Incidentally detected rare normal anatomical variation of the hemiazygous venous system on computed tomography thorax

Abhang Apte; Sarvesh Patil; Devidas B Dahiphale; Sambhaji Pawal; Asmita Suryawanshi; Prasanna Mishrikotkar

doi:10.4103/0971-9903.189527

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CASE REPORT

Year : 2016 | Volume : 21 | Issue : 2 | Page : 133-135

Incidentally detected rare normal anatomical variation of the hemiazygous venous system on computed tomography thorax

Abhang Apte, Sarvesh Patil, Devidas B Dahiphale, Sambhaji Pawal, Asmita Suryawanshi, Prasanna Mishrikotkar
Department of Radiology, MGM Medical College, Aurangabad, Maharashtra, India

Date of Web Publication

31-Aug-2016

Correspondence Address:
Abhang Apte
Department of Radiology, MGM Medical College, Aurangabad, Maharashtra
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/0971-9903.189527

Abstract

Various normal anatomical variations of azygous and hemiazygous venous system have been described. We report computed tomography features of incidentally detected anatomical variation of the hemiazygous venous system in a patient with interstitial lung disease. The knowledge of normal anatomical variations of the hemiazygous and accessory hemiazygous venous system is important for both to the reporting radiologist as well as the operating surgeon.

Keywords: Anatomical variants, azygous, computed tomography, hemiazygous

How to cite this article:
Apte A, Patil S, Dahiphale DB, Pawal S, Suryawanshi A, Mishrikotkar P. Incidentally detected rare normal anatomical variation of the hemiazygous venous system on computed tomography thorax. J Mahatma Gandhi Inst Med Sci 2016;21:133-5

How to cite this URL:
Apte A, Patil S, Dahiphale DB, Pawal S, Suryawanshi A, Mishrikotkar P. Incidentally detected rare normal anatomical variation of the hemiazygous venous system on computed tomography thorax. J Mahatma Gandhi Inst Med Sci [serial online] 2016 [cited 2023 Mar 29];21:133-5. Available from: https://www.jmgims.co.in/text.asp?2016/21/2/133/189527

Introduction

The azygous venous system is a collective term given to azygous, hemiazygous, and accessory hemiazygous veins. The hemiazygous vein and the accessory hemiazygous vein are seen on the left side, and the azygous vein is seen on the right side in relation to the vertebral column. Both the hemiazygous and accessory hemiazygous veins drain into the azygous vein.^[1],[2] Anatomical variations of the azygous venous system are not uncommon.^[3],[4] Contrast computed tomography (CT) with reformatted images helps in accurate and rapid noninvasive evaluation of anatomical details.

Case Report

A 62-year-old man presented with complaints of nonproductive cough and progressive breathlessness in Department of Respiratory Medicine. Pulmonary function tests showed an abnormal restrictive pattern; hence, the patient was advised CT scan for better assessment of pulmonary pathology.

Contrast-enhanced CT thorax was done using 16 slice multi row detector CT scan (Toshiba, Aquilion). Pre contrast CT thorax revealed sub pleural thickening with ground glass opacities with adjacent areas of bronchiectasis and honeycombing more in apicoposterior and posterobasal segments of lungs suggestive of usual interstitial pneumonia. Contrast study was done using intravenous nonionic contrast medium. Maximum intensity projections (MIPs) and volume rendering technique (VRT) reformations were done for better anatomical assessment.

Incidental finding was a continuation of the left hemiazygous vein into the accessory hemiazygous vein which was coursing in superior mediastinum anterior to the arch of aorta [Figure 1] and [Figure 2]. The accessory hemiazygous vein was seen draining into the left brachiocephalic (innominate) vein [Figure 2] and [Figure 3]. There was no communication between hemiazygous and azygous venous system which were draining separately. Right-sided azygous vein was normal in course draining into superior vena cava (SVC). MIP and volume rendering images (VRT) [Figure 4] demonstrated excellent anatomical details of these anatomical features.

Figure 1: Axial contrast-enhanced computed tomography thorax image shows continuation of left hemiazygous and accessory hemiazygous vein as shown by upper and lower arrows, respectively

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Figure 2: Axial contrast-enhanced computed tomography thorax image shows drainage of left accessory hemiazygous vein (lower arrow) into left brachiocephalic vein (upper arrow)

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Figure 3: Coronal maximum intensity projection image shows drainage of left accessory hemiazygous vein into left brachiocephalic vein (shown by arrow)

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Figure 4: Sagittal volume rendering technique image shows drainage of left accessory hemiazygous vein (horizontal arrow) into left brachiocephalic vein (vertical arrow)

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Discussion

Azygous venous system is thoracic continuations of the ascending lumbar veins and provides venous drainage for the intercostal and paravertebral veins within the posterior aspect of the thorax. The azygos vein drains into the posterior aspect of the SVC approximately 1 cm below the junction of the left and right innominate (brachiocephalic) veins.

Several variations in the branching pattern of the azygos vein have been reported. These abnormalities are generally explained by embryological development. Azygos vein originates embryologically from the subcardinal veins. The right subcardinal vein forms the azygos vein and the left subcardinal vein the hemiazygos vein.^[5]

At approximately T8–T9 vertebral level, the hemiazygos vein joins the azygos vein usually posterior to the aorta. The accessory hemiazygos joins the azygos at T7–T8 vertebral level crossing posterior to the aorta.^[6]

Rarely, a direct communication can be noted between the hemiazygous and the accessory hemiazygous veins as seen in 3.6% cases. These two veins have variable drainage and anatomy. When the hemiazygous and the accessory hemiazygous veins form common channels ventral to the aorta, it is called interazygous vein.^[7]

The accessory hemiazygos vein or superior hemiazygos vein is a left thoracic vein which normally drains predominantly the left posterior thoracic cage.^[8] 1–2% of the cases are seen to show that the accessory hemiazygos vein drains into the brachiocephalic vein.^[9]

The azygos system is an important collateral pathway in obstruction of superior and inferior vena cava. Prior knowledge of normal anatomical variation can avoid any misdiagnosis when these accessory venous pathways are also enlarged.

Knowledge of the aberrant venous anatomy is also important in surgery and catheter placement. Rarely, the hemiazygos system has also been mistaken for abnormal lymph nodes.

Conclusion

The documentation of the variations of the hemiazygous venous system is important even if it is noted incidentally. This should not be confused with other conditions like lymph nodes, aneurysms or small tumors.^[6] It is also important for the surgeon when operating any mediastinal pathology.

Contrast CT helps in accurate delineation of the anatomical venous pathway and its variants. Radiologist should be aware of these normal variations and should mention it in the reporting.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

References

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