Right Middle Lobe Syndrome 

Updated: May 16, 2018
Author: Nemr S Eid, MD, FAAP, FCCP; Chief Editor: Denise Serebrisky, MD 



Right middle lobe syndrome (RMLS) generally refers to chronic or recurrent atelectasis in the right middle lobe of the lung. First described in the medical literature in 1948,[1] it is caused by various etiologies and has no consistent clinical definition. Right middle lobe syndrome is characterized by a wedge-shaped density that extends anteriorly and inferiorly from the hilum of the lung, which is best visualized using lateral chest radiography.

See the image below.

Lateral view chest radiograph showing a wedge-shap Lateral view chest radiograph showing a wedge-shaped density extending from the hilum anteriorly and inferiorly.

This condition is most common in children with a history of asthma or atopy. Although the mechanism by which asthma leads to lobar atelectasis is unknown, associated inflammation, bronchospasm, and secretions that cause mucus plugging are likely major contributors. Management is determined by etiology, and most patients respond to medical therapy alone.


Certain anatomical characteristics make the right middle lobe susceptible to transient obstruction as a result of inflammation or edema. The narrow diameter of the lobar bronchus and acute take-off angle create poor conditions for drainage. Relative anatomical isolation of the middle lobe and poor collateral ventilation decrease the chance of reinflation once atelectasis occurs. Bronchial obstruction can result from extrinsic compression as in hilar lymphadenopathy or tumor of neoplastic origin; however, atelectasis in children usually results from a process such as asthma-associated edema and inflammation. Foreign body aspiration into the right middle lobe orifice can also predispose to collapse of the lobe.



United States

The precise incidence in children is unknown. Right middle lobe syndrome is widely underdiagnosed and frequently unrecognized.


Severity in children ranges from mild atelectasis and scarring of no consequence to severe bronchiectasis requiring surgical resection, although this has become a rarity in the modern era.


Right middle lobe syndrome has been said to occur twice as often in girls than in boys; however, large epidemiologic studies are lacking.


Symptoms begin in early childhood, usually in children aged 1-2 years. Symptom frequency decreases in later childhood, but the interval between onset of symptoms and diagnosis widely varies.




The most common symptoms in right middle lobe syndrome (RMLS) include the following:

  • Persistent or recurrent cough

  • Intermittent wheezing

  • Dyspnea

  • History of recurrent or chronic pneumonia (May often be a misinterpretation of the radiographic findings)

In many cases, these respiratory symptoms are refractory to normal treatment such as antibiotics, antiinflammatory medications, and bronchodilators.

At least half of the patients report a history of asthma or atopy, and one third report a family history of atopy.

Less frequently reported symptoms, which may be indicative of chronic disease with suppurative complications, include the following:

  • Hemoptysis

  • Low-grade fever

  • Fatigue

  • Weight loss

  • Chest pain


Right middle lobe syndrome is essentially a radiographic diagnosis, and physical findings widely vary.

Auscultation of the lungs may reveal a fine wheeze, rales, or diffuse rhonchi, ranging from decreased aeration and dullness to percussion in the region of the right middle lobe. The right middle lobe is anterior, best heard at the nipple. The medial segment is located medial to the nipple; the lateral segment is lateral to the nipple. Failure to listen to this area results in failure to hear the right middle lobe.

Clubbing is rarely found in patients with advanced disease.


Intra-airway origin

In children, right middle lobe syndrome is usually secondary to primary ventilation disorders. Chronic inflammation of the airways, which contributes to atelectasis of the right middle lobe, is present. A paucity of collateral ventilation is observed in children and serves to prevent reinflation.

Primary disorders of ventilation include the following:

  • Asthma

  • Bronchopulmonary dysplasia

  • Chronic pneumonia or bronchitis

  • Cystic fibrosis

  • Other chronic lung diseases caused by aspiration or gastroesophageal reflux

  • Primary ciliary dyskinesia (immotile cilia syndrome)

  • Airway foreign body aspiration 

  • Endobronchial tumors

  • Mucous plugging, as from any of the above

  • Granulation tissue

Extra-airway origin

Extraluminal compression is caused by the following:

  • Cardiovascular anomalies

  • Congenital malformations such as situs inversus and other anatomical defects such as anomalous branching or abnormal diameter, length, or structure of the bronchi

  • Lymphadenopathy of peribronchial nodes

  • Tumors

  • Traction diverticula of the esophagus

Infectious etiologies

See the list below:

  • Whether the infection is a cause of the collapse or a result of airway stasis and poor clearance may not be clear.

  • Primary infectious etiology is more frequent in adults; however, one pediatric study found that 50% of children with collapsed right middle lobe had an underlying bacterial infection.[2]

  • Infectious causes also increase in frequency among immunocompromised patients.

  • Common bacterial causes in children include Streptococcus pneumoniae and Haemophilus influenzae.

  • Fungal causes include histoplasmosis, blastomycosis, and aspergillosis, which manifest as allergic bronchopulmonary aspergillosis (APBA).

  • Mycobacteria, including Mycobacterium tuberculosis, Mycobacterium avium-intracellulare, and Mycobacterium fortuitum have also been identified as causal agents.

  • Occurrence is mainly caused by extrinsic compression by hilar lymph nodes, which are commonly observed in these infections as well as in fungal infections.



Differential Diagnoses



Laboratory Studies

The following studies may be indicated in right middle lobe syndrome (RMLS):

  • Purified protein derivative (tuberculin) skin test

  • CBC count and differential

  • Westergren sedimentation rate

  • Fungal serology by complement fixation and immune diffusion

  • Quantitative immunoglobulins panel

Imaging Studies

Chest radiography with anteroposterior (AP) and lateral views

The classic finding of right middle lobe syndrome is a blurred right heart border and a loss of volume in the right middle lobe (see the image below).

Posterioranterior chest radiograph demonstrating r Posterioranterior chest radiograph demonstrating right middle lobe infiltrate in a 9-year-old male with a history of severe asthma. Note the blurred right heart border.

A wedge-shaped density extending from the hilum anteriorly and inferiorly is best visualized on a lateral view (see the image below).

Lateral view chest radiograph in a 9-year-old male Lateral view chest radiograph in a 9-year-old male with severe asthma showing a wedge-shaped density extending from the hilum anteriorly and inferiorly.

Consolidation and infiltration are less commonly observed.

Acute pneumonia should clear radiologically in 6-8 weeks.

CT scanning

If bronchiectasis is suspected, confirm diagnosis by performing high-resolution chest CT scanning (see the image below), which carries less risk to younger patients or patients with asthma than the seldom-used traditional bronchography. Chest CT scans may also be beneficial in providing information on airway patency and sources of extrinsic compression.[3]  

High-resolution chest CT showing marked chronic ch High-resolution chest CT showing marked chronic changes and volume loss in the right middle lobe with diffuse traction bronchiectasis in 9-year-old male with a history of severe asthma and RML syndrome.

High-resolution chest CT imaging is also helpful for follow-up medical therapy.

Other Tests

Pulmonary function tests (PFTs) can be used to establish a previously unidentified asthmatic component.

When assessing for asthma, a patient's baseline forced expiratory volume in one second (FEV1) may be normal on spirometry.  However, a post-bronchodilator test demonstrating a 10-15% improvement in FEV1, or 25% or greater improvement in FEF25-75% is diagnostic for asthma.[4] In these cases, patients should be treated aggressively per established asthma guidelines.

A study evaluating the usefulness of lung ultrasonography for the diagnosis of neonatal pulmonary atelectasis (NPA) concluded that lung ultrasonography is an accurate and reliable method for diagnosing NPA. This was a study solely in infants. The authors also concluded that lung ultrasonography can find occult lung atelectasis in neonates that could not be detected on chest X-ray.[5]


The value of bronchoscopy is 2-fold, as follows:

  • It is immediately therapeutic in removing mucus and clearing the airway and can be curative in some cases.

  • It allows visualization of the airway and the ability to determine patency of the right middle lobe bronchus and to discern whether endobronchial obstruction is the cause.

Bronchoalveolar lavage can be concurrently performed to determine cellular elements in the right middle lobe. It can also be used to assess the presence of infections by culturing and staining for bacterial, fungal, viral, and mycobacterial pathogens.



Medical Care

Long-term follow-up of children with right middle lobe syndrome (RMLS) shows that most patients do not experience recurrent or persisting symptoms. This indicates that the first line of treatment in all cases is conservative medical management, except in cases involving neoplastic origin and those with bronchiectasis.

Chest physical therapy and postural drainage are the hallmarks of therapy. They may be combined with mucolytics such as nebulized sodium chloride (3% or 7%, based on the patient's age and tolerance), and or dornase alpha to help optimize airway clearance. In persistent or severe cases, especially those with bronchiectasis, patients may benefit from the use of high frequency chest wall oscillation devices.

Treat the asthmatic child with aggressive anti-inflammatory therapy such as inhaled steroids. Consider systemic steroids. Guidelines for the diagnosis and management of asthma have been established.[6]

Provide the patient with chest physical therapy and postural drainage. In unresponsive patients or patients who have a predisposition to airway colonization, an appropriate antibiotic, as determined by a bronchoalveolar lavage (BAL) culture, should be added to their regimen.

Patients with fungal infections (eg, histoplasmosis) or tuberculous infections who have hilar adenopathy and complete blockage of their right middle lobe should be treated aggressively. The addition of systemic corticosteroids may be necessary.

Surgical Care


Lobectomy is indicated in cases of malignancy and bronchiectasis that are unresponsive to medical therapy.

Only perform lobectomy when right middle lobe syndrome is associated with systemic symptoms such as failure to thrive, persistent cough, and recurrent fever or when chronic infection threatens the remainder of the lung. The majority of patients with appropriate aggressive medical therapy will rarely require surgical intervention. 


Avoid bronchography because of potential risks to the patient unless surgery is seriously considered; therefore, always explore high-resolution CT imaging as an alternative.


Consultations may include a pediatric pulmonologist and/ or a pediatric infectious disease specialist.



Medication Summary

The role of antibiotic therapy in the treatment of right middle lobe syndrome (RMLS) is not well studied. Antibiotics are usually administered during acute exacerbations and when bronchiectasis is well established. In this latter instance, long-term rotation of antibiotics (ie, 3 weeks on and 1 week off, then change antibiotic) is advocated. Base the choice of antibiotic on culture and sensitivity results of either sputum or bronchoalveolar lavage (BAL) fluid. When this is not available, select a broad-spectrum antibiotic to cover S pneumoniae, other streptococci, H influenzae, and Moraxella catarrhalis. Antibiotics can be orally or intravenously administered. The use of nebulized antibiotics has not been studied in right middle lobe syndrome. Also see Asthma for relevant treatment information. From the authors experience, the use of Azithromycin given three times per week can be helpful in the treatment of established bronchiectasis. 


Class Summary

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.

Cefuroxime (Ceftin, Zinacef)

Second-generation cephalosporin maintains gram-positive activity that first-generation cephalosporins have; adds activity against Proteus mirabilis, H influenzae, Escherichia coli, Klebsiella pneumoniae, and M catarrhalis.

Cefpodoxime proxetil (Vantin)

Inhibits bacterial cell wall synthesis by binding to one or more of the penicillin-binding proteins; bacteria eventually lyse because of ongoing activity of cell wall autolytic enzymes while cell wall assembly is arrested.

Cefprozil (Cefzil)

Binds to one or more of the penicillin-binding proteins, which, in turn, inhibits cell wall synthesis and results in bactericidal activity.

Erythromycin and sulfisoxazole (Pediazole)

Erythromycin is a macrolide antibiotic with a large spectrum of activity. Erythromycin binds to the 50S ribosomal subunit of the bacteria, which inhibits protein synthesis.

Sulfisoxazole expands erythromycin's coverage to include gram-negative bacteria. Sulfisoxazole inhibits bacterial synthesis of dihydrofolic acid by competing with para-aminobenzoic acid.

Azithromycin (Zithromax)

Inhibits bacterial growth, possibly by blocking dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest.

Clarithromycin (Biaxin)

Inhibits bacterial growth, possibly by blocking dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest.

Amoxicillin and clavulanic acid (Augmentin)

Drug combination treats bacteria resistant to beta-lactam antibiotics. For children >3 months, base dosing protocol on amoxicillin content. Due to different amoxicillin/clavulanic acid ratios in 250-mg tab (250/125) vs 250 mg chewable-tab (250/62.5), do not use 250-mg tab until child weighs >40 kg.

Sulfamethoxazole and trimethoprim (Bactrim, Septra, Cotrim)

Inhibits bacterial growth by inhibiting synthesis of dihydrofolic acid.



Further Outpatient Care

Periodic office follow-up with repeat chest radiographs, and pulmonary function testing when applicable is warranted to assess response to medical therapy. Periodic assessment of caregivers' chest physical therapy techniques can be monitored during the visits as well.

Further Inpatient Care

Most patients with right middle lobe syndrome (RMLS) are managed as outpatients; however, acute exacerbations may require inpatient care and intravenous antibiotics.


Prevention of right middle lobe syndrome has not been studied, but, because of the long-term morbidity associated with this condition, perform a repeat chest  radiograph in children with asthma who have atelectasis of the right middle lobe during an acute asthma exacerbation and in children with acute pneumonia of the right middle lobe to document resolution. This should be done at least 6 to 8 weeks after the initial occurrence.

In one report, a more aggressive approach in a cohort of 55 symptomatic children with right middle lobe syndrome followed for a median duration of 2 years yielded good outcome.[7] All these children underwent flexible bronchoscopy at presentation, and specific antibiotic therapy was given based on bronchial alveolar lavage fluid. Bronchiectasis was documented in 27% of patients, and the duration of symptoms correlated with the development of this unfavorable complication.


Long-term complications range from none to minimal pulmonary scarring of no discernible physiological consequence to severe bronchiectasis requiring surgical intervention.

In children with asthma, right middle lobe syndrome may produce a vicious cycle of infection, inflammation, and asthma exacerbation.


Historically, right middle lobe syndrome has been reported to resolve in approximately 33% of children after bronchoscopy. Approximately 33% recover eventually with medical management, 22% require lobectomy, and 11% have decreased severity of symptoms but should be monitored for the possibility of requiring lobectomy later. While recent published data is lacking, with aggressive modern therapy as outlined above, it is more likely that the number of patients requiring lobectomy is far lower. In our own experience spanning thirty years, lobectomy was performed only once due to frequent recurrent pulmonary infections and failure to gain weight. 

About one third of patients with right middle lobe syndrome in early childhood continue to have symptoms in later childhood. These patients usually experience asthma symptoms or another chronic lung condition such as cystic fibrosis. A recent study examined the efficacy of early postnatal corticosteroids for preventing chronic lung disease in preterm infants.[8]

The remaining two thirds of children with right middle lobe syndrome do not have persistent symptoms later in adulthood.

Patient Education

Because chest physical therapy and postural drainage are of paramount importance in the management of RMLS, instruct the caretaker with appropriate techniques and position for right middle lobe physiotherapy. This is often performed by a registered respiratory or physical therapist. Regardless, the therapist should be somebody who frequently deals with children.

Flutter valve and high-frequency oscillation (known as the vest) have not been studied in this setting, but they may be alternative modalities of delivering chest physical therapy.