Trigonum parietale (azygos lobe)
Citation, DOI & article data
The trigonum parietale refers to a triangular opacity seen on chest radiograph that correlates with a small piece of extrapleural areolar tissue that lies between the layers of pleura in the fissure of an azygos lobe 1-4. It may be seen at the most superior portion of the azygos fissure and should not be confused with the azygos vein that is usually present at the inferior end of the fissure as a radio-opaque tear shape 2.
The location of the trigonum parietale determines the size of the azygos lobe, which would include a laterally placed trigonum parietale in a larger azygos lobe and a more medial placement in a smaller lobe 5.
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- 2. Copley, S, Hansell, D, & Kanne, J 2014, Thoracic Imaging : Illustrated Clinical Cases, Second Edition, Taylor & Francis Group, London. ISBN: 9781482231168
- 3. Rivaud, Y. & Maldjian, P. D. (2019). The Azygos Vein From A to Z. Journal of Thoracic Imaging, 34 (5), W100-W108. doi:10.1097/RTI.0000000000000420
- 4. Jamal Akhtar, Amos Lal, Kevin B. Martin, Joel Popkin, Azygos lobe: A rare cause of right paratracheal opacity, Respiratory Medicine Case Reports, Volume 23, 2018, Pages 136-137, ISSN 2213-0071, doi:10.1016/j.rmcr.2018.02.001
- 5. Cáceres J, Mata JM, Alegret X, Palmer J, Franquet T. Increased density of the azygos lobe on frontal chest radiographs simulating disease: CT findings in seven patients. AJR Am J Roentgenol. 1993 Feb;160(2):245-8. doi:10.2214/ajr.160.2.8424325