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Paper text:
stridor is a high - pitched sound caused by turbulent air flowing through a narrowed airway
. it can be inspiratory with obstruction at the supraglottic and glottis level , biphasic with obstruction at the subglottic level , and expiratory with obstruction in the trachea .
obstruction at the nasopharyngeal level often produces low - pitched inspiratory noise called stertor or snoring .
although the commonest cause is laryngomalacia , there are secondary airway lesions ( sals ) and other causes such as vocal cord palsy , subglottic stenosis , tracheal anomaly , laryngeal cleft , vascular and lymphatic malformation , laryngeal papillomas , craniofacial abnormalities , and even head and neck tumours [ 1 , 2 ] .
persistent stridor deserves careful assessment and proper investigation instead of just labeling it as a benign condition such as laryngomalacia .
  a proper history provides useful information on the differential diagnosis , severity , and level of obstruction .
questions should include the nature of the stridor , inspiratory , biphasic , or expiratory ; onset of stridor , aggravating factors , relationship with positioning , quality of cry , feeding difficulties , choking or aspiration , growth , perinatal history , and intubation history . for clinical assessment ,
the severity of respiratory distress should be first noted by examining the degree of insucking at the suprasternal and subcostal level , the degree of stridor , air entry , and relationship with positioning .
attention should also be paid to on any dysmorphic facial features , micrognathia , macroglossia , craniofacial abnormalities , voice quality , and cutaneous haemangiomas .
nasal patency can be checked by the cold - mirror test or passage of a suction catheter .
all patients referred to us with persistent stridor will be first examined awake with flexible laryngoscopy .
flexible laryngoscopy provides information on the dynamic function of the larynx . without the use of local anesthesia ,
the vocal cord mobility can be accurately assessed . besides , the degree of laryngomalacia , severity of retroglossal obstruction caused by micrognathia or macroglossia , intranasal masses , choanal atresia , and tongue base lesions can be evaluated .  
rigid laryngotracheobronchoscopy ( ltb ) under general anaesthesia is the second step in selected patients .
indications include patients with severe stridor , biphasic stridor , failed extubation , frequent aspiration and choking , desaturation during feeding , x - rays suggestive of subglottic or tracheal obstruction , atypical croup , and clinical suspicion with previous intubation . in our centre , rigid ltb is performed in the operation theatre by our special paediatric anaesthetist .
we adopt the tubeless technique with the infant maintained under general anaesthesia and spontaneous ventilation .
this allows a complete examination of the larynx in particular the subglottis and the trachea .
the subglottis can be sized with different sizes of endotracheal tubes in cases suspected to have subglottic stenosis .
, surgical intervention can be performed in the same setting after diagnosis by ltb such as supraglottoplasty with co2 laser for laryngomalacia , laser ablation for subglottic haemangiomas and laryngeal papillomas , laser resection and balloon dilatation for subglottic stenosis , and repair of cleft under microscope .
  infants with stridor undergoing rigid laryngotracheobronchoscopy ( ltb ) at queen mary hospital , university of hong kong between january 2005 and may 2011 were retrospectively evaluated .
secondary airway lesions ( sals ) occurred in 15 out of 57 patients with laryngomalacia ( table 2 ) .
  accurate diagnosis allows early intervention to relief upper airway obstruction and recovery of normal airway function .
majority of surgery could be safely performed in the early infantile period including laser surgery and repair , surgical resection of tumours , and reconstruction of the pharynx and skull base .
it usually presented as inspiratory stridor at the first few days or weeks of life .
although the majority of cases are self - limiting , severe stridor with respiratory distress , feeding difficulty , or failure to thrive deserves investigation and intervention .
flexible laryngoscopy demonstrates endoscopic features of laryngomalacia with tubular epiglottis , short aryepiglottic fold , and redundant arytenoids mucosa .
rigid laryngotracheobronchoscopy is useful to further rule out secondary airway lesions ( sals ) which occurred in 26% of laryngomalacia in our series .
the commonest sal in our series is subglottic stenosis followed by tracheomalacia which is compatible to the literature . as a tertiary referral centre
, most of the cases referred to us have severe laryngomalacia with feeding difficulty , choking , or failure to thrive requiring intervention .
laser aryepiglottoplasty with co2 laser can be safely performed under spontaneous ventilation and tubeless technique to resect the redundant arytenoids mucosa and to release the short aryepiglottic folds ( figure 1 and figure 2 ) .
postoperatively , our patient will be given steroid and monitored in intensive care unit for one day .
feeding can be resumed on the day of the surgery and patients can be discharged on the second day after operation .  
the majority are idiopathic while others are secondary to pathologies of the central nervous system such as arnold - chiari malformation , hydrocephalus , or cerebral palsy .
cases with respiratory distress require tracheostomy . spontaneous recovery may occur in some patients , while definitive surgery for decannulation such as vocal cord lateralization , cordectomy , or arytenoidectomy could be performed in adolescence period .
unilateral vocal cord palsies are usually iatrogenic cause after cardiac surgery or pda ligation . fortunately , most of them are well compensated and well tolerated . in our centre
, patients with glottic insufficiency or aspiration can undergo injection laryngoplasty with hyaluronic acid or fat to medialise the palsied vocal cord .  
it is defined as a diameter of less than 4  mm of the cricoid region in a full - term infant and less than 3  mm in a premature infant [ 1 , 2 ] .
accurate assessment and sizing of the subglottis can be performed during rigid laryngotracheobronchoscopy with different sizes of endotracheal tubes .
cotton - myer grade i and ii subglottic stenosis with excess fibrous connective tissue or granulations can be treated with multiple sessions of co2 laser under spontaneous ventilation and tubeless technique to avoid a tracheotomy .
severe subglottic stenosis will necessitate tracheostomy followed by laryngotracheal reconstruction ( ltr ) with rib cartilage to augment the subglottis .
an age - appropriate size endotracheal tube specially trimmed with the upper end sutured to prevent aspiration was placed as a laryngeal stent for 6 weeks until the rib graft was taken ( figure 3 ) .  
subglottic haemangioma is usually presented by 6 months of age as inspiratory or biphasic stridor .
unilateral subglottic haemangiomas can be successfully treated with co2 laser ablation and systemic steroid . in the past , the majority of circumferential haemangiomas required tracheostomy although open submucosal resection has been performed . in 2008 ,
a paper on the first successful use of oral propranolol for cutaneous haemangiomas in 11 children was published .
this was followed by 2 papers of propranolol therapy on subglottic haemangiomas [ 7 , 8 ] .
the mechanism of action is that propranolol induces apoptosis and decreases the production of endothelial vascular and fibroblastic growth factors ( vegfs and fgf ) .
one of our patients , a 6-month - old girl , presented with extensive haemangioma involving the subglottis , posterior pharyngeal wall , and cervical esophagus . tracheostomy was performed for the circumferential haemangioma . however , there was no sign of resolution or shrinkage of the haemangioma at the age of two .
diagnosis can be missed with flexible laryngoscopy as the larynx may appear as normal . in suspected cases ,
the extent can be nicely shown with a vocal cord spreader ( figure 4 ) .
however , if aspiration or pneumonia is frequent , repair can be performed endoscopically [ 10 , 11 ] . in our practice , we advocate the use of spontaneous ventilation and the tubeless anaesthetic technique .
a v - shaped incision was made around the cleft to create a raw surface .
the mucosa was then approximated with 5/0 vicryl , and an age - appropriate endotracheal tube was inserted as a laryngeal stent to allow healing of the wound .
the patient was then transferred to intensive care unit for 10 days and extubated when the wound was healed .  
congenital head and neck tumours can lead to stridor and upper airway obstruction in newborns .
differential diagnoses include teratomas , haemangiomas , lymphatic malformations , and neuroglial heterotopias [ 12 , 13 ] . nowadays
, these tumours can be detected early in the antenatal period by fetal ultrasound or mri .
well - planned delivery by exit ( ex - utero intrapartum treatment ) has been carried out in our patient with anticipated airway obstruction caused by a huge neuroglial heterotopias .
this is an extension of standard caesarean section with the baby partially delivered while the umbilical cord was kept intact to maintain maternal - fetal circulation to allow time for intubation and to secure the airway . in our centre
pharyngeal defects after resection in infants can be safely reconstructed with a locoregional flap created by the excessive skin , while the skull base defect can be reconstructed by spitting the cranial bone .
early resection and reconstruction can avoid prolonged intubation or tracheostomy and thus allow early recovery of normal airway function .
persistent symptoms deserve referral to otorhinolaryngologists for flexible and rigid endoscopy . surgical intervention from laser surgery to major resection and reconstruction
stridor is the main symptom of upper airway obstruction in infants . 
 it can be congenital or acquired , acute or chronic . 
 pathologies can be located from the nose down to the trachea . 
 common causes include laryngomalacia , vocal cord palsy , subglottic stenosis , tracheal anomaly , laryngeal cleft , vascular and lymphatic malformation , laryngeal papillomas , craniofacial abnormalities and even head and neck tumours . in this paper 
 , we will discuss our approach to infants with stridor including assessment with flexible and rigid endoscopy and treatments to various conditions in a tertiary centre . 
 causes of stridor in infants undergoing rigid laryngotracheobronchoscopy in queen mary hospital , university of hong kong medical centre between 2005 and 2011 will be retrospectively reviewed . 
 treatments according to various conditions will be discussed . 
 successful management of these neonates requires accurate diagnosis , early intervention , and multidisciplinary care by ent surgeons , paediatricians , and paediatric anaesthetists .