Focal lung hyperinflation in an infant: Not always congenital lobar hyperinflation - A case report

INTRODUCTION

In children, lymphadenopathy is a key indicator of tuberculosis (TB) on radiological imaging.^[1] Lymphobronchial TB arises when TB infection in mediastinal lymph nodes extends to the airways, resulting in airway obstruction due to lymph node enlargement and associated complications.^[2] This condition predominantly affects the right main bronchus or bronchus intermedius, leading to luminal narrowing and subsequent complications.^[1] Obstruction can cause a ball-valve effect, trapping air in the affected lung segments and leading to consolidation or “drowned lung” when the bronchi are completely occluded.^[1,3] Radiological manifestations of lymphobronchial TB include collapse, expansile pneumonia, necrotizing pneumonia, and cavitation due to obstruction-related complications.^[1] Children, due to their smaller and more compressible airways, are particularly at risk for lymphobronchial TB, making this condition almost exclusive to the pediatric population.^[1] Recognizing lymphobronchial TB and its parenchymal complications on computed tomography (CT) scans can guide appropriate interventions to alleviate airway obstruction and potentially save lung function.^[3]

CASE REPORT

A 1-year-old female presented with intermittent cough, respiratory distress, and fever for the past 3 months, with a documented history of recurrent nebulization since 3 months of age. There was clinical worsening over the last few days, and the child presented in respiratory distress. On clinical assessment, the child was hemodynamically stable. Her heart rate and respiratory rate were elevated, measuring 150 beats/min and 60 breaths/min, respectively. The oxygen saturation was recorded at 88% while in ambient air and improved to 94% with supplemental oxygen administered at a flow rate of 4 L/min. Auscultation revealed the presence of bilateral rhonchi and a significant reduction in air entry observed on the right side. She also exhibited signs of pallor, frontal bossing, and widening of the wrists. The chest radiograph [Figure 1] demonstrated focal hyperlucency within the right mid-zone and upper zone, accompanied by mass effect and contralateral mediastinal shift. In light of these findings, the differential diagnoses considered included congenital lobar overinflation and foreign body aspiration. However, the long duration of symptoms was atypical for foreign body aspiration, while the child’s age was on the higher side for congenital lobar hyperinflation (most of these cases present by 6 months of age).

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Figure 1:

The frontal chest radiograph reveals a localized area of hyperlucency within the right mid and upper zones (yellow star), accompanied by mass effect and contralateral shift of the mediastinum.

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Contrast-enhanced CT of the chest was done for further evaluation. It revealed hyperinflation of the right middle lobe [Figure 2] and patchy areas of collapse/consolidation in the right as well as left upper lobes. There were some small areas of overinflation affecting the right lower lobe as well [Figure 3]. The presence of a definite intraluminal foreign body was not identified; thus, congenital lobar hyperinflation was deemed the most probable diagnosis. A few enlarged lymph nodes were seen in the right paratracheal and precarinal region [Figure 3]; these were thought to possibly represent a superadded infection.

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Figure 2:

(a) Axial lung window CT image above the level of carina shows patchy areas of collapse in bilateral upper lobes. (b) Axial lung window, (c) coronal lung window and (d) sagittal lung window CT images show hyperinflation of the right middle lobe (yellow stars).

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Figure 3:

(a) Axial mediastinal window section shows right paratracheal lymphadenopathy (short white arrow), with areas of heterogeneous enhancement. (b) Axial mediastinal window section shows enlarged pre-carinal lymph nodes causing extrinsic impression on the carina (yellow circle). (c) Thin lung window section reveals subtle intraluminal opacities within the middle lobe bronchi (long white arrow). (d) Thin lung window section shows small areas of overinflation in the right lower lobe (yellow star).

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A bronchoscopy was then performed, which revealed that the right upper lobe bronchus was angulated superiorly, while the right middle lobe bronchus exhibited granulation tissue that nearly occluded the lumen. The right lower lobe bronchus and the left-sided airway were normal. Granulation tissue sampling confirmed the presence of acid-fast bacilli. The child was started on anti-tubercular medication. However, she unfortunately succumbed to her illness.

On re-evaluation of thin lung window sections, the medial and lateral segmental bronchi of the right middle lobe exhibited several subtle, partially occlusive intraluminal densities [Figure 3]. Thus, subtle intraluminal pathology was retrospectively identified on thin CT sections, which had previously been overlooked. Figure 4 depicts the timeline of the patient’s clinical course, diagnostic procedures, and treatment outcome.

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Figure 4:

Chronological flowchart showing the patient’s clinical course, diagnostic interventions, and treatment outcome.

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DISCUSSION

Lymphobronchial TB represents a distinctive manifestation of pediatric pulmonary TB, characterized by involvement of the mediastinal lymph nodes and subsequent airway involvement. Although pediatric TB itself remains a significant global health issue, accounting for approximately 10–15% of the total TB burden worldwide according to the World Health Organization, lymphobronchial TB as a specific entity is reported less frequently in the literature.^[4] Various series and case reports estimate the prevalence of lymphobronchial TB in children with pulmonary TB to vary widely, ranging from 10% to 30% depending on the geographic region and diagnostic modality used.^[1]

The relative rarity of lymphobronchial TB is partly attributed to diagnostic challenges due to subtle clinical and radiological manifestations, often leading to misinterpretation as other causes of airway obstruction, such as congenital lobar hyperinflation or foreign body aspiration. Reports also emphasize that lymphobronchial TB is predominantly seen in infants and young children, reflecting the vulnerability of their smaller, more compressible airways to lymph node-induced obstruction.

This case is noteworthy because it highlights the diagnostic complexity when lymphobronchial TB presents with focal lung hyperinflation mimicking congenital lobar overinflation and lacking some of the classical imaging features, such as necrotic lymphadenopathy and cavitation. Such presentations remain underreported in the current literature, underscoring the importance of heightened clinical suspicion and detailed imaging assessment to avoid delayed diagnosis and management.

Lymphobronchial TB usually affects young children, particularly infants, due to the small caliber of their airways.^[3] Both the involvement of the airway and the enlargement of lymph nodes contribute to the term “lymphobronchial.”^[1-3] Airway narrowing may arise from an extraluminal source attributable to enlarged lymph nodes, or there may be an intramural or intraluminal component contributing to the obstruction.^[1,2,5]

Inflammatory processes may affect the bronchial wall, leading to caseation and intraluminal granulation tissue, which subsequently induces secondary complications, such as bronchial collapse, distal lung consolidation, cavitation, and potentially hyperinflation of the lung tissue.^[1,2,3,5]

Airway narrowing may be detected on chest radiographs in children with pulmonary TB. Infants are at higher risk of developing airway narrowing (double) as compared to older children, due to smaller caliber of airways and lesser cartilage support.^[6]

Contrast-enhanced CT enables comprehensive imaging evaluation of suspected cases, as it is able to demonstrate lymph nodal enlargement and better depict the site and severity of airway narrowing. Presence of centrally necrotic lymph nodes, if seen, is highly suggestive of tubercular lymphadenopathy – although it may not be seen in all cases. The most common sites of lymphadenopathy include the subcarinal, right hilar, and paratracheal locations, and the majority of cases show lymphadenopathy at more than one location.^[1,7] While performing CT, it should be ensured that pediatric CT protocols should be used, in which the radiation dose is tailored according to the age and weight of the child, and the as low as reasonably achievable principle is applied to limit radiation dose. Usually, as CT scan times are less, respiratory gating is not required, and images of adequate diagnostic quality can be acquired with the child breathing normally, after sedation.

For airway evaluation, thin-section CT lung window images and minimum intensity projection images are useful. The presence, multifocality, and severity of airway assessment should be evaluated by assessment of airway diameter at the site of maximum stenosis. Common sites of airway narrowing include the bronchus intermedius and the left main bronchus.^[1]

CT also demonstrates associated parenchymal changes such as collapse, air trapping, consolidation, and nodules. The presence of consolidation, atelectasis, or air-trapping indicates reversible lung injury. Air bronchograms or fluid bronchograms may be seen, and expansile pneumonia may give the appearance of mass-like consolidation on CT. The affected lung may show absence of enhancement and areas of cavitation and parenchymal destruction – this indicates irreversible injury and non-salvageable lung, which may require lobectomy/surgery.^[3]

Our case underscores that lymphobronchial TB should always be considered in the differential diagnosis of intrathoracic airway obstruction in infants and small children, especially in a child with fever and a relatively long history. In our case, the clinical presentation of intermittent cough and fever, along with a history of recurrent nebulization and, ultimately, respiratory distress, was non-specific. The findings from the chest radiograph were limited to focal hyperlucency, suggesting air-trapping, which raised initial suspicion for congenital lobar overinflation or foreign body aspiration. No areas of consolidation or lung nodules, or obvious lymphadenopathy were visible on the chest radiograph.^[7]

Once CT was performed, the possibility of foreign body aspiration was excluded. Small enhancing lymph nodes were detected on CT, while intraluminal granulation tissue within the affected bronchi was subtle and missed initially. The presumptive CT diagnosis remained congenital lobar hyperinflation, as other findings supporting the imaging diagnosis of TB – like necrotic lymphadenopathy, consolidation with cavitation or tree-in-bud nodules – were absent in this case.

Bronchoscopy allowed for direct visualization of the airway and facilitated the sampling of granulation tissue, leading to the confirmation of TB. Endobronchial ultrasound-guided transbronchial fine-needle aspiration has been shown to be a safe modality for sampling of mediastinal lymphadenopathy in children. Although invasive, this may be useful to diagnose cases of lymphobronchial TB. This highlights the importance of invasive diagnostic procedures in pediatric patients, particularly when non-invasive imaging and clinical assessments yield inconclusive results.

The cases of lymphobronchial TB are managed with anti-tubercular treatment. Concomitant steroids may be helpful in overtly symptomatic cases, early in the course of the disease. Interventional bronchoscopic techniques and surgery may be required in select patients with severe tracheobronchial stenosis causing significant symptoms, including dyspnea, repeated post-obstructive pneumonia, or bronchiectasis.

DIFFERENTIAL DIAGNOSIS (FOCAL AIR-TRAPPING)

1. Congenital lobar overinflation

2. Foreign body aspiration

   Another differential diagnosis to consider in a case of focal lung hyperinflation or air-trapping in infants and young children, besides congenital lobar overinflation and foreign body aspiration, is contralateral lung hypoplasia.

3. Contralateral lung hypoplasia

   Contralateral lung hypoplasia is a developmental anomaly where one lung is underdeveloped, which can cause compensatory hyperinflation or overexpansion of the opposite lung.

This can mimic focal hyperinflation on imaging because the relatively smaller lung volume on one side causes the other lung to appear overinflated.

On chest radiograph, it may be sometimes difficult to determine which side is abnormal. As a rule, the side showing definite features of volume loss, like rib crowding, is likely to be the abnormal side. Furthermore, in cases with unilateral hypoplasia and contralateral compensatory over-inflation, lung vascularity is usually normal on the side with compensatory hyperinflation. Confirmation may require a detailed imaging assessment, using CT, to visualize lung volumes and bronchial anatomy.

Unlike lymphobronchial TB, lung hypoplasia is congenital without inflammatory lymphadenopathy or airway granulomas, and associated mediastinal shifts correspond to volume loss rather than mass effect or obstruction.

CONCLUSION

CT plays a key role in diagnosing lymphobronchial TB in children and planning appropriate care. However, findings on CT may be subtle and may not always be diagnostic. Thus, lymphobronchial TB should always be considered in the differential diagnosis of intrathoracic airway obstruction in infants and small children, especially in a child with fever and a relatively long history.

TEACHING POINTS

1. Lymphobronchial TB occurs due to airway involvement in children with TB and mediastinal lymphadenopathy.

2. Airway involvement in TB is most common in infants and small children due to the smaller caliber and increased compressibility of airways. Common sites of narrowing include the bronchus intermedius and the left main bronchus.

3. Chest radiographs may show enlarged lymph nodes, airway narrowing, or parenchymal abnormality.

4. CT can better depict the lymph nodal enlargement, airway abnormality, as well as parenchymal changes secondary to airway obstruction. These include changes suggestive of reversible lung injury – like consolidation with air bronchogram, expansile pneumonia with fluid bronchograms, atelectasis or air-trapping; as well as features of irreversible lung injury – non-enhancing lung with cavitation and parenchymal destruction.

MCQs

1. Airway obstruction in lymphobronchial TB may occur as a result of pathology localized to which part of the airway?

   1. Intraluminal

   2. Extraluminal

   3. Intramural

   4. All of the above

   Answer key: d

2. To depict airway narrowing on CT, what reconstructions are helpful?

   1. Maximum intensity projection (MIP)

   2. Minimum intensity projection (MinIP)

   3. Both a and b

   4. Neither a nor b

   Answer key: b

3. What statement is TRUE about congenital lobar hyperinflation?

   1. Usually affects a single lobe

   2. Commonly diagnosed in children older than 1 year

   3. Lower lobes are the most commonly affected

   4. CT shows aberrant vascular supply to the affected region in all cases

   Answer key: a

4. Reversible parenchymal changes in lymphobronchial TB include ALL EXCEPT

   1. Consolidation with air bronchogram

   2. Air-trapping

   3. Atelectasis

   4. Non-enhancing, cavitated areas of lung parenchyma

   Answer key: d