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April, 2021
Case of the Month

Clinical History: A 2-month-old male child was found to have a thoracic mass on prenatal ultrasound. Postnatal imaging was consistent with pulmonary sequestration. Computed tomography of the chest showed a 3.9-cm posterior mediastinal mass (Figures 1 and 2) extending into the infra-diaphragmatic region displacing the aorta without luminal compromise. Pulmonary sequestration was felt to be the most likely diagnosis, with retroperitoneal neuroblastoma as the less likely differential diagnostic consideration. The mass was surgically excised. H&E images are shown in Figures 3-6.

Quiz:


Q1. Which of the following germline mutations are seen in type 1 pleuropulmonary blastoma?

  1. STK11
  2. EGFR
  3. DICER1
  4. NCF-1

Q2. Which of the following leisons most commonly contains a type 2 congenital pulmonary airway malformation (CPAM)?

  1. Pulmonary sequestration
  2. Pulmonary hypoplasia
  3. Bronchial atresia
  4. Bronchopulmonary dysplasia

Q3. The presence of mucigenic epithelium in a congenital pulmonary airway malformation is strong evidence of which type of CPAM?

  1. Type 2
  2. Type 1
  3. Type 3
  4. Type 4

Answers to Quiz

Q1. C
Q2. A
Q3. B

Diagnosis

Rhabdomyomatous dysplasia in pulmonary sequestration with type 2 CPAM

Discussion

Chest CT showed a hypodense mass (green arrow) along the medial aspect of the left lower lobe adjacent to the distal descending thoracic aorta (pink arrow) (Figure 1, axial image). The maximum intensity projection (MIP) image shows a small systemic arterial branch (orange arrow) arising from the celiac artery (blue arrow) supplying the mass (green arrow) compatible with pulmonary sequestration (Figure 2, coronal reformatted image). Corresponding histologic sections show bronchiole-like structures lined by columnar epithelial cells with a thin underlying fibromuscular layer (Figures 3-5). The absence of accompanying pulmonary artery branches and the lack of a smooth muscle layer (as would be expected in a true bronchiole) facilitates distinction of these bronchiole-like strcutures from true bronchioles. In addition, there were striated muscle fibers throughout the lesion, representing rhabdomyomatous dysplasia (Figure 6).

Congenital pulmonary airway malformation (CPAM) is the most common type of congenital lung lesion, frequently diagnosed antenatally. Bronchopulmonary sequestration is the most common lesion in the differential diagnosis of CPAM, the former being defined by the absence of a connection to the tracheobronchial tree. In contrast to CPAM, which derives its blood supply from the pulmonary artery, the blood supply of sequestrations is derived from an anomalous systemic artery rather than the pulmonary circulation.

CPAM needs to be distinguished from pleuropulmonary blastoma and may rarely give rise to a mucinous adenocarcinoma (especially type 1 CPAM). The presence of non-neoplastic striated muscle fibers, described as “rhabdomyomatous dysplasia”, is extremely rarely seen in the lung. Associated cardiovascular and/or lung abnormalities have been described. Fraggetta reported striated muscle proliferation in type 2 CPAM and pulmonary sequestration. A rare case of pulmonary rhabdomyomatous dysplasia in a newborn with neurofibromatosis type 1 with no other pulmonary complications has also been described. The origin of striated muscle cells has been proposed as misplaced striated muscle from the pharynx, esophagus or diaphragm (i.e., a developmental error). Others favor the hypothesis of myoblastic differentiation/metaplastic transformation of primitive mesenchymal cells. In our case, neither lethal congenital malformations nor features of neurofibromatosis type 1 were present.

Take home message

Bronchopulmonary sequestrations are defined by systemic artery supply; they may harbor type 2 CPAM and skeletal muscle fibers.

References

Adzick NS, Harrison MR, Crombleholme TM, et al. Fetal lung lesions: management and outcome. Am J Obstet Gynecol 1998;179:884-9.

Fraggetta F, Davenport M, Magro G, Cacciaguerra S, Nash R. Striated muscle cells in non-neoplastic lung tissue: a clinicopathologic study. Hum Pathol 2000;31:1477-81.

Hatanaka K, Yoshioka T, Tasaki T, Tanimoto A. Pulmonary rhabdomyomatous dysplasia of the newborn in neurofibromatosis type 1. Pathol Res Pract 2014;210:318-20.

Leblanc C, Baron M, Desselas E, et al. Congenital pulmonary airway malformations: state-of-the-art review for pediatrician's use. Eur J Pediatr 2017;176:1559-71.

Remberger K, Hübner G. Rhabdomyomatous dysplasia of the lung. Virchows Arch A Pathol Anat Histol 1974;363:363-9.

Contributors

Raghavendra Pillappa, M.D
Assistant Professor of Pathology
Pulmonary Pathologist
Director, Immunohistochemistry
Department of Pathology
Virginia Commonwealth University Health System
Richmond, VA, USA

Shaimaa A Fadl, MBChB
Assistant Clinical Professor
Cardiothoracic Imaging and Emergency Radiology
Department of Radiology
Virginia Commonwealth University Health System
Richmond, VA, USA
2019 PPS Lifetime Achievement Award
Professor Elisabeth Brambilla
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