Right Middle Lobe Syndrome 

  • Author: Nemr S Eid, MD, FAAP, FCCP; Chief Editor: Michael R Bye, MD   more...
 
Updated: Aug 3, 2011
 

Background

Right middle lobe syndrome (RMLS) generally refers to atelectasis in the right middle lobe of the lung. 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-shapLateral 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.

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Pathophysiology

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.

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Epidemiology

Frequency

United States

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

Mortality/Morbidity

Severity in children ranges from mild atelectasis and scarring of no consequence to severe bronchiectasis requiring surgical resection.

Sex

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

Age

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.

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Contributor Information and Disclosures
Author

Nemr S Eid, MD, FAAP, FCCP  Professor of Pediatrics, University of Louisville School of Medicine; Director of Pediatric Pulmonary Medicine, Director of The Childhood Asthma Care and Education Center and the Cystic Fibrosis Center, Medical Director of Pediatric Respiratory Therapy, Kosair Children's Hospital

Nemr S Eid, MD, FAAP, FCCP is a member of the following medical societies: American College of Chest Physicians, American Thoracic Society, Kentucky Medical Association, and Kentucky Pediatric Society

Disclosure: Nothing to disclose.

Coauthor(s)

Michelle Eckerle  University of Louisville School of Medicine

Michelle Eckerle is a member of the following medical societies: Kentucky Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

Thomas Scanlin, MD  Chief, Division of Pulmonary Medicine and Cystic Fibrosis Center, Department of Pediatrics, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School

Thomas Scanlin, MD is a member of the following medical societies: American Association for the Advancement of Science, American Society for Biochemistry and Molecular Biology, American Thoracic Society, Society for Pediatric Research, and Society for Pediatric Research

Disclosure: Nothing to disclose.

Mary L Windle, PharmD  Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Heidi Connolly, MD  Associate Professor of Pediatrics and Psychiatry, University of Rochester; Director, Pediatric Sleep Medicine Services, Strong Sleep Disorders Center

Heidi Connolly, MD is a member of the following medical societies: American Academy of Pediatrics, American Thoracic Society, and Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Mary E Cataletto, MD  Director of Children's Sleep Services, Winthrop Sleep Disorders Center, Mineola, NY; Professor of Clinical Pediatrics, State University of New York at Stony Brook, Stony Brook, NY

Mary E Cataletto, MD is a member of the following medical societies: American Academy of Pediatrics and American College of Chest Physicians

Disclosure: Shering Plough Pharmaceuticals Honoraria Consulting

Chief Editor

Michael R Bye, MD  Professor of Clinical Pediatrics, Division of Pulmonary Medicine, Columbia University College of Physicians and Surgeons; Attending Physician, Pediatric Pulmonary Medicine, Morgan Stanley Children's Hospital of New York Presbyterian, Columbia University Medical Center

Michael R Bye, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Chest Physicians, and American Thoracic Society

Disclosure: Nothing to disclose.

References

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Posteroanterior chest radiograph demonstrating right middle lobe collapse and infiltrate. Note blurred right heart border.
Lateral view chest radiograph showing a wedge-shaped density extending from the hilum anteriorly and inferiorly.
Chest CT scan showing extensive bronchiectasis of both medial and lateral segments of the right middle lobe.
 
 
 
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