Anomalous intrapulmonary course of azygos vein that creates accessory fissure
Includes 4 layers of non-fused parietal and visceral pleura (mesoazygos) invaginated into medial right upper lobe (RUL)
Vertical or curved oblique course of fissure
Teardrop-shaped lower margin contains azygos vein
Trigone
Cranial aspect of fissure (triangular shape); determines size of lung medial to fissure
Included lung shape classified based on trigone position
Type A: Trigone located in lateral aspect of pulmonary apex
Type B: Trigone located at mid point of apex; fissure is relatively vertically oriented
Type C: Trigone located medially; fissure curves toward mediastinum
Fissure length varies with type: Longer in type A, shorter in types B and C
Accessory fissure of variable size borders medial aspect of RUL
IMAGING
Imaging Recommendations
Radiographic Findings
CT Findings
DIFFERENTIAL DIAGNOSIS
PATHOLOGY
General Features
CLINICAL ISSUES
Presentation
Demographics
DIAGNOSTIC CHECKLIST
Image Interpretation Pearls
Selected References
Bostanci K et al: Variations in pulmonary fissural anatomy: a medicolegal autopsy study of 256 cases. ANZ J Surg. 90(4):608-11, 2020
Semionov A et al: Migration of the azygos vein from the azygos fissure to the mediastinum. Radiol Case Rep. 14(6):763-5, 2019
Taydas O et al: Reentrance of azygos vein into azygos fissure after pneumothorax. Eurasian J Med. 49(1):62-3, 2017
Suwatanapongched T et al: Visibility and variability of pleural fissures on normal digital chest radiographs of 1,000 healthy adults. Jpn J Radiol. 33(4):201-9, 2015
Lenoir V et al: The empty azygos fissure. J Radiol Case Rep. 7(4):10-5, 2013
Villanueva A et al: Migrating azygos vein and vanishing azygos lobe: MDCT findings. AJR Am J Roentgenol. 194(3):599-603, 2010
Maldjian PD et al: The empty azygos fissure: sign of an escaped azygos vein. J Thorac Imaging. 23(1):54-6, 2008
Hayashi K et al: Radiographic and CT appearances of the major fissures. Radiographics. 21(4):861-74, 2001
Shin MS et al: Clinical significance of azygos vein enlargement: radiographic recognition and etiologic analysis. Clin Imaging. 23(4):236-40, 1999
Caceres J et al: The azygos lobe: normal variants that may simulate disease. Eur J Radiol. 27(1):15-20, 1998
Related Anatomy
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References
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Tables
KEY FACTS
Terminology
Imaging
Top Differential Diagnoses
Pathology
Clinical Issues
Diagnostic Checklist
TERMINOLOGY
Synonyms
Azygos fissure
Definitions
Anomalous intrapulmonary course of azygos vein that creates accessory fissure
Includes 4 layers of non-fused parietal and visceral pleura (mesoazygos) invaginated into medial right upper lobe (RUL)
Vertical or curved oblique course of fissure
Teardrop-shaped lower margin contains azygos vein
Trigone
Cranial aspect of fissure (triangular shape); determines size of lung medial to fissure
Included lung shape classified based on trigone position
Type A: Trigone located in lateral aspect of pulmonary apex
Type B: Trigone located at mid point of apex; fissure is relatively vertically oriented
Type C: Trigone located medially; fissure curves toward mediastinum
Fissure length varies with type: Longer in type A, shorter in types B and C
Accessory fissure of variable size borders medial aspect of RUL
IMAGING
Imaging Recommendations
Radiographic Findings
CT Findings
DIFFERENTIAL DIAGNOSIS
PATHOLOGY
General Features
CLINICAL ISSUES
Presentation
Demographics
DIAGNOSTIC CHECKLIST
Image Interpretation Pearls
Selected References
Bostanci K et al: Variations in pulmonary fissural anatomy: a medicolegal autopsy study of 256 cases. ANZ J Surg. 90(4):608-11, 2020
Semionov A et al: Migration of the azygos vein from the azygos fissure to the mediastinum. Radiol Case Rep. 14(6):763-5, 2019
Taydas O et al: Reentrance of azygos vein into azygos fissure after pneumothorax. Eurasian J Med. 49(1):62-3, 2017
Suwatanapongched T et al: Visibility and variability of pleural fissures on normal digital chest radiographs of 1,000 healthy adults. Jpn J Radiol. 33(4):201-9, 2015
Lenoir V et al: The empty azygos fissure. J Radiol Case Rep. 7(4):10-5, 2013
Villanueva A et al: Migrating azygos vein and vanishing azygos lobe: MDCT findings. AJR Am J Roentgenol. 194(3):599-603, 2010
Maldjian PD et al: The empty azygos fissure: sign of an escaped azygos vein. J Thorac Imaging. 23(1):54-6, 2008
Hayashi K et al: Radiographic and CT appearances of the major fissures. Radiographics. 21(4):861-74, 2001
Shin MS et al: Clinical significance of azygos vein enlargement: radiographic recognition and etiologic analysis. Clin Imaging. 23(4):236-40, 1999
Caceres J et al: The azygos lobe: normal variants that may simulate disease. Eur J Radiol. 27(1):15-20, 1998
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