Eur Arch Otorhinolaryngol (2014) 271:3101–3105 DOI 10.1007/s00405-014-3149-5
CASE REPORT
A minimally invasive endoscopic transnasal approach to the craniovertebral junction in the paediatric population Sien Hui Tan · Dharmendra Ganesan · Narayanan Prepageran · Vicknes Waran
Received: 9 May 2014 / Accepted: 10 June 2014 / Published online: 2 July 2014 © Springer-Verlag Berlin Heidelberg 2014
Introduction
Case 1
Access to the craniovertebral junction can be extremely challenging owing to the complex anatomy of this area. The traditional transoral approach is widely recognized as the standard procedure, but is not without its limitations and drawbacks. The endoscopic transnasal route, first introduced by Kassam et al. [1], is minimally invasive and should be considered as a feasible alternative, particularly for the paediatric population. Few authors have described a purely endoscopic transnasal technique and their experiences mainly limited to one or two paediatric patients aged 10–15 [2–6]. To the best of our knowledge, we present the first paediatric case series consisting of the youngest reported patient as well as the first report on utilization of the endoscopic transnasal approach for biopsy and partial resection of a posterior fossa tumour.
A 13-year-old male with Type 1 Chiari malformation presented with progressive limb weakness for 2 months. He had a high stepping, unsteady gait with grade 4/5 motor strength in all extremities and increased reflexes. Computed tomography (CT) and magnetic resonance imaging (MRI) demonstrated Arnold–Chiari malformation type I with basilar invagination, worsening syringomyelia and tonsillar herniation (Fig. 1a). There was no evidence of hydrocephalus. He underwent an occipitocervical instrumentation and fusion followed by endoscopic transnasal odontoidectomy in the same operative setting.
Case reports We utilized an endoscopic transnasal approach in three patients. Main clinical features are reported in Table 1.
Case 2 A 12-year-old male presented with a 2-year history of progressive lower limb weakness, frequent falls and neck pain. Physical examination revealed grade 1/5 motor strength in all extremities and brisk reflexes. His CT and MRI showed atlantoaxial subluxation with basilar invagination and significant cord compression (Fig. 1b). He initially underwent a foramen magnum decompression with C1 laminectomy and occipitocranial fusion followed by endoscopic transnasal odontoidectomy 2 months later. Case 3
S. H. Tan (*) · N. Prepageran Department of Otolaryngology, Faculty of Medicine, University Malaya, Lembah Pantai, 50603 Kuala Lumpur, Malaysia e-mail: [email protected] D. Ganesan · V. Waran Department of Neurosurgery, Faculty of Medicine, University Malaya, Lembah Pantai, 50603 Kuala Lumpur, Malaysia
A 3-year-old male presented with a brief history of lower limb weakness. He had grade 2/5 motor strength in all extremities and brisk reflexes. MRI demonstrated a posterior fossa mass with spinal cord compression (Fig. 1c). He underwent a transnasal endoscopic biopsy and partial resection of the tumour and histology confirmed a rhabdomyosarcoma.
13
Transnasal endoscopic partial resection of the tumour Lower limb weakness Grade 2/5 motor strength Brisk reflexes
Sex
M
M
M
13
12
3
Posterior fossa rhabdomyosarcoma
Foramen magnum decompression with C1 laminectomy and occipitocranial fusion + endoscopic transnasal odontoidectomy (2-stage procedure)
Limb weakness High stepping, unsteady gait Grade 4/5 motor strength Increased reflexes Lower limb weakness Neck pain Grade 1/5 motor strength Brisk reflexes Type 1 Chiari malformation with basilar invagination
Surgical techniques
Age (year)
Atlantoaxial subluxation with basilar invagination and significant cord compression
Presentation Diagnosis
Occipitocervical instrumentation and fusion + endoscopic transnasal odontoidectomy (single-stage procedure)
Eur Arch Otorhinolaryngol (2014) 271:3101–3105
The patients were positioned supine with the head placed on a horse-shoe head rest. They were registered to the Medtronic AxiEM™ electromagnetic navigation system. Rigid-rod endoscopes 4 mm in diameter and 18 cm in length with lens angles of 0° and 30° were used and mounted on a digital video camera system (Karl Storz). In all patients, a two-nostril approach was utilised. A unilateral inferior turbinectomy was performed, followed by a septal flap and a posterior septectomy (Fig. 2a). The remaining contralateral inferior turbinate and bilateral middle turbinates were preserved. Both sphenoid ostea were marginally enlarged and the sphenoid keel removed (Fig. 2b). Our approach was a midline incision of the nasopharynx similar to Wu et al. [7], with a horizontal incision at the superior end giving a “T” shaped incision appearance. This incision was performed with a monopolar cautery from the lower third of the clivus to C2. The prevertebral muscles were dissected out with neuronavigation guidance to ensure adequate exposure of the lateral extent of the peg. Visual and neuronavigation confirmation were used to establish exposure of the clivus, C1 and C2 and extent of removal of the clivus and the arch of C1 (Fig. 2c, d). The odontoid peg was cored out with the high-speed drill and the shell removed using up-cut bone rongeurs and curettes. Finally, the ligaments posterior to the peg were removed. The adequacy of the decompression was confirmed with descent of the dura (Fig. 2e). The mucosa was approximated and a fibrin sealant (Tissel®) was used. Both nasal cavities were packed with Merocel® nasal tampons. In the final case, the dura was opened, and the lesion decompressed and biopsied. The dural defect was closed with a cartilage graft and a mucosal septal flap (Fig. 2f).
Results Patients 1 and 3 were extubated following surgery, but patient 2 required long-term tracheostomy care. All patients were allowed orally within a week and discharged well. There were no complications of cerebrospinal fluid (CSF) leakage or meningitis. Postoperative CT for cases 1 and 2 showed satisfactory resection of the odontoid (Fig. 3). Patient 3 underwent further debulking via a retrosigmoid approach. During follow-up, all patients remained neurologically intact with improvement in motor strength and balance.
13
3
2
1
Discussion No.
Table 1 Patient characteristics
Procedure(s)
3102
In paediatric patients, transoral access to the craniovertebral junction is an arduous task. The transnasal route is an
Eur Arch Otorhinolaryngol (2014) 271:3101–3105
3103
Fig. 1 a, b Preoperative sagittal CT scans demonstrating revealing basilar invagination with the tip of the odontoid peg projecting above the foramen magnum. c Preoperative MRI scan revealing a tumour at craniovertebral junction
Fig. 2 Intraoperative endoscopic images a View after the posterior part of the nasal septum and unilateral inferior turbinate are removed. The remaining contralateral inferior turbinate and both middle turbinates are preserved. b View after bilateral sphenoid ostea are widened and the sphenoid keel is removed. c The clivus, C1 and C2 are visual-
ized after the soft tissue has been reflected laterally. d The odontoid peg is exposed after removal of the anterior arch of C1. e Bulging of the dura is visualized ensuring adequate decompression. f Final view after repair with the mucosal septal flap
ideal alternative as it provides the most direct approach and offers excellent exposure superiorly. This approach is particularly beneficial in those with craniofacial abnormalities including micrognathia,
macroglossia or midface hypoplasia. The smaller mouth opening in children, which necessitates the use of mouth retractors, can dislocate the mandibular condyles, and cause tongue oedema and teeth damage [3, 5]. Moreover,
13
3104
Eur Arch Otorhinolaryngol (2014) 271:3101–3105
Fig. 3 a, b Postoperative sagittal CT scans revealing successful resection of the odontoid peg
adenoidal and tonsillar hypertrophy make it difficult to identify the midline [5]. In previous reported cases, the youngest patient was 10 years of age and we have successfully demonstrated the feasibilty of performing this procedure in a patient as young as 3 years old. One key limitation of the transoral route is the splitting of the soft and hard palate for sufficient rostral exposure [5]. Hence, prolonged palatal wound healing, hard palate fistula, swallowing difficulties and velopharyngeal insufficiency can occur [8]. The risk of infection is also lessened owing to minimal contamination of the wound with bacteria and saliva [1, 7]. However, when performing this procedure transnasally, a careful preoperative analysis of MRI images in the sagittal plane is required to ensure the entire pathology is above a plane that lies between the posterior aspect of the hard palate and the anterior aspect of the nasopharynx. There is reduced risk of upper airway oedema via the transnasal route, hence avoiding extended nasogastric tube feeding and prolonged intubation or tracheostomy [1, 3, 7]. Only one of our patients required a tracheostomy and this was performed preoperatively as he had previous prolonged ventilation leading to severe soft tissue swelling. No other patients had airway complications. Overall, recovery and hospitalization time are also shortened. We made several modifications to optimize access while minimizing invasiveness. By performing a unilateral inferior turbinectomy, we achieved sufficient space for instrumentation. Both middle turbinates were preserved to maintain normal laminar flow of air and decrease postoperative crusting [9]. Widening the sphenoid ostea inferiorly for better clivus exposure lessened the invasiveness but allowed identification of rostral key structures like carotid canals, medial pterygoid plates, pterygoid canal and vidian nerve. A midline incision reduced the risk of injury to the Eustachian tube and vidian nerve, and expedited wound healing. Nevertheless, there are concerns of a steeper learning curve requirement and a limited operative field in the
13
transnasal approach. The latter can cause restricted access below C2 and difficulty in repairing a dural tear, predisposing patients to persistent CSF leakage or meningitis [3, 4]. There was only one case of intraoperative CSF leak and upon repair, there were no further complications [2]. We did not encounter such problems in our cases. To our best knowledge, we describe the first case of a biopsy and partial resection of a posterior fossa tumour via an endoscopic transnasal method. Hence, our third case is extremely unique as the indications for operation in the previous papers were mainly for basilar invagination, atlantoaxial subluxation and retroflexed odontoid peg. While our case series is relatively small, it illustrates the usefulness of utilizing an endoscope to perform various procedures in the anterior craniovertebral junction and the possibility of reducing the morbidity associated with the transoral route in paediatric patients.
Conclusion We believe the endoscopic transnasal approach to the craniovertebral junction provides a potentially safer alternative in the paediatric population. Future studies should be conducted to analyse the validity of this novel technique. Acknowledgement One of the authors of this paper, Vicknes Waran, is supported by University of Malaya’s HIR-MOHE research grant initiative (H-50001-00-A000026). Conflict of interest None declared.
References 1. Kassam AB, Snyderman C, Gardner P, Carrau R, Spiro R (2005) The expanded endonasal approach: a fully endoscopic transnasal approach and resection of the odontoid process: technical case report. Neurosurgery 57:E213
Eur Arch Otorhinolaryngol (2014) 271:3101–3105 2. Magrini S, Pasquini E, Mazzatenta D, Mascari C, Galassi E, Frank G (2008) Endoscopic endonasal odontoidectomy in a patient affected by Down syndrome: technical case report. Neurosurgery 63:E373–E374 3. Hankinson TC, Grunstein E, Gardner P, Spinks TJ, Anderson RC (2010) Transnasal odontoid resection followed by posterior decompression and occipitocervical fusion in children with Chiari malformation Type I and ventral brainstem compression. J Neurosurg Pediatr 5:549–553 4. Patel AJ, Boatey J, Muns J, Bollo RJ, Whitehead WE, Giannoni CM, Jea A (2012) Endoscopic endonasal odontoidectomy in a child with chronic type 3 atlantoaxial rotatory fixation: case report and literature review. Childs Nerv Syst 28:1971–1975 5. Sinha S, Mirza S, Bishop N, Zaki H, McMullan J (2012) Endoscopic endonasal resection of the odontoid peg for paediatric basilar invagination. Br J Neurosurg 26:487–489
3105 6. Hickman ZL, McDowell MM, Barton SM, Sussman ES, Grunstein E, Anderson RC (2013) Transnasal endoscopic approach to the pediatric craniovertebral junction and rostral cervical spine: case series and literature review. Neurosurg Focus 35:E14 7. Wu JC, Huang WC, Cheng H, Liang ML, Ho CY, Wong TT, Shih YH, Yen YS (2008) Endoscopic transnasal transclival odontoidectomy: a new approach to decompression: technical case report. Neurosurgery 63:ONSE92–ONSE94 8. Tuite GF, Veres R, Crockard HA, Sell D (1996) Pediatric transoral surgery: indications, complications, and long-term outcome. J Neurosurg 84:573–583 9. Laufer I, Greenfield JP, Anand VK, Hartl R, Schwartz TH (2008) Endonasal endoscopic resection of the odontoid process in a nonachondroplastic dwarf with juvenile rheumatoid arthritis: feasibility of the approach and utility of the intraoperative Iso-C three-dimensional navigation. Case report. J Neurosurg Spine 8:376–380
13
CASE REPORT
A minimally invasive endoscopic transnasal approach to the craniovertebral junction in the paediatric population Sien Hui Tan · Dharmendra Ganesan · Narayanan Prepageran · Vicknes Waran
Received: 9 May 2014 / Accepted: 10 June 2014 / Published online: 2 July 2014 © Springer-Verlag Berlin Heidelberg 2014
Introduction
Case 1
Access to the craniovertebral junction can be extremely challenging owing to the complex anatomy of this area. The traditional transoral approach is widely recognized as the standard procedure, but is not without its limitations and drawbacks. The endoscopic transnasal route, first introduced by Kassam et al. [1], is minimally invasive and should be considered as a feasible alternative, particularly for the paediatric population. Few authors have described a purely endoscopic transnasal technique and their experiences mainly limited to one or two paediatric patients aged 10–15 [2–6]. To the best of our knowledge, we present the first paediatric case series consisting of the youngest reported patient as well as the first report on utilization of the endoscopic transnasal approach for biopsy and partial resection of a posterior fossa tumour.
A 13-year-old male with Type 1 Chiari malformation presented with progressive limb weakness for 2 months. He had a high stepping, unsteady gait with grade 4/5 motor strength in all extremities and increased reflexes. Computed tomography (CT) and magnetic resonance imaging (MRI) demonstrated Arnold–Chiari malformation type I with basilar invagination, worsening syringomyelia and tonsillar herniation (Fig. 1a). There was no evidence of hydrocephalus. He underwent an occipitocervical instrumentation and fusion followed by endoscopic transnasal odontoidectomy in the same operative setting.
Case reports We utilized an endoscopic transnasal approach in three patients. Main clinical features are reported in Table 1.
Case 2 A 12-year-old male presented with a 2-year history of progressive lower limb weakness, frequent falls and neck pain. Physical examination revealed grade 1/5 motor strength in all extremities and brisk reflexes. His CT and MRI showed atlantoaxial subluxation with basilar invagination and significant cord compression (Fig. 1b). He initially underwent a foramen magnum decompression with C1 laminectomy and occipitocranial fusion followed by endoscopic transnasal odontoidectomy 2 months later. Case 3
S. H. Tan (*) · N. Prepageran Department of Otolaryngology, Faculty of Medicine, University Malaya, Lembah Pantai, 50603 Kuala Lumpur, Malaysia e-mail: [email protected] D. Ganesan · V. Waran Department of Neurosurgery, Faculty of Medicine, University Malaya, Lembah Pantai, 50603 Kuala Lumpur, Malaysia
A 3-year-old male presented with a brief history of lower limb weakness. He had grade 2/5 motor strength in all extremities and brisk reflexes. MRI demonstrated a posterior fossa mass with spinal cord compression (Fig. 1c). He underwent a transnasal endoscopic biopsy and partial resection of the tumour and histology confirmed a rhabdomyosarcoma.
13
Transnasal endoscopic partial resection of the tumour Lower limb weakness Grade 2/5 motor strength Brisk reflexes
Sex
M
M
M
13
12
3
Posterior fossa rhabdomyosarcoma
Foramen magnum decompression with C1 laminectomy and occipitocranial fusion + endoscopic transnasal odontoidectomy (2-stage procedure)
Limb weakness High stepping, unsteady gait Grade 4/5 motor strength Increased reflexes Lower limb weakness Neck pain Grade 1/5 motor strength Brisk reflexes Type 1 Chiari malformation with basilar invagination
Surgical techniques
Age (year)
Atlantoaxial subluxation with basilar invagination and significant cord compression
Presentation Diagnosis
Occipitocervical instrumentation and fusion + endoscopic transnasal odontoidectomy (single-stage procedure)
Eur Arch Otorhinolaryngol (2014) 271:3101–3105
The patients were positioned supine with the head placed on a horse-shoe head rest. They were registered to the Medtronic AxiEM™ electromagnetic navigation system. Rigid-rod endoscopes 4 mm in diameter and 18 cm in length with lens angles of 0° and 30° were used and mounted on a digital video camera system (Karl Storz). In all patients, a two-nostril approach was utilised. A unilateral inferior turbinectomy was performed, followed by a septal flap and a posterior septectomy (Fig. 2a). The remaining contralateral inferior turbinate and bilateral middle turbinates were preserved. Both sphenoid ostea were marginally enlarged and the sphenoid keel removed (Fig. 2b). Our approach was a midline incision of the nasopharynx similar to Wu et al. [7], with a horizontal incision at the superior end giving a “T” shaped incision appearance. This incision was performed with a monopolar cautery from the lower third of the clivus to C2. The prevertebral muscles were dissected out with neuronavigation guidance to ensure adequate exposure of the lateral extent of the peg. Visual and neuronavigation confirmation were used to establish exposure of the clivus, C1 and C2 and extent of removal of the clivus and the arch of C1 (Fig. 2c, d). The odontoid peg was cored out with the high-speed drill and the shell removed using up-cut bone rongeurs and curettes. Finally, the ligaments posterior to the peg were removed. The adequacy of the decompression was confirmed with descent of the dura (Fig. 2e). The mucosa was approximated and a fibrin sealant (Tissel®) was used. Both nasal cavities were packed with Merocel® nasal tampons. In the final case, the dura was opened, and the lesion decompressed and biopsied. The dural defect was closed with a cartilage graft and a mucosal septal flap (Fig. 2f).
Results Patients 1 and 3 were extubated following surgery, but patient 2 required long-term tracheostomy care. All patients were allowed orally within a week and discharged well. There were no complications of cerebrospinal fluid (CSF) leakage or meningitis. Postoperative CT for cases 1 and 2 showed satisfactory resection of the odontoid (Fig. 3). Patient 3 underwent further debulking via a retrosigmoid approach. During follow-up, all patients remained neurologically intact with improvement in motor strength and balance.
13
3
2
1
Discussion No.
Table 1 Patient characteristics
Procedure(s)
3102
In paediatric patients, transoral access to the craniovertebral junction is an arduous task. The transnasal route is an
Eur Arch Otorhinolaryngol (2014) 271:3101–3105
3103
Fig. 1 a, b Preoperative sagittal CT scans demonstrating revealing basilar invagination with the tip of the odontoid peg projecting above the foramen magnum. c Preoperative MRI scan revealing a tumour at craniovertebral junction
Fig. 2 Intraoperative endoscopic images a View after the posterior part of the nasal septum and unilateral inferior turbinate are removed. The remaining contralateral inferior turbinate and both middle turbinates are preserved. b View after bilateral sphenoid ostea are widened and the sphenoid keel is removed. c The clivus, C1 and C2 are visual-
ized after the soft tissue has been reflected laterally. d The odontoid peg is exposed after removal of the anterior arch of C1. e Bulging of the dura is visualized ensuring adequate decompression. f Final view after repair with the mucosal septal flap
ideal alternative as it provides the most direct approach and offers excellent exposure superiorly. This approach is particularly beneficial in those with craniofacial abnormalities including micrognathia,
macroglossia or midface hypoplasia. The smaller mouth opening in children, which necessitates the use of mouth retractors, can dislocate the mandibular condyles, and cause tongue oedema and teeth damage [3, 5]. Moreover,
13
3104
Eur Arch Otorhinolaryngol (2014) 271:3101–3105
Fig. 3 a, b Postoperative sagittal CT scans revealing successful resection of the odontoid peg
adenoidal and tonsillar hypertrophy make it difficult to identify the midline [5]. In previous reported cases, the youngest patient was 10 years of age and we have successfully demonstrated the feasibilty of performing this procedure in a patient as young as 3 years old. One key limitation of the transoral route is the splitting of the soft and hard palate for sufficient rostral exposure [5]. Hence, prolonged palatal wound healing, hard palate fistula, swallowing difficulties and velopharyngeal insufficiency can occur [8]. The risk of infection is also lessened owing to minimal contamination of the wound with bacteria and saliva [1, 7]. However, when performing this procedure transnasally, a careful preoperative analysis of MRI images in the sagittal plane is required to ensure the entire pathology is above a plane that lies between the posterior aspect of the hard palate and the anterior aspect of the nasopharynx. There is reduced risk of upper airway oedema via the transnasal route, hence avoiding extended nasogastric tube feeding and prolonged intubation or tracheostomy [1, 3, 7]. Only one of our patients required a tracheostomy and this was performed preoperatively as he had previous prolonged ventilation leading to severe soft tissue swelling. No other patients had airway complications. Overall, recovery and hospitalization time are also shortened. We made several modifications to optimize access while minimizing invasiveness. By performing a unilateral inferior turbinectomy, we achieved sufficient space for instrumentation. Both middle turbinates were preserved to maintain normal laminar flow of air and decrease postoperative crusting [9]. Widening the sphenoid ostea inferiorly for better clivus exposure lessened the invasiveness but allowed identification of rostral key structures like carotid canals, medial pterygoid plates, pterygoid canal and vidian nerve. A midline incision reduced the risk of injury to the Eustachian tube and vidian nerve, and expedited wound healing. Nevertheless, there are concerns of a steeper learning curve requirement and a limited operative field in the
13
transnasal approach. The latter can cause restricted access below C2 and difficulty in repairing a dural tear, predisposing patients to persistent CSF leakage or meningitis [3, 4]. There was only one case of intraoperative CSF leak and upon repair, there were no further complications [2]. We did not encounter such problems in our cases. To our best knowledge, we describe the first case of a biopsy and partial resection of a posterior fossa tumour via an endoscopic transnasal method. Hence, our third case is extremely unique as the indications for operation in the previous papers were mainly for basilar invagination, atlantoaxial subluxation and retroflexed odontoid peg. While our case series is relatively small, it illustrates the usefulness of utilizing an endoscope to perform various procedures in the anterior craniovertebral junction and the possibility of reducing the morbidity associated with the transoral route in paediatric patients.
Conclusion We believe the endoscopic transnasal approach to the craniovertebral junction provides a potentially safer alternative in the paediatric population. Future studies should be conducted to analyse the validity of this novel technique. Acknowledgement One of the authors of this paper, Vicknes Waran, is supported by University of Malaya’s HIR-MOHE research grant initiative (H-50001-00-A000026). Conflict of interest None declared.
References 1. Kassam AB, Snyderman C, Gardner P, Carrau R, Spiro R (2005) The expanded endonasal approach: a fully endoscopic transnasal approach and resection of the odontoid process: technical case report. Neurosurgery 57:E213
Eur Arch Otorhinolaryngol (2014) 271:3101–3105 2. Magrini S, Pasquini E, Mazzatenta D, Mascari C, Galassi E, Frank G (2008) Endoscopic endonasal odontoidectomy in a patient affected by Down syndrome: technical case report. Neurosurgery 63:E373–E374 3. Hankinson TC, Grunstein E, Gardner P, Spinks TJ, Anderson RC (2010) Transnasal odontoid resection followed by posterior decompression and occipitocervical fusion in children with Chiari malformation Type I and ventral brainstem compression. J Neurosurg Pediatr 5:549–553 4. Patel AJ, Boatey J, Muns J, Bollo RJ, Whitehead WE, Giannoni CM, Jea A (2012) Endoscopic endonasal odontoidectomy in a child with chronic type 3 atlantoaxial rotatory fixation: case report and literature review. Childs Nerv Syst 28:1971–1975 5. Sinha S, Mirza S, Bishop N, Zaki H, McMullan J (2012) Endoscopic endonasal resection of the odontoid peg for paediatric basilar invagination. Br J Neurosurg 26:487–489
3105 6. Hickman ZL, McDowell MM, Barton SM, Sussman ES, Grunstein E, Anderson RC (2013) Transnasal endoscopic approach to the pediatric craniovertebral junction and rostral cervical spine: case series and literature review. Neurosurg Focus 35:E14 7. Wu JC, Huang WC, Cheng H, Liang ML, Ho CY, Wong TT, Shih YH, Yen YS (2008) Endoscopic transnasal transclival odontoidectomy: a new approach to decompression: technical case report. Neurosurgery 63:ONSE92–ONSE94 8. Tuite GF, Veres R, Crockard HA, Sell D (1996) Pediatric transoral surgery: indications, complications, and long-term outcome. J Neurosurg 84:573–583 9. Laufer I, Greenfield JP, Anand VK, Hartl R, Schwartz TH (2008) Endonasal endoscopic resection of the odontoid process in a nonachondroplastic dwarf with juvenile rheumatoid arthritis: feasibility of the approach and utility of the intraoperative Iso-C three-dimensional navigation. Case report. J Neurosurg Spine 8:376–380
13
