Frontal Sinus Recess Research Articles

Light intensity distribution in images from rigid endoscopes used in minimal access sinus surgery.

Objectives/HypothesisTo investigate the pattern of intensity levels in images generated by the two most commonly used rigid endoscopes angulations in sinus surgery: 0° and 30°.MethodsAn enclosed light box containing an optical square grid, under endoscope illumination set just below saturation level, was used for measuring light distribution levels across test images. Endoscopes with 0° and 30° angulations were tested at 10 mm from the grid, typical for sinus surgery. The grid was set perpendicular to the axis of the shaft of the endoscope. The grayscale light intensity (GLI) levels (0 = black, 255 = white) in each of the grid squares were quantified from the digitized images.ResultsLight intensity was highly non‐uniform for both endoscopes. The brightest area of the field of view was at the center for the 0° endoscope and at about 20% of the image diameter proximally from the center for the 30° endoscope. For the 0° endoscope with a maximum value of about 230 GLI (90% of white saturation) at the center the minimum value was about 100 GLI at the periphery. The 30° endoscope with a similar maximum GLI value of 226 had a minimum of under 50 GLI at the most distant periphery, too dark for clear grid line definition.ConclusionThere are wide variations in light intensity across the image circle and much reduced illumination of the field edge. Surgeons should be aware of this fact so that accommodation can be made when surgical manipulation is performed away from the center of the endoscope field. This is especially relevant in angled cavities such as the frontal sinus recess, where the degree of angulation necessitates “edge of field” surgery.

High Variability of Postsurgical Anatomy Supports the Need for Individualized Drug-Eluting Implants to Treat Chronic Rhinosinusitis.

Chronic rhinosinusitis (CRS) is a common disease in the general population that is increasing in incidence and prevalence, severely affecting patients’ quality of life. Medical treatment for CRS includes self-management techniques, topical and oral medical treatments, and functional endoscopic sinus surgery (FESS). FESS is a standard procedure to restore sinus ventilation and drainage by physically enlarging the inflamed sinus passageways. Nasal drug-releasing stents are implanted to keep the surgically expanded aperture to the sinus frontalis open. The outcome of such an intervention is highly variable. We defined the anatomical structures which should be removed, along with ‘no-go areas’ which need to be preserved during FESS. Based on these definitions, we used cone beam computed tomography (CBCT) images to measure the dimensions of the frontal neo-ostium in 22 patients. We demonstrate anatomical variability in the volume and diameter of the frontal sinus recess after surgery. This variability could be the cause of therapy failure of drug-eluting implants after FESS in some patients. Implants individually made to fit a given patient’s postsurgical anatomy may improve the therapeutic outcome.

3D CT stereoscopic imaging: an improved anatomical understanding of the anterior ethmoid sinus and frontal sinus drainage pathway

OBJECTIVE: The objective of this presentation is to display a series of new anatomical concepts and terms regarding the frontal si- nus, its drainage pathway and cells vs. spaces of the anterior ethmoid, based on Three-Dimensional Computer X-ray Tomography Stereoscopic Imaging (3DCTSI) and contrast these concepts to those reported in the current literature. METHODS: Given the new anatomic observations provided by 3DCTSI, and the widespread anatomic variations a small sample was initially selected to describe our observations. Six exemplary cases according to the “Classification of Fronto-Ethmoidal cells” by Kuhn, Bent et al., Lee et al., expanded by Wormald et al., and adopted by Ramakrishnan et al., Huang et al., and Void et al. (1-7) were chosen to illustrate our detailed anatomic observations. Additional observations and data of prevalence identified in a larger series will follow. RESULTS and CONCLUSION: Conceptually, the anterior ethmoid “cells” are in essence “spaces” with openings that communicate with the middle meatus and/or the ethmoidal infundibulum. The frontal sinus and frontal recess are a united and continuous three-dimensional, irregularly shaped space, the Frontal Sinus/Recess Space (FSRS). The uncinate process has two segments: the Ethmoidal Uncinate Process (EUP), which encompasses the Infundibular Space of the EUP (IS-EUP), currently known as the Agger Nasi cell; and the Turbinal Uncinate Process (TUP), which borders the Turbinal Infundibulum (TI) medially. The superior attach- ment of the EUP will be detailed in each of the six cases (Table 2). The middle meatus and infundibular passages are the drainage pathways from the frontal sinus and maxillary sinus to the nasal cavity.

Evaluación radio-anatómica del receso del seno frontal en población colombiana

Objetivos: La cirugía endoscópica del seno frontal es quizá uno de los procedimientos más complejos en el manejo endoscópico de los senos paranasales debido a su localización anatómica y a las múltiples variantes anatómicas que pueden encontrarse durante su disección. Es indispensable conocer al detalle la anatomía de esta región en nuestra población para la planeación quirúrgica de los pacientes. Actualmente en nuestro país se desconoce la frecuencia de estas variaciones. El objetivo del proyecto es evaluar la frecuencia de las variables anatómicas del seno frontal y realizar un estudio radio-anatómico en una muestra de pacientes en Colombia.
 Diseño del estudio: Observacional, descriptivo de tipo transversal.
 Métodos: Muestra aleatorizada de 406 tomografías computarizadas de senos paranasales que incluyeron 812 senos frontales recolectados durante el año 2018
 Resultados: La celdilla suprabular fue la más comúnmente reportada con una frecuencia de 59.61%. La segunda celdilla fue la supra agger nasi con una frecuencia de 57.88%, seguido de la celdilla supra agger frontal (25.12%), celdilla suprabular frontal (22.17%), celdillas supraorbitarias (34.98%) y las celdilla frontal intersinusal (24,14%). La arteria etmoidal anterior se reportó colgante en un 31.28% y el diámetro AP más frecuente fue entre 5 -10 milímetros.
 Conclusiones: Para realizar una sinusotomía frontal endoscópica de forma adecuada es necesario conocer al detalle la anatomía del receso del seno frontal. Las diferentes variantes radio-anatómicas son muy frecuentes en el grupo poblacional estudiado. Creemos que este trabajo permitirá a los cirujanos un mejor entendimiento de esta región de difícil acceso quirúrgico en nuestra población.

Chronic rhinosinusitis and endoscopic sinus surgery.

Olfactory dysfunction is a major symptom reported by patients with chronic rhinosinusitis (CRS). Surgical treatment of this disease requires close surveillance of such dysfunction because of wide ranging implications for safety, quality of life, and impact on the flavor of foods and beverages. This review highlights key findings regarding the influences of endoscopic sinus surgery (ESS) on olfactory function across the unique presentations of CRS. Such findings provide information useful for informing patients of potential complications and for obtaining informed consent prior to surgical intervention. ESS has been shown to improve olfaction across all types of CRS as assessed through quantitative testing and subjective reports. The presence of nasal polyposis (NP) and eosinophilia have been identified as predictors of significant postoperative olfactory improvement. When indicated, judicious partial resection of the middle turbinate may result in improved olfactory function without a risk of long term complication. Careful attention to the olfactory cleft and frontal sinus recess are important in limiting olfactory complications by avoiding indiscriminate disruption of olfactory epithelium. Given the chronic nature of the disease, surveillance of olfactory function in patients with CRS is a lifelong activity that will evolve as emerging technologies become available.

Combined endonasal and eyelid approach for management of extensive frontal sinus inverting papilloma.

Sinonasal inverting papilloma (IP) is a benign but locally aggressive mucosal neoplasm with a high recurrence rate. Extension into the frontal sinus presents surgical challenges for endonasal resection. This study presents an orbitofrontal approach for managing extensive IP. Case series. Four patients seen between 2012 and 2016 with biopsy-proven IP with lateral frontal sinus extension underwent a combined endonasal and transpalpebral approach for tumor resection. Patient demographic data, preoperative characteristics, imaging, and follow-up data were compiled through retrospective chart review. Patients were selected for this approach when the tumor extended to the posterior frontal sinus wall, lateral frontal sinus recess, and orbit. Tumors were first approached endonasally until the frontal recess was reached. A Draf IIB or Draf III procedure was then performed to gain better exposure. Orbitofrontal exposure was achieved through an upper eyelid incision. Miniorbitofrontal craniotomy window was designed based on tumor location. Resection of the frontal and orbital extension was enhanced by endoscopic-assisted dissection through the orbitofrontal window. The transpalpebral approach provided access to all walls of the ipsilateral frontal sinus, the intersinus septum, and the medial aspect of the contralateral sinus. Complete tumor resection was achieved in all patients. There were no orbital complications, no visible eyelid asymmetry or scarring, and all patients had preserved forehead sensation. There were no recurrences on follow-up. Combining a transpalpebral orbitofrontal craniotomy with the endonasal approach allows complete resection of invasive IP with extension into the frontal sinus. This is achieved with great cosmetic results. 4. Laryngoscope, 128:3-9, 2018.

Correlation of frontal sinus recess anatomy with ethnicity, gender, and pathology

PurposeResearch on frontal sinus cells has been conflicting regarding relationship between frontal sinus cells and frontal sinus disease. There are no published studies regarding gender differences in frontal sinus disease. No comparisons between African Americans and Caucasians and frontal sinus disease have been published. This study attempts to define the above relationships as well as the relationship between number and types of cells and disease. MethodsA retrospective chart review was performed on sinus CT scans done from 2003 to 2011 at an academic medical center. Exclusion criteria included previous frontal sinus surgery, sinus malignancy, obvious trauma, congenital anomalies, and poor quality of scan. Number and type of frontal cells were recorded for 602 scans. Statistical analysis performed demographic comparisons and compared number and types of cells to evidence of disease. ResultsMales were more likely than females to have frontal sinus disease. Patients with Type 3 and Type 4 cells were more likely to have disease. No significant ethnic related differences in disease were found using a multivariate logistic regression model. Total number of cells did not significantly affect likelihood of disease. ConclusionsThis is one of the largest collections of data on frontal sinus cells as predictors of frontal sinus disease. These results suggest that gender and certain types of cells affect likelihood of disease. This study is the first to demonstrate a lack of difference in disease in African Americans and Caucasians. These results are significant regarding gender, race, number and type of cells as predictors of disease.

The Role of Balloon Sinuplasty in the Treatment of Vacuum Rhinogenic Headache.

In this study we tried to demonstrate how balloon sinuplasty could be an option in the treatment of the Rhinogenic Headache due to a probably disventilation of frontal sinus recess. 107 patients were included in the study with diagnosis of Rhinogenic Headache. The surgical group underwent bilateral balloon sinuplasty of the frontal sinus. The medical group underwent pharmacological treatment. Headaches characteristics were evaluated by a clinical personal diary. The severity was recorded by Visual Analog Scale 4 and 8months after treatment. 98 out of 107 patients completed the protocol. In surgical group and in medical one the mean headache score improved at four and eight months follow up. The headache frequency attacks per month decrease from a preoperative frequency of 18 (±4 SD) in surgical group and 17 (±3 SD) in medical group to 3 (±1 SD) and 6 (±3 SD) respectively at 4months control but increased slightly to 5 (±2 SD) and 12 (±4 SD) after 8months. We concluded that the balloon sinuplasty should be considered as an effective alternative option after an accurate selection of surgical candidates. However, it is important a 6-8month follow-up to evaluate the efficacy and stability of the treatment used.

A novel biodegradable frontal sinus stent (MgNd2): a long-term animal study.

The frontal sinus recess consists of anatomically narrow passages that are prone to stenosis in endonasal frontal sinus surgery for chronic sinus disease. Over the past 100years, diverse frontal sinus stents have been developed and evaluated in clinical and animal studies. However, superinfection, formation of granulations tissue, stent dislocation and late stenosis of the duct have remained challenges and subject of debate in the literature. Currently developed biodegradable materials, including rare earth-containing magnesium alloys are promising candidates for application as temporary implant materials. The Mg 2% wt Nd alloy (MgNd2) was used to design a nasal stent that fit the porcine anatomy. In the current study, we evaluate biocompatibility, biodegradation and functionality of a frontal sinus stent in 16 minipigs over 6months. Intraoperative endoscopy revealed free stent lumen in all cases. Blood examination and clinical examinations indicated no systematic or local inflammation signs. The histopathology and elements analysis showed a very good biocompatibility. The μ-computed tomography-based volumetric analysis showed substantial stent degradation within 6 months. Our MgNd2 based stent appears to be a promising, solid basis for the development of a frontal sinus stent for clinical use.

Modified subtotal‐Lothrop procedure for extended frontal sinus and anterior skull‐base access: a case series

The endoscopic modified Lothrop procedure (EMLP) is well established for resistant frontal sinus disease and anterior skull base (ASB) exposure. However, this technique may be unnecessarily aggressive by removing avoidable sinonasal structures in select cases. Previously, in a cadaveric study, we proposed a modification of the EMLP, termed the modified subtotal-Lothrop procedure (MSLP), to access the ASB and to address complex frontal sinus disease, for which access to the bilateral frontal sinus posterior table is required. This study provides a step-by-step description of this technique, and presents our experience in 5 patients who underwent this approach. A retrospective analysis was performed at a tertiary referral center on all patients undergoing endoscopic ASB resection and complex frontal sinus surgeries between May 2011 and May 2013. Of 8 patients identified who underwent an MSLP, 5 had at least 1-year follow-up. All patients underwent successful ASB exposure via the MSLP without complications and preservation of one frontal sinus recess. Adequate access to the bilateral posterior frontal sinus table was achieved in all cases. A patent frontal sinus drainage pathway could be assessed endoscopically after a mean follow-up of 18.6 (range, 12-27) months. The MSLP is a feasible approach for exposure of the ASB and accessing complex frontal sinus pathology. This modification provides adequate ASB exposure and surgical maneuverability similar to the EMLP, while preserving one frontal sinus recess. This modification was successful in providing adequate exposure and maneuverability as well as maintaining frontal sinus patency in this small cohort.

Endoscopic Frontal Sinus Surgery

Surgery on the frontal sinus or frontal recess remains a challenge for rhinologist because of its variability and complex anatomy. Its location, relatively complex and narrow frontal recess also make visualization difficult and predispose it to stenosis. Significantly, serious complications are possible due to the anterior ethmoidal artery, orbit and anterior cranial fossa. An understanding of frontal sinus and frontal recess anatomy is essential to perform endoscopic frontal sinus surgery. This paper examines frontal sinus anatomy and then variable procedures of endoscopic frontal sinus surgery. The selection of less invasive procedure as possible after assessment of the patient’s history, diagnostic endoscopy, and the CT scan makes successful endoscopic treatment of frontal sinus diseases. Korean J Otorhinolaryngol-Head Neck Surg 2014;57(10):657-63 Key WordsZZEndoscopic sinus surgery ㆍFrontal recess ㆍFrontal sinus.

Modified Subtotal Lothrop Procedure for Extended Frontal Sinus and Anterior Skull Base Access: A Cadaveric Feasibility Study with Clinical Correlates

Objective The endoscopic modified Lothrop procedure (EMLP) is an established approach for recalcitrant frontal sinus disease and anterior skull base exposure. However, in select cases, this technique may involve unnecessary resection of sinonasal structures. In this study, we propose a modification of the EMLP, termed the modified subtotal-Lothrop procedure (MSLP), to access the anterior skull base and complex frontal sinus disease for which access to the bilateral frontal sinus posterior table is required. Methods A cadaveric dissection with photo documentation was performed at an academic medical center on four cadaver heads using standard endoscopic techniques to demonstrate the MSLP and its feasibility. Results The endoscopic MSLP allowed ample access for instrumentation in each of the dissections using a 30- or 70-degree endoscope. Adequate bilateral access to the posterior table of the frontal sinus was gained in all cases without the need for dissection of the contralateral frontal sinus recess (FSR). Conclusion The MSLP appears to be a feasible technique for exposure of the anterior skull base and accessing complex frontal sinus pathology. This modification provides similar anterior skull base exposure and surgical maneuverability as the EMLP while limiting surgical dissection to one FSR, thereby preserving as much of the natural mucociliary drainage pathways as possible.

In-office Balloon Dilation and Drainage of Frontal Sinus Mucocele

Treatment of frontal sinus disease represents one of the most challenging aspects of endoscopic sinus surgery. Frontal sinus mucocele drainage may be an exception to the rule because in many instances, the expansion of the mucocele widens the frontal sinus recess and renders surgical drainage technically undemanding. Recently, there has been an increased interest in in-office procedures in otolaryngology because of patient satisfaction and substantial savings of time and cost for both patients and physicians. Similarly, the past few years have witnessed an increased use of balloon dilation devices in sinus surgery. Previously, we have described the in-office use of this device in treating patients who failed prior conventional frontal sinusotomy in the operating room. In this report, we describe our step-by-step in-office experience using this tool for drainage of a large frontal sinus mucocele.

High-resolution computed tomography analysis of the frontal sinus ostium: A pilot study

PurposeIdentification and exposure of the frontal sinus recess (FSR) during endoscopic sinus surgery (ESS) are challenging due to the variable anatomy, the narrow opening of the frontal sinus ostium (FSO), and the proximity of vital anatomic structures. Hence, a strong understanding of frontal sinus anatomy is required to prevent intracranial entry. Consistent and easily identifiable landmarks and measurements could assist safe entry into the FSO. In this study, we determine the distances from the columella and anterior nasal spine (ANS) to the nasofrontal beak (NFB) and anterior skull base (ASB) using high-resolution computed tomography (HRCT) scans. MethodsA radiographic analysis was performed at a tertiary care medical center. Measurements from the ANS to the NFB and ASB, and from the columella to the NFB and ASB were made using sagittal HRCT. Thirty-two HRCT scans were analyzed by three observers, and the mean distances and standard deviations were calculated. ResultsThe mean distance from the ANS to the NFB was 52.3±3.4mm in men and 47.7±3.5mm in women (p<0.0001). Mean distance from the ANS to the ASB was 61.8±4.1mm in men and 56.5±4.1mm in women (p<0.0001). Mean distance from the columella to the NFB was 58.9±2.3mm in men and 53.0±3.3mm in women (p<0.0001), and from the columella to the ASB was 67.9±3.7mm in men and 61.3±4.1mm in women (p<0.0001). ConclusionWhile performing FSR exposure in ESS, it is recommended to stay a distance of less than 66.9mm in men and 60.6mm in women from the columella to minimize intracranial complications.

Mapping the frontal sinus ostia using virtual endoscopy

To determine the relative location of the frontal sinus opening to other frontal cells using virtual endoscopy; and to assess whether the relative location of the frontal sinus ostium can be predicted. Retrospective analysis of high-resolution computed tomography scans from 50 adult patients without frontal sinus disease or previous sinus surgery. Using virtual endoscopy software, 100 frontal recesses were mapped for the presence and relative position of the frontal sinus ostium to the following cells: agger nasi (ANC); frontal bullar; frontal types 1, 2, and 3; supraorbital ethmoid; suprabullar; and intersinus septal cells. ANC and frontal type 3 cells were present in 92% and 45% of frontal recesses, respectively. All other cell types had a prevalence of ≤ 25%. Fifty percent of recesses had two rows of ostia anterior to posterior (AP), and the frontal opening was anterior in 52%. When there were three rows of cells AP (39%), the frontal opening was in the center in 64% of cases. Thirty-five percent of recesses had two rows of ostia medial to lateral (ML), and the frontal opening was medial 80% of the time. When there were three rows of openings ML (45%), the frontal opening was in the center 56% of the time. The frontal sinus recess is variable and complex. Virtual endoscopy can be used to analyze the frontal recess and assist in presurgical planning. Although there is variability in the ostial configuration present in the frontal recess, the probable position of the frontal sinus ostium can be predicted.

Modified mini‐lothrop/extended draf IIB procedure for contralateral frontal sinus disease: a case series

Management of frontal sinus disease represents one of the most challenging aspects of endoscopic sinus surgery. In select cases, anatomic variations (outflow tract osteoneogenesis, scarring, fat prolapsed from previous orbital decompression) may hinder ipsilateral access using traditional endoscopic approaches. We previously proposed a modification of the standard Draf IIB procedure which incorporates a frontal intersinus septectomy (modified mini-Lothrop procedure/extended Draf IIB) to access and manage recalcitrant unilateral frontal sinus obstruction inaccessible ipsilaterally in cadaver specimens. In this study, we describe this technique, and present a case series of 4 patients who benefited from this approach. A retrospective analysis at a large tertiary referral center was performed on all patients undergoing frontal sinus surgery between July 2008 and June 2011. Four patients with frontal sinus recess obstruction inaccessible from the ipsilateral side and treated with the modified mini-Lothrop procedure/extended Draf IIB were identified. All 4 patients underwent successful frontal sinusotomies via a Modified mini-Lothrop procedure/extended Draf IIB without complications and had a patent drainage pathway assessed endoscopically after a mean follow-up of 21 (range, 9-28) months. The modified mini-Lothrop procedure/extended Draf IIB represents a feasible approach and adequate alternative to more traditional endoscopic and open frontal sinus procedures in select cases. This modification was successful in addressing difficult to access unilateral frontal sinus disease in this small cohort.

Endoscopic endonasal surgery for recurrent cerebrospinal fluid rhinorrhea

Conclusions: CT and MRI are helpful to detect the precise site of the fistula, which is crucial for carrying out the repair, and transnasal endoscopic surgery is an effective treatment for recurrent cerebrospinal fluid (CSF) rhinorrhea. Objective: To discuss the cause and treatment of recurrent CSF rhinorrhea. Methods: A retrospective study was undertaken to analyze the clinical characteristics of 32 patients with recurrent CSF rhinorrhea. After detailed examination and radiological evaluation by CT and MRI, all of them underwent transnasal endoscopic surgery. Results: Six patients presented a leakage at the posterior wall of the frontal sinus, 12 at the ethmoid roof, and 14 at the sphenoid roof. Four cases with a defect in the frontal sinus and frontal recess were repaired with the DRAF III procedure, four cases with a defect in the sphenoid lateral recess were repaired through transpterygoid intervention and under an image-guided navigation system, while the others were operated by routine endoscopic sinus surgery. No recurrence was found during the follow-up for 14–60 months (mean 36.8) in 31 cases, and 1 case with recurrence recovered well after further surgery.

Three-dimensional reconstruction based on computed tomography images of the frontal sinus drainage pathway

This study aimed to investigate the utility of three-dimensional reconstructions of paranasal sinus computed tomography data in depicting the anatomy of the frontal sinus drainage pathway. Twenty-nine patients underwent imaging of the sinuses for various clinical indications. Variations in frontal sinus recess anatomy were determined from 0.75-mm thick coronal, axial and sagittal computed tomography images. Three-dimensional, reformatted images were generated from manually segmented volumes of interest. Observations were made on the variation and usefulness of these reconstructions. Three-dimensional, reformatted images of segmented volumes aided delineation of the spatial relationships of the frontal sinus, frontal sinus drainage pathway, infundibular and meatal direction of drainage, agger nasi cells, ethmoid bulla cells, supraorbital cells, and suprabullar cells. Three-dimensional, reformatted images of frontonasal anatomy enable improved understanding of the frontal sinus drainage pathway anatomy and of the spatial relationships between ethmoid air cells in this region. Such images may provide a useful adjunct to surgical planning and education.

Study of the cells of frontal recess region with multi-detector CT multiplanar reconstruction and clinicaI significance

Objective To observe the cells of frontal recess region with multi-detector CT muhiplanar reconstruction(MPR).Methods One hundred patients without the disease of frontal sinus and frontal recess region underwent axial multi-detector CT scan with axial,coronal and sagittal multiplanar reconstruction.Results In 100 cases(200 sides),the agger nasi cell is present in 186 sides(93.0%),the frontal cells were identified in 88 sides(44.0%),the prevalence of type Ⅰ,type Ⅱ,type Ⅲ and type Ⅳ cells were 51 sides(58.0%),23 sides(26.1%),14 sides(15.9%)and 0 sides,respectively. The suprabullar cells,the frontal bullar cells and the supraorbital ethmoid cells were identified in 130 sides (65.0%),23 sides(11.5%)and 11 sides(5.5%),respectively.The interfrontal septal cells were identified in 36 sides(18.0%).There was no significant difference between males and females,as well as between left and right side(P＞0.05).Conclusion With MPR imaging,doctors could better understand the frontal recess region,which is helpful to the endoscopic frontal sinus surgery. Key words: Frontal sinus; Tomography; X-ray computed

Endoscopic Surgery for Frontal and Ethmoid Sinus Mucoceles

Seven patients with frontal and ethmoid mucoceles treated by endoscopic sinus surgery were reviewed. Five cases were successfully managed, with two requiring a trephine procedure in combination with the intranasal endoscopic approach. Follow-up ranged from 3 to 33 months with a mean of 17.8 months. The use of endoscopic instruments through a trephine incision is recommended in difficult cases to assure patency of the frontal sinus recess. When a large frontal sinus mucocele extends into the anterior ethmoid, the endoscopic approach becomes ideal. Sinus mucoceles can be handled safely and successfully by endoscopic surgery and may eliminate the need for more traditional external procedures.