A giant venous varix of the azygos arch is a very rare cause of a mediastinal mass. The usual diagnosis of a mediastinal mass by mediastinoscopy or percutaneous fine-needle aspiration or biopsy is very hazardous if there is a venous varix. Noninvasive thoracic CT scanning is a safe and better choice for diagnosis. We describe the case of a woman with a posterior mediastinal mass caused by a giant azygos vein varix. Thoracic CT documented the diagnosis. The etiology of the azygos varix was portal hypertension secondary to liver cirrhosis.
Key words: azygos vein varix; liver cirrhosis; mediastinal mass; portal hypertension
Abbreviation: HU = Hounsfield unit
The main causes of a dilated azygos vein include portal vein hypertension, obstruction of the superior vena cava, hypertension in the right-heart chamber, Budd-Chiari syndrome, hypervascular tumor draining into the azygos system, posttraumatic pseudoaneurysm, kinking of the aorta, and pregnancy. In some cases, no definitive cause is found. We report a case of azygos vein varix mimicking a mediastinal mass in a patient with liver cirrhosis.
A 61-year-old nonsmoking housewife was admitted to our hospital in 1999 with chest tightness of 1 month in duration. The discomfort was intermittent, radiated to her back, and was not aggravated by work. There was no cough, fever, hemoptysis, dyspnea on exertion, or pedal edema. She also denied a recent history of thoracic trauma. She had no known history of liver disease, nor did she drink alcoholic beverages. She was blind in both eyes following trauma at age 11 years. On examination, her BP was 136/79 mm Hg, heart rate was 80 beats/rain and regular, and the respiration rate was 18 breaths/rain with unlabored breathing. The chest, heart, and abdominal examinations were unremarkable. The ECG revealed sinus rhythm without ST-segment changes. Her hematocrit and hemoglobin were within the normal range. Her renal function was also within normal limits.
Her aspartate aminotransferase level of 41 U/L and alanine aminotransferase level of 31 U/L were slightly abnormal. Her albumin level was 3.9 g/dL, and total bilirubin level was 0.4 mg/dL. An abdominal echo revealed a liver with heterogenous echotexture and blunt margins, suggestive of chronic liver disease. Her hepatitis B surface antigen and anti-hepatitis C antibody were negative.
She was found to have a mediastinal mass on a supine anteroposterior chest radiograph. The lateral view showed a posterior mediastinal mass (Fig 1). A thoracic CT scan before and after IV contrast enhancement confirmed the presence of an enhancing mass located in the posterior mediastinum (Fig 2). This was interpreted as a neurogenic tumor or extramedullary hematopoiesis. Percutaneous biopsy was suggested, but the patient refused.
[FIGURES 1-2 OMITTED]
The chest tightness subsided spontaneously during hospitalization. On a second chest radiograph obtained with the patient standing, the mass had become nearly invisible (Fig 3). She was discharged and followed up closely.
[FIGURE 3 OMITTED]
She remained well until 2 years later, when she presented with hematemesis with abdominal fullness. Her aspartate aminotransferase level was 42 U/L, alanine aminotransferase level was 38 U/L, serum albumin level was 2.9g/dL, direct bilirubin level was 0.4 g/dL, and total bilirubin level was 1.1 g/dL. An abdominal ultrasound revealed liver cirrhosis along with splenomegaly and ascites. Gastroesophagoscopy revealed esophageal varices with active bleeding. The ascitic albumin level was 1.4 g/dL, giving a serum-ascites albumin gradient of 1.5. The diagnosis was liver cirrhosis with portal hypertension, esophageal variceal bleeding, and uncomplicated ascites.
A supine anteroposterior chest radiograph alter endotracheal intubation again showed a mediastinal mass. This time, the posterior mediastinal enhancing mass was located in the pathway of the azygos arch by thoracic CT scan. The mean CT number of the mass was 30 Hounsfield units (HU) [before contrast] and 100 HU (after contrast), indicating the mass was vascular in origin (Fig 4). A reconstructive two-dimensional image was made by spiral thoracic CT to prove the anatomic relationship between the mass and neighboring blood vessels (Fig 5). It was interpreted as vascular dilation compatible with a huge varix of the azygos vein.
[FIGURES 4-5 OMITTED]
After remission of this episode, the patient had recurrent esophageal bleeding. One year later, she died because of hepatic failure with refractory hematemesis during the last hospitalization.
Azygos vein varix is a rare cause of mediastinal mass. (1) Most posterior mediastinal masses are solid, such as neurogenic tumors, schwannoma, neurofibroma, ganglioneuroma, or may be cysts, such as forget cysts and pericardial cysts. (2) However, if we forget to include vascular causes of a mass, it is easy to misdiagnose a patient such as ours.
In our patient, the azygos vein dilation was probably caused by portal hypertension due to intrahepatic block secondary to liver cirrhosis. The portal, esophageal, and azygos veins play the major roles in venous drainage via the portosystemic collateral circulation in portal hypertension. The azygos vein connects with the portal system through the cervical esophageal vein, which then merges with various groups of veins from the lower esophagus, stomach, small intestine, spleen, large intestine, and rectum to form the portal vein at the hilum of the liver. In a patient with portal hypertension, the portal blood flows back into the splenic vein, spleen, gastroesophageal veins, and intrinsic esophageal veins, any of which may become varicose and drain upward through the thoracic and esophageal veins, thence into the azygos system and the systemic veins.
A CT scan readily demonstrates the anatomy of the azygos vein and can delineate the vascular characteristics of a dilated azygos vein. Generally, the azygos vein ascends in the posterior mediastinum on the right anterior aspect of the vertebral bodies. It arches forward over the right mainstem bronchus to drain into the superior vena cava at the level of the fourth thoracic vertebra. This is why an azygos vein varix mimics a posterior mediastinal mass. (3)
The change in the size of the mass between the supine and upright position on chest radiograph is a helpful clue that the mass is vascular. Recognizing this presentation may help to avoid a potentially dangerous attempt at diagnosis either by fine-needle aspiration or mediastinoscopic biopsy.
Azygos vein varix may be important in preventing variceal bleeding in patients with liver cirrhosis. It is known that the size and pressure of esophageal varices, which correlate with risk of hemorrhage, parallel azygos blood flow. (4) The volume of a compliant vessel increases more easily, according to the formula of elastic pressure: C = [DELTA]V/[DELTA]P, where C = compliance, [DELTA]V = volume change, and [DELTA]p = pressure change. According to the Hagen-Poisseulle equation in hydrokinetics (Q = [DELTA]p [pi]r (4)/8 [micro]L, where Q = flow velocity, r = the radius of a tube, [DELTA]p = the pressure gradient within the tube, and L = the length of the tube), when there is constant pressure in the portoesophageoazygos venous system, an increase in the cross-sectional area contributed by the azygos vein dilation decreases flow within the system. This in turn reduces the risk of variceal bleeding.
In addition to reducing the flow in the system overall, another factor may also be significant in preventing bleeding. In general, portal flow varies diurnally, with peak flow occurring at midnight. (4) The azygos varix increases in size when the patient is recumbent, further reducing flow in the system. This phenomenon, as with the administration of propranolol at night, may play an important role in preventing varietal bleeding. The azygos varix thus may be present on chest radiograph before varices are diagnosed. In our patient, the mediastinal mass was seen 2 years before her first episode of variceal bleeding.
In summary, a mediastinal mass in a patient with cirrhosis of the liver may be a giant azygos vein varix. An awareness of this possible diagnosis should perform noninvasive imaging procedures prior to invasive tests. A comparison between supine and standing chest radiographs is useful in differential diagnosis. However, a chest CT if necessary max be adequate to make the diagnosis.
ACKNOWLEDGMENT: We thank Dr. Mary Jeanne Buttrey, Consulting Physician, Department of Internal Medicine, Mackay Memorial Hospital, for review and revision of the manuscript.
* From the Chest Division (Drs. Lee, Kuo, Peng, F-J Lin, and C-C Lin), Gastroenterology Division (Dr. Shih), and Radiology Division (Dr. Sheu), Department of Internal Medicine, Mackay Memorial Hospital, Taipei, Taiwan, ROC.
(1) Miguel G, Rosa MM, Albert M, et al. Idiopathic azygos vein aneurysm: a rare cause of mediastinal mass, Thorax 1999; 54:653-655
(2) Strollo DC, Rosado-de-Christenson ML, Jett JR. Primary mediastinal tumors: part II: Tumors of the middle and posterior mediastinum. Chest 1997; 112:1344-1357
(3) Dunn V, Miller FJ Jr. Mediastinal mass in a patient with liver disease. JAMA 1982; 247:1873-1874
(4) Shigeo S, Kunihiro Y, Kayoko T, et al. Daily variation of azygos and ported blood flow and the effect of propranolol administration once evening in cirrhotics. J Hepatol 2001; 34:26-31
Manuscript received January 15, 2004; revision accepted August 24, 2004.
Reproduction of this article is prohibited without written permission from the American College of Chest Physicians e-mail: firstname.lastname@example.org).
Correspondence to: Hsu Tah Kuo, MBBS, FCCP, Department of Internal Medicine, Mackay Memorial Hospital, 92 Sec 2, Chung-Shan North Rd, Taipei, Taiwan, ROC; e-mail: Kuohsu@ms2. mmh.org.tw
COPYRIGHT 2005 American College of Chest Physicians
COPYRIGHT 2005 Gale Group