Cranial and Spinal Cerebrospinal Fluid Leaks: Foundations of Identification and Management.

Cerebrospinal fluid (CSF) leaks may occur at the skull base or along the spinal column and can cause a variety of debilitating neurological symptoms for patients. Recognizing the potential presence of a CSF leak and then identifying its source are necessary for accurate diagnosis and definitive treatment. A standardized workflow can be followed for successful leak localization, which often requires several diagnostic studies, and for definitive leak treatment, which can range from minimally invasive, needle-based approaches to a variety of surgical corrections. This review paper provides an overview of epidemiology, pathophysiology, and diagnostic workup for CSF leaks and introduces available treatment options. An illustrative case of a skull base CSF leak demonstrating diagnosis and surgical correction is provided.

Endoscopic Anatomy of the Skull Base.

Presently, endoscopic skull base surgery has undergone significant advancements since its inception over two decades ago. Nevertheless, it is imperative to underscore that the fundamental basis of all surgical procedures lies in the meticulous understanding of anatomy, with particular emphasis on the ventral anatomy. This facet has recently garnered increased attention.Following the advancements in endoscopic skull base surgery techniques, this chapter will concentrate on the pertinent anatomical considerations that serve as key foundations for successful procedures. These considerations are categorized into two planes: the sagittal plane and the coronal plane.The sagittal plane is further subdivided into five distinct approaches, namely,(1) the transcribriform approach, (2) the transplanum approach, (3) the transsellar approach, (4) the transclival approach, and (5) the transodontoid approach.On the other hand, the coronal plane is delineated into seven specific zones to facilitate comprehension and potential applications: (1) the petrous apex approach, (2) the intrapetrous approach, (3) the suprapetrous approach, (4) the cavernous sinus approach, (5) the infratemporal approach, (6) the medial condyle approach, and (7) the jugular foramen approach.By organizing the anatomical aspects in this systematic manner, the information provided becomes more accessible, fostering a comprehensive understanding of the subject matter for potential future application.

Transorbital Route to Intracranial Space.

The endoscopic superior eyelid transorbital approach has emerged as a notable and increasingly utilized surgical technique in recent years. This chapter presents an overview of the approach, tracing its historical development and highlighting its growing acceptance within the skull base community.Beginning with an introduction and historical perspective, the chapter outlines the evolution of the transorbital approach, shedding light on its origins and the factors driving its adoption. Subsequently, a comprehensive exploration of the anatomic bone pillars and intracranial spaces accessible via this approach is provided. Hence, five bone pillars of the transorbital approach were identified, namely the lesser sphenoid wing, the anterior clinoid, the sagittal crest, the middle cranial fossa, and the petrous apex. A detailed correlation of those bone targets with respective intracranial areas has been reported.Furthermore, the chapter delves into the practical application of the technique through a case example, offering insights into its clinical utility, indications, and limitations.

Design and Development of a Cost-Effective Transnasal Skull Base Bone Wax Applicator: A Technical Note.

Bone wax is an important hemostatic agent used in neurosurgical practice from more than a century. It acts by mechanical tamponade effect to stop the oozing from cancellous bone. Bone wax application over the skull surface over the vertex is easy and can be applied with fingers. In deeper areas, one uses dissector to apply the bone wax; however, it becomes difficult at times to apply in transnasal surgery using the same dissectors. Author designed a cost-effective 20-cm-long different angled bone wax applicator for skull base transnasal surgery. This applicator is cost-effective and not described previously in English literature.

[Meningiomas in the Central Skull Base:From the Perspective of Endoscopic Transnasal Surgery].

Recent advancements in endoscopic transnasal surgery(ETS)have expanded the application of this technique to meningiomas in the central skull base area, offering a less invasive alternative with a potentially lower physical burden on patients than conventional microscopic skull base surgery. Notably, while ETS allows surgeons to reach tumors without traversing the brain and nerves, thus theoretically reducing the risk of cranial nerve damage, it requires a high level of proficiency to avoid inadequate resection and tumor recurrence. In this article, we discuss the various surgical considerations, including preoperative imaging, surgical setting, nasal cavity expansion, skull base opening, tumor removal, and skull base reconstruction, as general procedures for specific meningiomas. We further describe the concept and details of our multi-layer fascial closure technique for dural repair in ETS, underlining the importance of skilled dural reconstruction in preventing postoperative complications. In conclusion, while ETS for skull base meningiomas presents a promising and less invasive treatment option, its success relies heavily on the surgeon's experience and understanding of the skull base anatomy, stressing the need for careful approach selection.

The effect of SARS-CoV-2 on the incidence of post-operative venous sinus thrombosis following skull base procedures.

PURPOSE: Sinus thrombosis is a common post-operative finding after posterior fossa surgery performed in the vicinity of the dural venous sinuses. The SARS-CoV-2 virus has been shown to confer an increased risk of venous thromboembolic events owing to eliciting a hyper-inflammatory and pro-thrombotic state. In this study, we examine the incidence of post-operative venous sinus thrombosis in patients undergoing peri-sigmoid posterior fossa surgery in the pre- and post-COVID era and investigate whether COVID infection confers an increased risk of sinus thrombosis. METHODS: A retrospective review of a single institution case series of patients underwent peri-sigmoid surgery (retrosigmoid, translabyrinthine, or far lateral) approach. Relevant clinical variables were investigated that may confer an increased risk of sinus thrombosis. RESULTS: A total of 311 patients (178 in the pre-COVID era, and 133 operated on after the pandemic began in March 2020) are included in the study. The composite incidence of sinus thrombosis seen on post-operative imaging was 7.8%. The incidence of sinus thrombosis in the pre-COVID cohort was N = 12 patients (6.7%) versus N = 12 (9%) in the post-COVID cohort (p = 0.46). A history of COVID infection was not shown to confer an increased risk of post-operative sinus thrombosis (OR: 0.61; 95% CI: 0.08-4.79, p = 0.64). Only a small number of patients (N = 7, 2.3%) required either medical or surgical intervention for post-operative sinus thrombosis. CONCLUSION: The overall incidence of post-operative sinus thrombosis is similar in the pre- and post-COVID era. The findings of this study suggest that COVID infection is not associated with a higher risk of venous sinus thrombosis.

Exploring optimal microscopic keyhole access to the skull base: an anatomical evaluation of transciliary supraorbital and transpalpebral orbitofrontal craniotomy approaches.

PURPOSE: The past two decades have witnessed the rise of keyhole microscopic minimally invasive surgeries, including the transciliary supraorbital approach (TCA) and transpalpebral approach (TPA), commonly known as the transorbital approach. This study aims to elucidate the nuances, specific indications, and advantages of each approach. METHODS: A series of dissections were conducted on five formalin-fixed, alcohol-preserved cadaver heads. The TCA was performed on one side, and the TPA on the other. Virtual measurements of working angles for both approaches were recorded. Additionally, three clinical cases were presented to illustrate the practical application of the techniques. RESULTS: For TCA, the craniotomy dimensions were 1.7 cm x 2.5 cm (Cranial-Caudal (CC) x Lateral-Lateral (LL)), while for TPA, they measured 2.1 cm x 2.9 cm (CC x LL). The measurements of anterior clinoid processes (ACP) were obtained and compared between approaches. In the TCA, the mean ipsilateral ACP measurement was 62 mm (Range: 61 -63 mm), and the mean contralateral ACP measurement was 71.2 mm (Range: 70 -72 mm). In TPA, these measurements were 47.8 mm (Range: 47 -49 mm) and 62.8 mm (Range: 62 -64 mm), respectively. TCA exhibited an average cranial-caudal angle of 14.9°, while TPA demonstrated an average of 8.3°. CONCLUSION: The anterior cranial fossa was better exposed by a TCA, which also featured shorter operative times, enhanced midline visualization, and a quicker learning curve. Conversely, the middle fossa was better exposed by a TPA, making it an excellent option for middle fossa pathologies, including those in the anterior temporal lobe. After sphenoid bone wing drilling, the TPA offers superior visualization from the lateral to the medial aspect and enhances the CC angle. Additionally, the TPA reduces the risk of postoperative frontalis palsy based on anatomic landmarks. However, the TPA requires a greater cranial osteotomy, and due to unfamiliarity with eyelid anatomy, the learning curve for most neurosurgeons is lengthier for this procedure.

Skull Base Aspergillus Infection Mimicking Tumor Recurrence: A Nasopharyngeal Carcinoma Case Study.

ABSTRACT: We report a case of recurrent nasopharyngeal carcinoma postnasopharyngectomy, presenting with headaches. MRI revealed abnormal signals of the clivus with enhancement, and FDG PET/CT indicated intense uptake in the nasopharynx, clivus, and left neck lymph nodes. Bone SPECT/CT showed bony erosion and uptake in bilateral skull base areas. Biopsy confirmed aspergillosis. Despite the challenges in distinguishing tumor invasion from Aspergillus infection on MRI, bone SPECT/CT, and FDG PET/CT, the short postsurgery period and extensive uptake suggested skull base osteomyelitis.

Suprapterional keyhole approach for anteromedial skull base lesions: How I do it.

BACKGROUND: For a minimally invasive treatment approach to the anteromedial part of the anterior cranial fossa (ACF), a small incision and craniotomy of the posterolateral part of the ACF are preferable. METHOD: We described the concept and technique of suprapterional keyhole approach (SPKA), which uses an exoscope and endoscope to treat ACF lesions. CONCLUSION: The SPKA enables ACF observation from the lateral direction; the endoscope's extended viewing angles enable the observation of the anteromedial part of the ACF, including the bilateral olfactory groove. Facial skin and large scalp incisions are avoided, making this approach efficient for ACF lesions.

Safety and efficacy of hydroset cranioplasty as an adjunct to gasket-seal and nasoseptal flap closure of the skull base. A case-controlled study.

BACKGROUND: Cerebrospinal fluid leak after endoscopic skull base surgery remains a significant complication. Several investigators have suggested Hydroset cranioplasty to reduce leak rates. We investigated our early experience with Hydroset and compared the rate of nasal complications and CSF leak rates with case-controlled historic controls. METHODS: We queried a prospective database of patients undergoing first time endoscopic, endonasal resection of suprasellar meningiomas and craniopharyngiomas from 2015 to 2023. We compared cases closed with a gasket seal, Hydroset, and a nasoseptal flap with those closed with only a gasket seal and nasoseptal flap. Demographics, technical considerations and postoperative outcomes (SNOT-22) were compared. RESULTS: Seventy patients met inclusion criteria, twenty patients in the Hydroset group (meningioma n = 12; craniopharyngioma n = 8) and 50 control patients (meningioma n = 25; craniopharyngioma n = 25). CSF diversion was used in fewer Hydroset patients (75%, 15/20) compared with control group (94%, 47/50; p = 0.02). CSF leak was less frequent in the Hydroset than the control group (5% versus 12%, p = 0.38). One Hydroset patient required delayed nasal debridement. SNOT-22 responses demonstrated no significant difference in sinonasal complaints between groups (Hydroset average SNOT-22 score 22.45, control average SNOT-22 score 25.90; p = 0.58). CONCLUSIONS: We demonstrate that hydroxyapatite reconstruction leads to improved CSF leak control above that provided by the gasket-seal and nasoseptal flap, without significant associated morbidity as long as the cement is fully covered with vascularized tissue.

Clinical application of transcranial neuroendoscopy combined with supraorbital keyhole approach in minimally invasive surgery of the anterior skull base.

To explore the techniques, safety, and feasibility of minimally invasive neurosurgery through the supraorbital eyebrow arch keyhole approach by neuroendoscopy. Retrospective analysis of clinical data of patients with various cranial diseases treated by transcranial neuroendoscopic supraorbital eyebrow keyhole approach in our hospital from March 2021 to October 2023. A total of 39 complete cases were collected, including 21 cases of intracranial aneurysms, 9 cases of intracranial space occupying lesions, 5 cases of brain trauma, 3 cases of cerebrospinal fluid rhinorrhea, and 1 case of cerebral hemorrhage. All patients' surgeries were successful. The good prognosis rate of intracranial aneurysms was 17/21 (81%), and the symptom improvement rate of intracranial space occupying lesions was 8/9 (88.9%). Among them, the initial symptoms of one patient with no improvement were not related to space occupying, while the total effective rate of the other three types of patients was 9/9 (100%). The average length of the craniotomy bone window of the supraorbital eyebrow arch keyhole is 3.77 ± 0.31 cm, and the average width is 2.53 ± 0.23 cm. The average postoperative hospital stay was 14.77 ± 6.59 days. The average clearance rate of hematoma by neuroendoscopy is 95.00% ± 1.51%. Our results indicate that endoscopic surgery through the supraorbital eyebrow arch keyhole approach is safe and effective for the treatment of anterior skull base lesions and cerebral hemorrhage. However, this retrospective study is a single center, small sample study, and the good surgical results do not exclude the subjective screening of suitable patients by clinical surgeons, which may have some bias. Although the clinical characteristics such as indications and contraindications of this surgical method still require further prospective and multicenter clinical research validation, our study still provides a new approach and choice for minimally invasive surgical treatment of anterior skull base lesions.

Tension Pneumocephalus Secondary to Positive Pressure Ventilation Following Endoscopic Endonasal Skull Base Surgery: Three-Year Follow-Up After Implementation of an Institutional Protocol.

BACKGROUND: Tension pneumocephalus (PMC) is a rare and feared complication following the endonasal endoscopic approach (EEA) to skull base procedures. This is a neurosurgical emergency that requires urgent decompression to avoid catastrophic neurologic damage or death. An avoidable cause is the application of positive pressure ventilation (PPV) in EEA patients for postoperative hypoxia. Our institution implemented a hospital-wide protocol in response to this to identify and manage at-risk patients; this paper aims to identify if this protocol was effective in lowering the rates of tension PMC secondary to PPV. RESULTS: In the 3 years following the implementation of the protocol, 110 patients underwent EEAs, from which 1 case of tension PMC (found to be not secondary to PPV) was identified. This is compared with 2 cases of tension PMC secondary to PPV over the preceding 5 years, out of 406 EEA patients. This constitutes a quantifiable reduction in PPV-related tension PMC in both standard and extended approach EEAs, signifying the effective uptake of the protocol. CONCLUSIONS: We found no cases of tension PMC after PPV following EEA skull base surgery in our institution since the implementation of an institution-wide guideline. This underscores the utility of our simple and cost-effective preventative protocol in reducing the overall rates of tension PMC following the inadvertent postoperative application of PPV. Further research is needed to study the comparative risks and benefits of PPV in the post-EEA patient and thus inform future iterations of the protocol.

Osseous bridging of the condylar fossa: report of a rare anatomical variation at the outer skull base.

PURPOSE: The topic of osseous variations of the craniocervical junction is a complex morphological and embryological chapter of human anatomy, with a possible impact on neurogical and vascular functionality in this morphological variable region. MATERIAL & METHODS: An until now undescribed anatomical variation of the exoccipital part of the occipital bone has been observed after maceration at the outer skull base of a West-European 68-year-old male body donor. RESULTS: On both sites of the foramen magnum accessory osseous processes were observed that arise from the jugular process and point towards the lateral margin of the foramen magnum. On the left site this process forms a full arc that bridges the condylar fossa completely. CONCLUSION: The observed osseous bridge over the condylar fossa has not been reported on before and can be explained by the partial persistence of a primordial vertebra between atlas and occipital bone: the Proatlas. The resulting accessory structure may affect due to its topographic conditions the V3-Segment of the vertebral artery and its accompanying nerves, and thus, play a role in diagnosis and therapy of vascular and/or neurological symptoms of head and neck.

[Overview and prospects of endoscopic skull base surgery].

Endoscopic skull base surgery presents significant technical challenges and high surgical risks, requiring collaboration among multiple disciplines such as otolaryngology, neurosurgery, ophthalmology, and oral maxillofacial surgery. In recent years, there has been rapid development in endoscopic skull base surgery, characterized by flourishing anatomical research and an expanding range of surgical indications. The future brings both opportunities and challenges, and endoscopic skull base surgery must grasp new directions in medical development, actively providing patients with safer and more effective treatment options.

[Clinical classification, staging and treatment strategy of radionecrosis of the nasopharynx and skull base].

Objective:To establish a staging system for guiding clinical treatment and prognostic risk assessment by retrospectively analyzing the cases with radionecrosis of the nasopharynx and skull base （RNSB） after radiotherapy for nasopharyngeal carcinoma. Methods:A total of 86 cases of RNSB from January 2019 to December 2022 visited Department of Otorhinolaryngology Head and Neck, the People's Hospital of Guangxi Zhuang Autonomous Region. Seventeen patients gave up the treatment, and 69 patients who underwent treatment were included for analysis. By analyzing the results of electronic nasopharyngolaryngoscopy combined with magnetic resonance （MR）, CT, and other imaging examinations, a staging system for RNSB was proposed. The relationship between the staging system and the surgical effectiveness and clinical prognosis was further analyzed. Results:According to the severity and extent of destruction of soft tissue, bone, and the adjacent neurovascular structures, the RNSB was categorized into closed type （n=5） and open type （n=64）, of which the open type was subdivided into five types: type Ⅰ（n=4）, type Ⅱ（n=6）, type Ⅲ（n=39, of which 21 cases were type Ⅲa and 18 cases were type Ⅲb）, type Ⅳ（n=12）, and type Ⅴ（n=8）. The clinical stage of RNSB were classified based on nasopharyngolaryngoscopy and imaging examinations, receiving the second course of radiotherapy or not, the involvement of the infection site, the extent of bone destruction, the degree of internal carotid artery involvement, and the degree of brain tissue necrosis: stageⅠ（1-2 scores）, 11 cases at stageⅡ（3-4 scores）, 24 cases at stage Ⅲ（5-6 scores）, and 30 cases at stage Ⅳ（ ≥ 7 scores or more）. Twenty-two patients chose conservative treatment （2 patients at stage Ⅰ, 3 patients at stage Ⅱ, 7 patients at stage Ⅲ, and 10 patients at stage Ⅳ）. Forty-seven patients chose nasal endoscopic surgical treatment （2 patients at stage Ⅰ, 8 patients at stage Ⅱ, 17 patients at stage Ⅲ, and 20 patients at stage Ⅳ）, of which 16 cases had received free mucosal flap and/or stented septum mucosal flap repair. Patients at stages Ⅰ, Ⅱ, and Ⅲ achieved satisfactory efficacy after surgical treatment. In addition, higher clinical stage was found to correlate with the worse prognosis and higher incidence of perioperative complications, which included failure of healing because of surgical site infection, cerebrospinal fluid nasal leakage, progressive osteonecrosis, nasopharyngeal hemorrhage, and death. Conclusion:The staging system proposed in our study can be used for early detection of RNSB during regular follow-up, and is also valuable for clinical treatment guidance and prognosis assessment.

[An anatomical road map of the parapharyngeal internal carotid artery in lateral and endoscopic ventral approaches].

Objective:To describe the road map of the lateral and endoscopic ventral approaches for the pharyngeal segment of the internal carotid artery, propose a sub-segmentation scheme, systematically and comprehensively understand its anatomical details and relationships with the surrounding structures. Methods:Five fresh cadaveric head specimens（10 sides in total） were dissected through lateral and endoscopic ventral approaches to evaluate the anatomical details of the parapharyngeal internal carotid artery and its relationship with the surrounding structures. Results:From the bifurcation of the common carotid artery to the vertical part of the internal carotid artery, alongside the direction of blood flow, the parapharyngeal internal carotid artery passes through four distinct anatomical tissues. Based on this, the parapharyngeal internal carotid artery can be divided into four sub-segments: nerve, muscle, fascia and osseous sub-segments. The boundaries and important adjacent structures of each segment are described in detail. Conclusion:The anatomical road map of the parapharyngeal internal carotid artery and the sub-segmentation scheme serving as a practical guide to navigate modular endoscopic skull base surgery of the parapharyngeal space while reduce the risk of internal carotid artery injury.

[Clinical analysis of 12 cases of solitary fibrous tumors in nasal cavity, sinuses and skull base].

Objective:To summarize and analyze the clinical manifestations, diagnosis and management and prognostic features of solitary fibrous tumor（SFT） in nasal cavity, sinus and skull base. Methods:The clinical data of 12 patients with STF from nasal cavity, sinus and cranial base admitted to the Affiliated Hospital of Qingdao University from April 2014 to January 2022 were retrospectively analyzed, including 4 patients admitted to the department of Otolaryngology head and neck surgery and 8 patients admitted to the department of skull base surgery The clinical characteristics, diagnosis, management and prognosis were analyzed. Results:Twelve patients were included in this research, including 7 males and 5 females. All patients received surgical treatment, and 4 patients also received postoperative adjuvant chemoradiotherapy. After follow-up for 12-60 months, 4 patients with adjuvant radiotherapy and chemotherapy had a good prognosis, and among 8 patients who did not receive radiotherapy and chemotherapy, 6 patients had good prognosis and 2 patients showed relapse. Four patients with a history of recurrence of SFT after surgery were admitted to our hospital for surgical treatment, in which 1 patient had relapse after surgery, and none had metastasis. Nasal cavity and sinus to skull base SFT is rare. The most effective treatment for this disease is surgical resection, and postoperative adjuvant chemoradiation and long-term follow-up can achieve a better prognosis. En bloc resection is the key to treatment success.

[Clinical analysis of resection and dura skull base reconstruction of cranionasal communication tumor in 31 cases].

Objective:To explore the methods of resection, dura and skull base repair and reconstruction of cranionasal communication tumor. Methods:Data of 31 patients with cranionasal communication tumor who underwent dura and skull base reconstruction after tumor resection from 2018 to 2022 were collected. Follow-up lasted for 3 to 41 months. Results:A total of 31 patients were enrolled, including 20 males and 11 females. The ages ranged from 19 to 74 years, with a median age of 57 years old. There were 17 benign lesions（one case of hemangioma, one case of Rathke cyst, one case of squamous papilloma, one case of craniopharyngioma, two cases of meningocele, two cases of varus papilloma, two cases of meningioma of grade Ⅰ, three cases of schwannoma, four cases of pituitary tumor） and 14 malignant lesions（one case of osteosarcoma, one case of poorly differentiated carcinoma, two cases of varus papilloma malignancy, two cases of olfactory neuroblastoma, two cases of adenocarcinoma, two cases of adenoid cystic carcinoma, four cases of squamous cell carcinoma） . Sixteen cases underwent nasal endoscopy combined with craniofacial incision and 15 cases underwent nasal endoscopy surgery alone. Complete resection of the mass and dura and skull base reconstruction were performed in all 31 patients, and free graft repair was performed in 8 cases（fascia lata in 5 cases and nasal mucosa in 3 cases）. Twenty-three cases were repaired with pedicled flaps（septal mucosal flap alone in 11 cases, septal mucosal flap combined with free graft in 6 cases, and cap aponeurosis combined with free graft in 6 cases）. Eight out of 31 patients underwent skull base bone repair. Postoperative cerebral hemorrhage occurred in 1 case, cerebrospinal fluid leakage in 1 case, intracranial infection in 2 cases. All patients were successfully treated without severe sequelae. Cerebrospinal fluid leakage and intracranial infection occurred in one patient after radiotherapy, who recovered after conservative treatment. All 17 patients with benign lesions survived. Thirteen out of 14 patients with malignant lesions received radiotherapy after surgery, nine survived without recurrence, five cases recurred, of which 2 survived with tumor, one underwent reoperation and 2 died. Conclusion:Cranionasal communication tumors are high-risk diseases of anterior and middle skull base, and various surgical repair methods could be selected after complete resection of the tumor. Successful reconstruction and multidisciplinary cooperation are crucial for treatment outcome.

A Case of Olfactory Neuroblastoma Developing Bilateral Retropharyngeal Lymph Node Metastasis 14-years After Skull Base Surgery.

Olfactory neuroblastoma (ONB) is an uncommon malignant tumor and is usually treated by a multidisciplinary approach includes surgery, radiotherapy, and chemotherapy. A 62 years-old male had a tumor in the nasal cavity and diagnosed as ONB with Kadish A stage. Anterior skull base surgery was performed as radical treatment. Since the surgical margin was negative, no postoperative radiotherapy was administered. 14 years after the surgery, bilateral otitis media with effusion (OME) was occurred, we found the recurrence tumor at bilateral retropharyngeal lymph node (RPLN) which surrounded the internal carotid arteries. Since these were unresectable, we planned chemoradiotherapy which was 70Gy of intensity modulated radiotherapy combined with two courses of carboplatin and etoposide. The tumor volume was reduced and bilateral OME were improved. He has been alive for 3 years after salvage treatment. Although ONB has a relatively good prognosis, it is known to often cause cervical lymph node metastasis. Grades III and IV of Hyams classification are considered high risk. This case, initial tumor was limited in the nasal cavity and its clinical classification was early stage, but Hyams classification was grade III. In reference to this case, considering that RPLN metastasis are difficult to radically resect at the salvage surgery, including this area in postoperative radiotherapy was considered an option.