Discussion

Nasal airflow obstruction, as occurs in pyriform aperture stenosis, can be potentially life-threatening in neonates. Whilst the exact aetiology of pyriform aperture stenosis is unknown, it is hypothesised to occur because of an overgrowth of the maxillary nasal process during fetal development.^{Reference Belden, Mancuso and Schmalfuss4,Reference Esen, Bayar Muluk, Altintoprak, Ipci and Cingi6,Reference Losken, Burstein and Williams7} Pyriform aperture stenosis can arise alone or in conjunction with a number of craniofacial abnormalities, including a single central maxillary incisor, cleft palate and holoprosencephaly. It often presents in the first hours of life with laboured breathing, respiratory distress, stertor, and cyclical cyanosis that improves with crying.^{Reference Shikowitz1,Reference Lin, Lee, Yang, Hsieh, Su and Sun3}

The diagnosis of pyriform aperture stenosis relies upon otolaryngological examination, with fine-slice CT being the imaging modality of choice. An inability to perform nasoendoscopy because of narrow bony nasal inlets and difficulty passing fine-bore nasogastric tubes through either nostril are key features. There is still no clear consensus on diagnostic criteria using CT imaging. Multiple studies have suggested radiologically measured diagnostic pyriform aperture diameters ranging from less than 3 mm to less than 11 mm.^{Reference Brown, Myer and Manning2,Reference Belden, Mancuso and Schmalfuss4,Reference Osovsky, Aizer-Danon, Horev and Sirota8}

The overall goal of management of pyriform aperture stenosis is to improve nasal airflow and reduce nasal passage obstruction. Traditionally, conservative management strategies entail the use of topical therapies such as nasal saline, decongestants and intranasal steroids, to reduce mucosal size and secretions. Whilst previously used, intranasal Silastic stents have become less favourable, as their small diameter results in frequent occlusion.

The surgical management of pyriform aperture stenosis involves widening of the stenosed pyriform aperture, which can be performed via a number of approaches. The more favourable method is a sublabial endo-oral procedure, utilising burrs to drill away the nasal process of the maxilla, whilst being mindful of the close proximity of the developing tooth buds, the nasolacrimal duct and the infraorbital nerve. This is followed by nasal stent insertion to reduce the incidence of stenosis recurrence or scar-mediated restenosis. Other options include a transnasal approach, which is limited by the increased risk of soft tissue injury, and balloon dilatation of the pyriform aperture.

The challenge of managing pyriform aperture stenosis lies in the difficulty of patient selection for different management options, with clinicians aiming to implement the least invasive treatment required, as many patients will improve with growth. A lack of data on the natural course of pyriform aperture stenosis makes it difficult for clinicians to predict which patients will not improve with conservative management alone.^{Reference Lin, Lee, Yang, Hsieh, Su and Sun3}

There is conflicting evidence on indicators for surgery. In a pooled case series, Wormald et al. demonstrated that a pyriform aperture diameter of 5.7 mm or less was associated with the requirement of surgical intervention.^{Reference Wormald, Hinton-Bayre, Bumbak and Vijayasekaran5} However, subsequent studies found no correlation between degree of stenosis and requirement for surgery, instead suggesting evaluation of the patient's symptoms and progress.^{Reference Lin, Lee, Yang, Hsieh, Su and Sun3,Reference Gonik, Cheng, Lesser, Shikowitz and Smith9} Indications for surgery within these studies were: failure of response to medical treatment, presence of sleep apnoea due to nasal airway obstruction, an inability to insert a 6 French gauge feeding tube, extubation failure, and frequent feeding difficulties with cyanosis. Recently, Moreddu et al. elaborated a management algorithm from their experience of managing 10 patients with pyriform aperture stenosis, which suggests undertaking surgery only in those patients who fail to improve after two weeks of medical therapy.^{Reference Moreddu, Le Treut-Gay, Triglia and Nicollas10}

High-flow nasal cannula treatment is a novel method of respiratory support that delivers humidified and warmed gas to the nasal airways (with or without supplementary oxygen), whilst providing a small degree of positive airway pressure.^{Reference Franklin, Babl, Schlapbach, Oakley, Craig and Neutze11} High-flow nasal cannula therapy improves oxygenation, increases the end-expiratory lung volume, reduces airway resistance, increases functional residual capacity and alveolar recruitment, and flushes nasopharyngeal dead space, thus helping to decrease the work of breathing.^{Reference Ashraf-Kashani and Kumar12} It has been shown to be well tolerated and safe to use in neonates.^{Reference Kotecha, Adappa, Gupta, Watkins, Kotecha and Chakraborty13} A recent study demonstrated a reduction in the rates for requirement of ventilatory therapy escalation with high-flow nasal cannula treatment in neonates with bronchiolitis.^{Reference Franklin, Babl, Schlapbach, Oakley, Craig and Neutze11}

One potential benefit of this treatment over classic nasal mask CPAP is a lack of pressure on the maxilla by the delivery mask, preventing the possible development of acquired midface hypoplasia and nasal trauma. Most recently, the use of high-flow nasal cannula therapy has been described for childhood obstructive sleep apnoea. This is especially valuable in children intolerant of nasal mask CPAP.^{Reference Hawkins, Huston, Campbell and Halbower14–Reference McGinley, Halbower, Schwartz, Smith, Patil and Schneider16} However, high-flow nasal cannula therapy is limited by a relative lack of evidence, and the high cost associated with consumables and acquisition of the device. Given its relatively new use, access to such machines is still limited; indeed, the parents in the above case needed to purchase the device privately.

In the case presented above, the infant experienced significant improvement in overnight breathing on long-term, home-based, high-flow nasal cannula therapy. This resulted in improvements in feeding, development and weight gain, allowing the patient to avoid invasive surgical management. The benefit seen is likely a result of improved delivery of humidified airflow past the anatomical obstruction. This case demonstrates the benefit of long-term high-flow nasal cannula treatment in avoiding surgery for a patient who would have otherwise been a surgical candidate given the degree of pyriform aperture stenosis and initial failure of traditional conservative therapies. With few adverse effects, long-term high-flow nasal cannula therapy may be an attractive new option to prevent invasive surgical management of pyriform aperture stenosis.