Abdominal Imaging
ª Springer Science+Business Media New York 2014 Published online: 1 July 2014
Abdom Imaging (2015) 40:159–166 DOI: 10.1007/s00261-014-0187-9
Multiplanar imaging of inferior vena cava variants Muhammad Awais,1 Abdul Rehman,2 Noor Ul-Ain Baloch,2 Basit Salam1 1 2
Department of Radiology, Aga Khan University Hospital, Karachi, Sindh, Pakistan Department of Biological & Biomedical Sciences, Aga Khan University, Karachi, Sindh, Pakistan
Abstract Inferior vena cava (IVC) variants are rare and are usually detected incidentally. Even though, these variants are by themselves asymptomatic, they can have important clinical, radiological, and surgical implications. In this pictorial essay, we sensitize the reader to various IVC variants by presenting reports of actual patients. A succinct description of the embryological development of these anatomic variants is also provided. Key words: Inferior vena cava—Inferior vena cava abnormalities—Inferior vena cava radiography—Inferior vena cava surgery
Anomalies of the inferior vena cava (IVC) are often asymptomatic and are diagnosed incidentally. The prevalence of various IVC anomalies has been reported to be 0.07–8.7% in the general population [1]. Albeit asymptomatic, these anomalies can lead to significant morbidity and mortality if not diagnosed properly [2]. Working knowledge of the normal developmental anatomy is crucial to understanding these abnormalities. This in turn has important implications in the management of patients with these variants and to prevent any potential catastrophe occurring intra-operatively. Newer imaging modalities like multi-detector CT (MDCT) with facilities of 3-dimensional reformatted coronal and sagittal imaging have allowed accurate visualization of these variants and thorough evaluation of any associated abnormalities. In this pictorial essay, we enumerate the diverse anatomical variants of the IVC that can occur, the embryological development which leads to the formation of these variants and their potential clinical repercussions if left undiagnosed. Emphasis has been placed on newer imaging modalities (like MDCT) that
Correspondence to: Muhammad Awais; email: [email protected]
have revolutionized the evaluation of these anatomical variants and their associated abnormalities.
Embryology In order to understand the complex developmental embryology of this important venous channel, it is helpful to divide the IVC into various segments on the basis of the primitive vessels that give rise to these segments. Table 1 summarizes these segments along with their relevant primitive vessels. It is important to recognize that each of these segments develops separately and perturbations in the development of these segments lead to the formation of complex IVC variants. IVC usually starts to develop in the sixth week of intrauterine life from three pairs of primitive venous channels that are formed serially. These venous conduits undergo sequential anastomosis and regression in order to form a composite venous channel [3]. The three pairs of precursor venous channels, in order of the timing of their appearance, are posterior cardinal veins, subcardinal veins, and supracardinal veins. All these venous channels are formed bilaterally and usually have appeared by the eighth week of intrauterine life. The first of the primitive vessels to appear are the posterior cardinal veins, which drain the caudal half of the fetus. Posterior cardinal veins themselves drain into the common cardinal veins, which also receive the anterior cardinal veins (draining the cranial half of the body). All these venous channels eventually drain into the sinus venosus. Two subcardinal veins develop shortly after the development of the posterior cardinal veins. These initially lie medial to the posterior cardinal veins, but, eventually replace the posterior cardinal veins for the venous drainage of the lower half of the body. The posterior cardinal veins gradually regress in their cranial most parts and only their caudal most part is retained, where these are joined by the sacrocardinal veins to form the common iliac veins.
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Table 1. Classification of IVC variants on the basis of primitive venous channels Primitive vessels
Embryological derivatives
Anatomic variants
Posterior cardinal veins
Usually regress and do not form any major segment of the IVC
Subcardinal veins
Form the suprarenal portion of the IVC; their anastomosis with hepatic sinusoids lead to the formation of the hepatic portion of the IVC
Supracardinal veins
Form the infra-renal part of the IVC
Renal veins
Usually formed only from the ventral divisions; their dorsal portions regress bilaterally
Persistence of this channel leads to the formation of a more medially and posteriorly placed retro-caval ureter Failure to develop, or regression, of these vessels can lead to an interrupted IVC with or without azygous continuation If these vessels persist on the left side, they can lead to the formation of a left-sided supra-renal IVC Failure of these vessels to regress on the left side leads to the formation of a duplicated IVC If there is persistence of these vessels on the left side with regression on the right side, a left-sided IVC can occur If these vessels fail to develop or regress bilaterally, there may be an altogether absent infra-renal IVC Persistence of both the ventral and dorsal portions gives rise to a circum-aortic left renal vein If the dorsal segment persists instead of the ventral portion, it leads to the formation of a retro-aortic left renal vein
IVC, inferior vena cava
Simultaneous with the development of subcardinal veins, hepatic sinusoids also develop from the vitelline veins. These anastomose with each other and with the cranial aspect of the right subcardinal vein. This anastomosis between the developing hepatic sinusoids and the cranial most part of the right subcardinal vein forms the hepatic portion of the IVC. Just inferior to this, the remaining cranial portion of the right subcardinal vein forms the supra-renal portion of the IVC. The cranial most part of the left subcardinal vein persists as the left adrenal vein. Concurrent to the development of hepatic sinusoids is the development of the last pair of the primitive venous channels—supracardinal veins. Supracardinal veins gradually replace the caudal parts of the subcardinal vessels and overtake the venous drainage of the lower half of the body. The subcardinal veins, however, persist in their caudal most extremes forming the gonadal vessels. The supracardinal veins are not only responsible for forming the infra-renal portion of the IVC, but also for the formation of the renal veins, which form as a result of the anastomosis between the regressing subcardinal veins and the newly developed supracardinal veins. The so formed renal veins initially appear as a pair of dorsal and ventral renal veins on each side, but subsequently, the dorsal parts regress and only the ventral portions are retained as the renal veins. To recapitulate, the embryological development of IVC is a complex process involving the sequential formation, anastomosis and regression of three pairs of venous channels. Many classification systems have been devised for the categorization of IVC variants based on their embryological development [4]. One such system is given in Table 1. Understanding the development of the IVC is crucial for appreciating its various variants and their classification.
Fig. 1. A IVC lying on the left side of the aorta with a typical venous wave pattern noted on pulsed Doppler. B Arterial wave pattern of the aorta demonstrated to the right of the IVC.
Clinical implications Intra-operative catastrophe Non-recognition of IVC variants like retro-aortic or circum-aortic renal veins can lead to significant injury
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Fig. 2. A Normal position of the infra-hepatic portion (yellow arrow) of the IVC as seen on axial sections. B IVC crossing the midline just anterior to the aorta. C IVC lying to the left of
the aorta. D Reformatted coronal image demonstrating the IVC (yellow arrows) crossing to the left of the aorta (blue arrow).
to these vessels during intra-abdominal exploration. Often, these anomalous venous channels are very tortuous and dilated, making them even more prone to injury during surgery. Since IVC is a major venous
conduit draining almost all of the lower half of the body, potentially life-threatening hemorrhage can result from iatrogenic injury to this structure [5].
162
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Fig. 3. A Axial section demonstrating bilateral IVC (yellow arrows) on either side of the aorta. B Left-sided IVC crossing the midline anterior to the aorta to join the right-sided IVC. C
Coronal images re-demonstrate the duplicated IVC. D A common right-sided IVC passing through the liver to drain into the right atrium.
Studies published in the past have reported aortic dissection and aortic transection occurring in cases of unrecognized retro-aortic or circum-aortic IVC [6]. Furthermore, in these patients, it becomes extremely difficult to control bleeding from the injured aorta owing to poor control of the proximal aorta. In some instances, ureters have been misrecognized as vessels and subsequently injured during surgery [7]. Some literature sug-
gests that extensive manipulation during abdominal surgery in these patients can result in an increased incidence of post-operative pancreatitis and injury to the surrounding major branches of abdominal aorta [8]. Surgeons performing surgical procedures in such patients should always apply gentle traction on these vessels as extensive dissection of these structures is associated with an increased risk of complications.
163
M. Awais et al.: Multiplanar imaging of IVC variants
embolism and cerebrovascular accidents [9–11]. In patients with IVC duplication, two Greenfield filters are required for effective protection against thromboembolism; failing to recognize this variant may result in embolic events even after the placement of a single IVC filter. Likewise, patients who continue to experience embolic events following the placement of an IVC filter may have an undiagnosed IVC duplication [12]. There are few instances in which thrombosed IVC variants have been misdiagnosed as retroperitoneal tumors [13]. In one case, the azygous continuation of the IVC was misdiagnosed as dissection of the aorta and a mediastinal mass lesion [14]. These cases show that it is imperative for all radiologists and surgeons to recognize these anatomic variants to avoid wrong diagnoses and intra-operative catastrophes.
Tumor staging Extension of renal cell carcinoma and other malignant neoplasms into IVC variants can be missed easily. This can lead to erroneous tumor staging with subsequent inappropriate management and potentially grave outcomes for the patient [15]. Variations may also exist in the lymphatic drainage along these venous variants, which may require extensive lymph node dissection during surgery for pelvic tumors [16, 17]. Therefore, the possibility of neoplastic extension in to these variants and any associated variations in the lymphatic drainage should be thoroughly considered and accurately evaluated in such patients.
Common variants In this section, we present an account of various cases, seen at our institution, of IVC anomalies.
Left-sided IVC
Fig. 4. A Duplication of IVC noted on an axial section (yellow arrows). B The left-sided IVC passing posterior to the aorta to drain into the right-sided IVC. C Absence of the intrahepatic portion of the IVC along with a prominent azygous vein (blue arrow) just to the right of the aorta behind the right crus of diaphragm.
Thromboembolic complications A thrombus in an anatomical variant may undergo unrecognized and can subsequently lead to pulmonary
A 34-year-old male presented with mild pain in the right hypochondrium. Baseline laboratory investigations revealed a raised alanine aminotransferase level. Ultrasonography of the liver was performed, which revealed a left-sided IVC (Fig. 1), but, it was otherwise unremarkable. Further laboratory work-up revealed that the patient had hepatitis B virus (HBV) and hepatitis E virus (HEV) co-infection as evidenced by positive HBV DNA and positive HEV antibodies. The finding of left-sided IVC in this patient was incidental and it was picked up on ultrasonography. Another patient, a 53-year-old male with known hepatocellular carcinoma, had undergone transarterial chemoembolization of hepatoma at our institution. A follow-up CT scan was performed, which was the first scan of this patient at our institution. Again, there was an incidental finding of left-sided IVC, accurately iden-
164
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Fig. 5. A IVC identified to the left of the aorta (yellow arrow) on this axial section; associated findings include midline liver, multiple spleens, and right-sided stomach. B Absence of the left-sided IVC on this section suggests interruption of the IVC; a prominent azygous vein, just to the left of the aorta, repre-
sents an azygous continuation. C Coronal section re-demonstrating a left-sided IVC, which becomes attenuated just below the left hemi-diaphragm. D A prominent azygous vein, instead of the IVC, is located posterior to the aorta (pink arrow).
tified on multiplanar CT examination. The complete extent and relationship of this variant with other important structures could be easily appreciated on the multiplanar images (Fig. 2).
However, the patient did not have any evidence of pulmonary embolism or deep vein thrombosis.
Duplication of IVC A 50-year-old lady with a history of ovarian carcinoma suddenly developed shortness of breath. A CT scan was performed for the evaluation of possible pulmonary embolism and/or progression of disease. On this scan, an incidental finding of duplication of IVC was identified (Fig. 3). In this case, documentation of duplication of IVC was important as the patient may require two IVC filters for protection against pulmonary embolism.
Interrupted right-sided IVC with azygous continuation A 28-years-old man presented with complaints of periumbilical abdominal pain, which had now shifted to the right iliac fossa. Associated right iliac fossa tenderness and leukocytosis were noted on laboratory investigations. A CT scan was performed with the clinical suspicion of acute appendicitis. In this patient, an incidental finding of interrupted right-sided IVC with azygous continuation was noted (Fig. 4). The importance of documenting this finding pre-operatively in this case is
165
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Fig. 6. A A persistent dorsal left renal vein (blue arrow) noted on this axial section, in addition to the normal (ventral) left renal vein (yellow arrow); the ventral left renal vein passes anterior to the aorta to drain into the IVC. B The dorsal left
renal vein passing posteriorly to the aorta to drain into the IVC. C Sagittal images demonstrating a circum-aortic collar (pink arrow) formed by the ventral and dorsal left renal veins.
that the interrupted right-sided IVC might be confused with post-operative collection or lymphadenopathy on subsequent scans.
plain radiograph of the right knee joint was obtained followed by an MRI. Based on the radiographic appearances, there was a strong suspicion of giant cell tumor. Patient then underwent a CT examination as part of staging work-up, which revealed multiple enlarged para-aortic lymph nodes and lung metastases. There was also an incidental finding of circum-aortic left renal vein in this patient (Fig. 6). Again, this important finding if left undiagnosed could lead to significant morbidity during any subsequent abdominal surgery.
Interrupted left-sided IVC with azygous continuation A 15-years-old boy was brought for the evaluation of complex congenital heart disease. Trans-thoracic echocardiography was performed, which revealed situs inversus with levocardia and an unbalanced complete atrioventricular septal defect. A single ventricle of right ventricular morphology was identified with double outflow tract and a large patent ductus arteriosus. CT angiography was requested for delineation of the complex anatomy, which revealed an interrupted left-sided IVC with azygous vein continuation on the left side (Fig. 5). In this patient, accurate delineation of anatomy was necessary for subsequent planning of surgical management.
Circum-aortic left renal vein A 24-years-old lady presented with complaints of pain and swelling in the right knee for the past 6 months. A
Retrocaval ureter A 60-year-old woman presented with lower urinary tract symptoms. An intravenous pyelogram was obtained to detect any possible renal abnormalities. On this examination, kinking of the right ureter was noted at the level of the lower pole of the right kidney along with proximal hydroureter and hydronephrosis. The lower mid-portion of the ureter seemed more medial than usual suggestive of a retro-caval position of the ureter along with mild proximal obstruction.
166
Conclusion Understanding the embryological development of the IVC is crucial to appreciate its various anatomic variants. It is imperative for all radiologists and surgeons to be able to recognize these anatomic variants as an inability to do so can result in potentially lethal intraoperative catastrophes. Conflict of interests The authors of this manuscript declare no conflict of interests regarding the findings reported herein.
References 1. Obernosterer A, Aschauer M, Schnedl W, Lipp RW (2002) Anomalies of the inferior vena cava in patients with iliac venous thrombosis. Ann Intern Med 136:37–41. doi:10.7326/0003-4819136-1-200201010-00009 2. Malaki M, Willis AP, Jones RG (2012) Congenital anomalies of the inferior vena cava. Clin Radiol 67:165–171. doi:10.1016/j.crad. 2011.08.006 3. Cheng YF, Huang TL, Chen CL, et al. (1997) Variations of the middle and inferior right hepatic vein: application in hepatectomy. J Clin Ultrasound 25:175–182. doi:10.1002/(SICI)1097-0096 (199705)25:43.0.CO;2-B 4. Chuang VP, Mena CE, Hoskins PA (1974) Congenital anomalies of the inferior vena cava. Review of embryogenesis and presentation of a simplified classification. Br J Radiol 47:206–213. doi:10.1259/ 0007-1285-47-556-206 5. Stefan´czyk L, Majos M, Majos A, Polguj M (2014) Duplication of the inferior vena cava and retroaortic left renal vein in a patient with large abdominal aortic aneurysm. Vasc Med 19:144–145. doi: 10.1177/1358863X14521891 6. Bartle EJ, Pearce WH, Sun JH, Rutherford RB (1987) Infrarenal venous anomalies and aortic surgery: avoiding vascular injury. J Vasc Surg 6:590–593. doi:10.1016/0741-5214(87)90276-X
M. Awais et al.: Multiplanar imaging of IVC variants
7. Raju S, Hollis K, Neglen P (2006) Obstructive lesions of the inferior vena cava: clinical features and endovenous treatment. J Vasc Surg 44:820–827. doi:10.1016/j.jvs.2006.05.054 8. Sarma KP (1966) Anomalous inferior vena cava-anatomical and clinical. Br J Surg 53:600–602. doi:10.1002/bjs.1800530710 9. Shingleton WB, Hutton M, Resnick MI (1994) Duplication of inferior vena cava: its importance in retroperitoneal surgery. Urology 43:113–115. doi:10.1016/S0090-4295(94)80281-5 10. Sarlon G, Bartolli MA, Muller C, et al. (2011) Congenital anomalies of inferior vena cava in young patients with iliac deep venous thrombosis. Ann Vasc Surg 25:265.e5–265.e8. doi:10.1016/j.avsg. 2010.07.007 11. Skeik N, Wickstrom KK, Schumacher CW, Sullivan TM (2013) Infrahepatic inferior vena cava agenesis with bilateral renal vein thrombosis. Ann Vasc Surg 27:973.e19–973.e23. doi:10.1016/j.avsg. 2012.10.030 12. Malgor RD, Oropallo A, Wood E, Natan K, Labropoulos N (2011) Filter placement for duplicated cava. Vasc Endovasc Surg 45:269–273. doi:10.1177/1538574410395041 13. Arisawa C, Kihara K, Fujii Y, et al. (1999) Possible misinterpretation on computed tomography of left inferior vena cava as retroperitoneal lymph node metastasis: a report of two cases. Int J Urol 6:215–218. doi:10.1046/j.1442-2042.1999.06445.x 14. Evans AJ (1993) Azygos/accessory hemiazygos continuation of inferior vena cava mimicking dissection of the aorta. Clin Radiol 48:207–209. doi:10.1016/S0009-9260(05)80285-5 15. Lee EK, Wetzel LH, Holzbeierlein JM (2011) Circumaortic renal vein tumor thrombus in renal cell carcinoma. Int J Urol 18:605– 606. doi:10.1111/j.1442-2042.2011.02790.x 16. Castillo OA, Sanchez-Salas R, Alvarez JM, Vitagliano G, Cortes O (2008) Inferior vena cava anomalies during laparoscopic retroperitoneal lymph node dissection. J Endourol 22:327–332. doi: 10.1089/end.2007.0112 17. Strauss A, Kuemper C, Mundhenke C, et al. (2011) Congenital retroperitoneal vascular anomalies: impact on pelvic surgery. Arch Gynecol Obstet 284:1169–1173. doi:10.1007/s00404-010-1803-8
ª Springer Science+Business Media New York 2014 Published online: 1 July 2014
Abdom Imaging (2015) 40:159–166 DOI: 10.1007/s00261-014-0187-9
Multiplanar imaging of inferior vena cava variants Muhammad Awais,1 Abdul Rehman,2 Noor Ul-Ain Baloch,2 Basit Salam1 1 2
Department of Radiology, Aga Khan University Hospital, Karachi, Sindh, Pakistan Department of Biological & Biomedical Sciences, Aga Khan University, Karachi, Sindh, Pakistan
Abstract Inferior vena cava (IVC) variants are rare and are usually detected incidentally. Even though, these variants are by themselves asymptomatic, they can have important clinical, radiological, and surgical implications. In this pictorial essay, we sensitize the reader to various IVC variants by presenting reports of actual patients. A succinct description of the embryological development of these anatomic variants is also provided. Key words: Inferior vena cava—Inferior vena cava abnormalities—Inferior vena cava radiography—Inferior vena cava surgery
Anomalies of the inferior vena cava (IVC) are often asymptomatic and are diagnosed incidentally. The prevalence of various IVC anomalies has been reported to be 0.07–8.7% in the general population [1]. Albeit asymptomatic, these anomalies can lead to significant morbidity and mortality if not diagnosed properly [2]. Working knowledge of the normal developmental anatomy is crucial to understanding these abnormalities. This in turn has important implications in the management of patients with these variants and to prevent any potential catastrophe occurring intra-operatively. Newer imaging modalities like multi-detector CT (MDCT) with facilities of 3-dimensional reformatted coronal and sagittal imaging have allowed accurate visualization of these variants and thorough evaluation of any associated abnormalities. In this pictorial essay, we enumerate the diverse anatomical variants of the IVC that can occur, the embryological development which leads to the formation of these variants and their potential clinical repercussions if left undiagnosed. Emphasis has been placed on newer imaging modalities (like MDCT) that
Correspondence to: Muhammad Awais; email: [email protected]
have revolutionized the evaluation of these anatomical variants and their associated abnormalities.
Embryology In order to understand the complex developmental embryology of this important venous channel, it is helpful to divide the IVC into various segments on the basis of the primitive vessels that give rise to these segments. Table 1 summarizes these segments along with their relevant primitive vessels. It is important to recognize that each of these segments develops separately and perturbations in the development of these segments lead to the formation of complex IVC variants. IVC usually starts to develop in the sixth week of intrauterine life from three pairs of primitive venous channels that are formed serially. These venous conduits undergo sequential anastomosis and regression in order to form a composite venous channel [3]. The three pairs of precursor venous channels, in order of the timing of their appearance, are posterior cardinal veins, subcardinal veins, and supracardinal veins. All these venous channels are formed bilaterally and usually have appeared by the eighth week of intrauterine life. The first of the primitive vessels to appear are the posterior cardinal veins, which drain the caudal half of the fetus. Posterior cardinal veins themselves drain into the common cardinal veins, which also receive the anterior cardinal veins (draining the cranial half of the body). All these venous channels eventually drain into the sinus venosus. Two subcardinal veins develop shortly after the development of the posterior cardinal veins. These initially lie medial to the posterior cardinal veins, but, eventually replace the posterior cardinal veins for the venous drainage of the lower half of the body. The posterior cardinal veins gradually regress in their cranial most parts and only their caudal most part is retained, where these are joined by the sacrocardinal veins to form the common iliac veins.
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Table 1. Classification of IVC variants on the basis of primitive venous channels Primitive vessels
Embryological derivatives
Anatomic variants
Posterior cardinal veins
Usually regress and do not form any major segment of the IVC
Subcardinal veins
Form the suprarenal portion of the IVC; their anastomosis with hepatic sinusoids lead to the formation of the hepatic portion of the IVC
Supracardinal veins
Form the infra-renal part of the IVC
Renal veins
Usually formed only from the ventral divisions; their dorsal portions regress bilaterally
Persistence of this channel leads to the formation of a more medially and posteriorly placed retro-caval ureter Failure to develop, or regression, of these vessels can lead to an interrupted IVC with or without azygous continuation If these vessels persist on the left side, they can lead to the formation of a left-sided supra-renal IVC Failure of these vessels to regress on the left side leads to the formation of a duplicated IVC If there is persistence of these vessels on the left side with regression on the right side, a left-sided IVC can occur If these vessels fail to develop or regress bilaterally, there may be an altogether absent infra-renal IVC Persistence of both the ventral and dorsal portions gives rise to a circum-aortic left renal vein If the dorsal segment persists instead of the ventral portion, it leads to the formation of a retro-aortic left renal vein
IVC, inferior vena cava
Simultaneous with the development of subcardinal veins, hepatic sinusoids also develop from the vitelline veins. These anastomose with each other and with the cranial aspect of the right subcardinal vein. This anastomosis between the developing hepatic sinusoids and the cranial most part of the right subcardinal vein forms the hepatic portion of the IVC. Just inferior to this, the remaining cranial portion of the right subcardinal vein forms the supra-renal portion of the IVC. The cranial most part of the left subcardinal vein persists as the left adrenal vein. Concurrent to the development of hepatic sinusoids is the development of the last pair of the primitive venous channels—supracardinal veins. Supracardinal veins gradually replace the caudal parts of the subcardinal vessels and overtake the venous drainage of the lower half of the body. The subcardinal veins, however, persist in their caudal most extremes forming the gonadal vessels. The supracardinal veins are not only responsible for forming the infra-renal portion of the IVC, but also for the formation of the renal veins, which form as a result of the anastomosis between the regressing subcardinal veins and the newly developed supracardinal veins. The so formed renal veins initially appear as a pair of dorsal and ventral renal veins on each side, but subsequently, the dorsal parts regress and only the ventral portions are retained as the renal veins. To recapitulate, the embryological development of IVC is a complex process involving the sequential formation, anastomosis and regression of three pairs of venous channels. Many classification systems have been devised for the categorization of IVC variants based on their embryological development [4]. One such system is given in Table 1. Understanding the development of the IVC is crucial for appreciating its various variants and their classification.
Fig. 1. A IVC lying on the left side of the aorta with a typical venous wave pattern noted on pulsed Doppler. B Arterial wave pattern of the aorta demonstrated to the right of the IVC.
Clinical implications Intra-operative catastrophe Non-recognition of IVC variants like retro-aortic or circum-aortic renal veins can lead to significant injury
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161
Fig. 2. A Normal position of the infra-hepatic portion (yellow arrow) of the IVC as seen on axial sections. B IVC crossing the midline just anterior to the aorta. C IVC lying to the left of
the aorta. D Reformatted coronal image demonstrating the IVC (yellow arrows) crossing to the left of the aorta (blue arrow).
to these vessels during intra-abdominal exploration. Often, these anomalous venous channels are very tortuous and dilated, making them even more prone to injury during surgery. Since IVC is a major venous
conduit draining almost all of the lower half of the body, potentially life-threatening hemorrhage can result from iatrogenic injury to this structure [5].
162
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Fig. 3. A Axial section demonstrating bilateral IVC (yellow arrows) on either side of the aorta. B Left-sided IVC crossing the midline anterior to the aorta to join the right-sided IVC. C
Coronal images re-demonstrate the duplicated IVC. D A common right-sided IVC passing through the liver to drain into the right atrium.
Studies published in the past have reported aortic dissection and aortic transection occurring in cases of unrecognized retro-aortic or circum-aortic IVC [6]. Furthermore, in these patients, it becomes extremely difficult to control bleeding from the injured aorta owing to poor control of the proximal aorta. In some instances, ureters have been misrecognized as vessels and subsequently injured during surgery [7]. Some literature sug-
gests that extensive manipulation during abdominal surgery in these patients can result in an increased incidence of post-operative pancreatitis and injury to the surrounding major branches of abdominal aorta [8]. Surgeons performing surgical procedures in such patients should always apply gentle traction on these vessels as extensive dissection of these structures is associated with an increased risk of complications.
163
M. Awais et al.: Multiplanar imaging of IVC variants
embolism and cerebrovascular accidents [9–11]. In patients with IVC duplication, two Greenfield filters are required for effective protection against thromboembolism; failing to recognize this variant may result in embolic events even after the placement of a single IVC filter. Likewise, patients who continue to experience embolic events following the placement of an IVC filter may have an undiagnosed IVC duplication [12]. There are few instances in which thrombosed IVC variants have been misdiagnosed as retroperitoneal tumors [13]. In one case, the azygous continuation of the IVC was misdiagnosed as dissection of the aorta and a mediastinal mass lesion [14]. These cases show that it is imperative for all radiologists and surgeons to recognize these anatomic variants to avoid wrong diagnoses and intra-operative catastrophes.
Tumor staging Extension of renal cell carcinoma and other malignant neoplasms into IVC variants can be missed easily. This can lead to erroneous tumor staging with subsequent inappropriate management and potentially grave outcomes for the patient [15]. Variations may also exist in the lymphatic drainage along these venous variants, which may require extensive lymph node dissection during surgery for pelvic tumors [16, 17]. Therefore, the possibility of neoplastic extension in to these variants and any associated variations in the lymphatic drainage should be thoroughly considered and accurately evaluated in such patients.
Common variants In this section, we present an account of various cases, seen at our institution, of IVC anomalies.
Left-sided IVC
Fig. 4. A Duplication of IVC noted on an axial section (yellow arrows). B The left-sided IVC passing posterior to the aorta to drain into the right-sided IVC. C Absence of the intrahepatic portion of the IVC along with a prominent azygous vein (blue arrow) just to the right of the aorta behind the right crus of diaphragm.
Thromboembolic complications A thrombus in an anatomical variant may undergo unrecognized and can subsequently lead to pulmonary
A 34-year-old male presented with mild pain in the right hypochondrium. Baseline laboratory investigations revealed a raised alanine aminotransferase level. Ultrasonography of the liver was performed, which revealed a left-sided IVC (Fig. 1), but, it was otherwise unremarkable. Further laboratory work-up revealed that the patient had hepatitis B virus (HBV) and hepatitis E virus (HEV) co-infection as evidenced by positive HBV DNA and positive HEV antibodies. The finding of left-sided IVC in this patient was incidental and it was picked up on ultrasonography. Another patient, a 53-year-old male with known hepatocellular carcinoma, had undergone transarterial chemoembolization of hepatoma at our institution. A follow-up CT scan was performed, which was the first scan of this patient at our institution. Again, there was an incidental finding of left-sided IVC, accurately iden-
164
M. Awais et al.: Multiplanar imaging of IVC variants
Fig. 5. A IVC identified to the left of the aorta (yellow arrow) on this axial section; associated findings include midline liver, multiple spleens, and right-sided stomach. B Absence of the left-sided IVC on this section suggests interruption of the IVC; a prominent azygous vein, just to the left of the aorta, repre-
sents an azygous continuation. C Coronal section re-demonstrating a left-sided IVC, which becomes attenuated just below the left hemi-diaphragm. D A prominent azygous vein, instead of the IVC, is located posterior to the aorta (pink arrow).
tified on multiplanar CT examination. The complete extent and relationship of this variant with other important structures could be easily appreciated on the multiplanar images (Fig. 2).
However, the patient did not have any evidence of pulmonary embolism or deep vein thrombosis.
Duplication of IVC A 50-year-old lady with a history of ovarian carcinoma suddenly developed shortness of breath. A CT scan was performed for the evaluation of possible pulmonary embolism and/or progression of disease. On this scan, an incidental finding of duplication of IVC was identified (Fig. 3). In this case, documentation of duplication of IVC was important as the patient may require two IVC filters for protection against pulmonary embolism.
Interrupted right-sided IVC with azygous continuation A 28-years-old man presented with complaints of periumbilical abdominal pain, which had now shifted to the right iliac fossa. Associated right iliac fossa tenderness and leukocytosis were noted on laboratory investigations. A CT scan was performed with the clinical suspicion of acute appendicitis. In this patient, an incidental finding of interrupted right-sided IVC with azygous continuation was noted (Fig. 4). The importance of documenting this finding pre-operatively in this case is
165
M. Awais et al.: Multiplanar imaging of IVC variants
Fig. 6. A A persistent dorsal left renal vein (blue arrow) noted on this axial section, in addition to the normal (ventral) left renal vein (yellow arrow); the ventral left renal vein passes anterior to the aorta to drain into the IVC. B The dorsal left
renal vein passing posteriorly to the aorta to drain into the IVC. C Sagittal images demonstrating a circum-aortic collar (pink arrow) formed by the ventral and dorsal left renal veins.
that the interrupted right-sided IVC might be confused with post-operative collection or lymphadenopathy on subsequent scans.
plain radiograph of the right knee joint was obtained followed by an MRI. Based on the radiographic appearances, there was a strong suspicion of giant cell tumor. Patient then underwent a CT examination as part of staging work-up, which revealed multiple enlarged para-aortic lymph nodes and lung metastases. There was also an incidental finding of circum-aortic left renal vein in this patient (Fig. 6). Again, this important finding if left undiagnosed could lead to significant morbidity during any subsequent abdominal surgery.
Interrupted left-sided IVC with azygous continuation A 15-years-old boy was brought for the evaluation of complex congenital heart disease. Trans-thoracic echocardiography was performed, which revealed situs inversus with levocardia and an unbalanced complete atrioventricular septal defect. A single ventricle of right ventricular morphology was identified with double outflow tract and a large patent ductus arteriosus. CT angiography was requested for delineation of the complex anatomy, which revealed an interrupted left-sided IVC with azygous vein continuation on the left side (Fig. 5). In this patient, accurate delineation of anatomy was necessary for subsequent planning of surgical management.
Circum-aortic left renal vein A 24-years-old lady presented with complaints of pain and swelling in the right knee for the past 6 months. A
Retrocaval ureter A 60-year-old woman presented with lower urinary tract symptoms. An intravenous pyelogram was obtained to detect any possible renal abnormalities. On this examination, kinking of the right ureter was noted at the level of the lower pole of the right kidney along with proximal hydroureter and hydronephrosis. The lower mid-portion of the ureter seemed more medial than usual suggestive of a retro-caval position of the ureter along with mild proximal obstruction.
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Conclusion Understanding the embryological development of the IVC is crucial to appreciate its various anatomic variants. It is imperative for all radiologists and surgeons to be able to recognize these anatomic variants as an inability to do so can result in potentially lethal intraoperative catastrophes. Conflict of interests The authors of this manuscript declare no conflict of interests regarding the findings reported herein.
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