Diffuse pulmonary interstitial emphysema in a late preterm neonate without mechanical ventilation

Introduction

Pulmonary interstitial emphysema (PIE) is most commonly seen in the setting of preterm, low birth weight neonates with lung disease. PIE is typically a transient phenomenon, but can also develop into persistent PIE when lasting longer than 1 week and can cause mass effect with respiratory distress [1]. PIE is thought to be on the same spectrum of conditions as pneumothorax and pneumomediastinum. However, PIE is rarely reported without mechanical ventilation [2]. We report a case of diffuse PIE in a late preterm neonate without mechanical ventilation, complicated by bilateral pneumothoraces. The neonate was also found to have congenital thyroid aplasia.

Case presentation

The patient is a 3000 g product of a 37 weeks and 4 days' pregnancy, born to a 34-year-old G2P2002 mother via spontaneous vaginal delivery. Pregnancy and delivery were complicated by maternal cholestasis. There was one turn of a tight nuchal cord at the time of delivery which required cutting. The neonate’s APGAR scores were 8 and 8. The neonate developed grunting and retractions at 5 min of life, with an oxygen saturation of 70%, and was resuscitated with nasal continuous positive airway pressure (CPAP) at 5 mm Hg and 70% inspired oxygen. This was then titrated to 40% with the oxygen saturation at 94%.

In the neonatal intensive care unit (NICU), the chest X-ray (CXR) demonstrated rounded and linear lucencies over the left lower lung at 12 h, extending to the entire right and left lungs at 24 h after birth (Figure 1). CPAP pressure was increased to 7 mm Hg due to persistent retractions. The neonate was intubated after 1 day of life due to persistently increased work of breathing, with initial minute ventilation of 20 breaths with 5 mL/kg, intermittent mandatory ventilation of 20 per min and FiO₂ of 40%. The neonate was extubated on day 3 of life.

Figure 1:

Chest radiograph of the neonate 24 h after birth. Linear and rounded lucencies are noted over the entire right and left lung.

On day 4 of life, the neonate was noted to have bradycardia to 70 beats per minute (bpm), oxygen saturation at 50% without breath sounds over the left thorax and positive transillumination. An emergent chest tube was placed on the left with improvement of oxygen saturation to >95% and heart rate to >120 bpm. CXR initially confirmed a left-sided pneumothorax (Figure 2); but after development of further desaturation, an urgent repeat CXR then showed a new right-sided pneumothorax. A right-sided pigtail catheter was placed, again with improvement of desaturation to >95% (Figure 3).

Figure 2:

Chest radiographs of the neonate on day 4 of life, obtained due to sudden desaturation and bradycardia.

The left lateral decubitus (A) and supine (B) radiographs demonstrate a left sided pneumothorax. The inserted chest tube is also seen

Figure 3:

A repeat set of chest radiographs obtained later on day 4 of life due to another episode of sudden desaturation and retraction. A right-sided pneumothorax is now seen (A) as a peripheral lucency. A right chest tube was placed (B), later replaced by a pigtail catheter.

Newborn screening returned an abnormally elevated thyroid stimulating hormone of 269 and free thyroxine (T4) of 0.22. The patient was initiated on 37.5 μg of levothyroxine daily. Anti-thyroid peroxidase and thyroglobulin antibody tests were negative. A nuclear medicine scan demonstrated no tissue uptake of radionuclide suggesting congenital aplasia (Figure 4). The patient’s hospital course was also complicated by hyponatremia, which subsequently resolved, and was thought to be due to a combination of lung pathology and congenital hypothyroidism. The patient tolerated clamping and removal of the left-sided pigtail catheter at 8 days of life, and removal of the right-sided pigtail catheter at 13 days of life.

Figure 4:

An anterior and left lateral projection of a thyroid nuclear medicine scan after injection of 0.769 mCi of technetium-99m performed on day 16 of life. The imaging demonstrates no radiotracer uptake in the neck or chest, confirming the clinical diagnosis of congenital thyroid aplasia.

Discussion

PIE occurs due to dissection of air into the interstitium of the lung parenchyma, with the possibility of extension into the pleura or mediastinum, causing pneumothorax and pneumomediastinum, respectively [1]. It has been well described that mechanical ventilation predisposes neonates to this condition [3]. Recent studies suggest that airway overload, or volutrauma, rather than pressure overload, or barotrauma, produces this type of injury [4]. Other predisposing factors include respiratory distress syndrome (RDS), lower birth weight and maternal exposure to magnesium sulfate for tocolysis [5].

PIE has been rarely reported in neonates without mechanical ventilation [6], [7], [8], [9], [10], [11]. The previously reported cases of PIE are localized, contrasted by our case, which presented with diffuse, bilateral PIE. These cases share the commonality of CPAP, which was utilized in these cases for respiratory distress. PIE has also been reported in neonates without any respiratory support such as mechanical ventilation or CPAP, but these cases remain localized, instead of the diffuse bilateral presentation in our case [12], [13].

PIE is associated with a significant increase in mortality and often presents with a distinct clinical picture such as retractions, tachypnea and increased oxygen requirements, before radiographic findings present. These findings were observed in our patient prior to development of PIE, as well as before each instance of pneumothorax [14]. Our patient was symptomatic, prior to evidence of PIE and pneumothorax. Given that PIE often occurs in lower birth weight, preterm neonates, other complications such as meningitis should not be ignored [15].

Currently, we are unaware of any association between PIE and congenital hypothyroidism, and our patient may be a case of an unhappy coincidence.

On imaging, chest radiographs of acute PIE (defined as less than 1 week of duration) showed tubular and cystic lucencies that do not conform to the typical branching pattern of the tracheobronchial tree [4]. A multi-institutional study of 17 patients with PIE reported the following computed tomography (CT) findings of PIE as hyperexpanded cystic radiolucencies with multiple, thin-walled cysts. The majority of these CT cases also demonstrated a characteristic line-and-dot pattern [1]. Non-surgical management can be attempted in cases of PIE, with surgical resection reserved for the patient with persistent PIE (defined as lasting longer than 1 week) [1].

In conclusion, PIE is a condition caused by volutrauma which is more commonly seen in preterm infants on mechanical ventilation. It may rarely present in neonates with nasal CPAP. We report a case of diffuse bilateral PIE, which subsequently developed into bilateral pneumothoraces. Although our patient also presented with congenital hypothyroidism, causal relationship between these two conditions, if any, is unclear.