasion. There was no evidence of anterior visual pathway compression on formal neuro-ophthalmologic examination. An elective endoscopic transsphenoidal adenectomy was performed. On access to the sphenoid sinus, he was noted to have a completely dehiscent posterior bony wall of sphenoid sinus with only a thin mucous membrane covering the sella, optic nerves, carotid arteries, and clivus (Figure 1). A focal area of mucosa was subsequently stripped from the posterior sphenoid sinus wall, and a micro-Doppler was used to localize the carotid arteries before sharp dural opening. The tumor was subsequently resected without complication. Failure to appreciate this uncommon anatomic variant (Figures 2 and 3) could result in disastrous irreversible carotid artery or optic nerve injury.

Effects of positive end-expiratory pressure on intraocular pressure and optic nerve sheath diameter in robot-assisted laparoscopic radical prostatectomy: A randomized, clinical trial.

BACKGROUND: There has been no study of the effect of post end-expiratory pressure (PEEP) on intraocular or intracranial pressure during pneumoperitoneum with steep Trendelenburg positioning. We investigated the effects of 5 cmH2O of PEEP on intraocular pressure and optic nerve sheath diameter as a surrogate for intracranial pressure in robot-assisted laparoscopic radical prostatectomy. METHODS: Fifty patients scheduled for robot-assisted laparoscopic radical prostatectomy were divided into a zero-PEEP (ZEEP) group and a 5 cmH2O of PEEP (PEEP) group. Intraocular pressure, optic nerve sheath diameter, and respiratory and hemodynamic parameters were measured before induction (T0), 10 minutes after induction of general anesthesia in the supine position before CO2 insufflation (T1), 5 minutes (T2), and 30 minutes (T3) after steep Trendelenburg positioning with pneumoperitoneum, after desufflation of pneumoperitoneum in the supine position (T4), and after 30 minutes in the recovery room postoperatively (T5). RESULTS: There was no significant difference in intraocular pressure or optic nerve sheath diameter between the groups during the study. The partial pressure of arterial oxygen and dynamic lung compliance at T1, T2, T3, and T4 were significantly higher in the PEEP than in the ZEEP group. There was no difference in mean arterial pressure or heart rate between groups at any time. CONCLUSION: Applying 5 cmH2O of PEEP did not increase intraocular pressure or optic nerve sheath diameter during pneumoperitoneum with steep Trendelenburg positioning in robot-assisted laparoscopic radical prostatectomy. These results suggest that low PEEP can be safely applied during surgery with pneumoperitoneum and steep Trendelenburg positioning in patients without preexisting eye disease and brain pathology.

Measurements and Clinical Application of Anatomical Space for Transfrontal Pituitary Surgery Through Magnetic Resonance Imaging Reconstruction.

OBJECTIVE: This study aims to clarify the relative position of the normal important structures and anatomical spaces formed by the structures passed through during the transfrontal pituitary surgery, and discuss how to avoid some eloquent structures. METHODS: A total of 120 cases of magnetic resonance imaging images from normal adult brains were selected as the object of study and divided into male and female groups. The important adjacent structures of the pituitary passed through during the transfrontal pituitary surgery were marked on the reconstructed images. In all planes of the spaces passing through successively during the pituitary surgery, the morphological parameters such as the size, boundary, structure, and spatial extent of the spaces were measured. RESULTS: The size, boundary, structure, and spatial extent of the space between the 2 optic nerves, the space between the optic nerves and the pituitary stalk, and the space between the tuber cinereum and the interal carotid artery in the plane of the pituitary stalk were measured, the anterior part and the posterior part in male were shorter than those in female (P = 0.021; P = 0.029); no statistically significant difference was found in the measurements of the lengths and angles of these spaces. CONCLUSIONS: The authors' findings provide the surgeons with the detailed anatomical data and help to provide a morphological basis for intraoperative protection of the pituitary and vital adjacent structures and surgical approach.

Interdural course of the ophthalmic artery in the optic canal.

OBJECTIVE: In the current neurosurgical and anatomical literature, the intracanalicular segment of the ophthalmic artery (OphA) is usually described to be within the optic nerve dural sheath (ONDS), implying direct contact between the nerve and the artery inside the optic canal. In the present study, the authors sought to clarify the exact relationship between the OphA and ONDS. METHODS: Ten cadaveric heads were subjected to endoscopic endonasal and transcranial exposures of the OphA in the optic canal (5 for each approach). The relationship between the OphA and ONDS was assessed. Histological examination of one specimen of the optic nerve and the accompanying OphA was also performed to confirm the relationship with the ONDS. RESULTS: In all specimens, the OphA coursed between the two layers of the dura (endosteal and meningeal) and was not in direct contact with the optic nerve, except for the first few millimeters of the proximal optic canal before it pierced the ONDS. Upon reaching the orbit, the two layers of the dura separated and allowed the OphA to literally float within the orbital fat. The meningeal dura continued as the ONDS, whereas the endosteal dura became the periorbita. CONCLUSIONS: This study clarifies the interdural course of the OphA within the optic canal. This anatomical nuance has important neurosurgical implications regarding safe exposure and manipulation of the OphA.

The Analysis of Computed Tomography of Paranasal Sinuses in Nasal Septal Deviation.

OBJECTIVES: Anatomic variations of paranasal sinuses are frequent among population that should be analyzed and interpreted accurately. The purpose of this study is to analyze anatomical variants and their relationships of paranasal sinuses in patients with nasal septal deviation undergoing septoplasty. METHODS: A total number of 150 patients (74 males, 76 females) with nasal septal deviation undergoing septal surgery were included in this retrospective study. The authors analyzed the direction and the angle of the nasal septal deviation, variations of the nasal turbinates, ethmoidal air cells, paranasal sinus pneumatization, accessory pneumatization of the paranasal complex and sphenoid sinus-related structures and the Keros, optic nerve and Vidian canal classification, and relationships between these structures in the paranasal computed tomography of the patients. RESULTS: The incidence of concha bullosa, Onodi cell, and anterior clinoid pneumatization were higher in patients with nasal septal deviation when compared with current literature. CONCLUSION: Physicians and surgeons dealing with the nose and maxillofacial region should be able to analyze paranasal computed tomography by themselves and must be aware of these variations during performing septal and craniomaxillofacial surgery.

Effects of tourniquet usage in lower extremity surgery on optic nerve sheath diameter

Background/aim: The aim of this study was to evaluate changes in intracranial pressure following tourniquet deflation using noninvasive ultrasonographic optic nerve sheath diameter (ONSD) measurements. Materials and methods: Our study included 59 adult patients between the ages of 18 and 65 years from the American Society of Anesthesiologists (ASA) I/II risk groups who were scheduled to undergo elective orthopedic surgery of the lower extremities using a tourniquet under general anesthesia. ONSD and end-tidal CO2 (ETCO2) were measured 5 times: 15 min prior to the anesthesia induction; just prior to the deflation of the tourniquet; and at 5, 10, and 15 min after the deflation. Additionally, age, sex, weight, height, ASA score, and duration of operation and tourniquet usage were recorded. Results: The ONSD value measured 5 min after the deflation was significantly higher than all of the remaining measurements. There was a significant correlation between the ONSD and ETCO2 measurements at 5 and 10 min after deflation (r = 0.61, 95% CI 0.42-0.75, P < 0.0001 and r = 0.30, 95% CI 0.04-0.51, P < 0.05, respectively). Conclusion: The ultrasonographic ONSD measurements, which were obtained using a simple and noninvasive approach, increased significantly following tourniquet deflation, and this increase was correlated with an increase in ETCO2.

Real time optic nerve sheath diameter measurement during lumbar puncture.

Measurement of optic nerve sheath diameter (ONSD) using point of care ultrasound has been used to indirectly assess the intracranial pressure (ICP) particularly in conditions where it is raised. Direct pressure measurements using probes reaching the ventricle system correlated with ONSD using ultrasound. Attempts were made to measure the ONSD pre and post lumbar puncture (LP) after draining cerebrospinal fluid (CSF) as well as post ventricular shunt placement. We report ONSD measurement and demonstrate dynamic changes during LP in a patient with known idiopathic intracranial hypertension (IIH).