**2.5 Retro-aortic left renal vein**

As with circum-aortic left renal vein, a retro-aortic left renal vein results from persistence of the dorsal arch of the renal collar. However, in this variation the ventral arch (intersubcardinal anastomosis) regresses so that a single renal vein passes posterior to the aorta (Fig 6). The prevalence is 2.1%(i). The clinical significance is preoperative recognition of the anomaly.

Fig. 6. Retroaortic left renal vein in a 27-year-old man. (a) Schematic shows a single left renal vein, which crosses posterior to the aorta. (b, c) CT scans show the left renal vein (arrow) descending to cross posterior to the aorta.

Vena Cava Malformations as an

**IVC** 

**IVCA** 

Emerging Etiologic Factor for Deep Vein Thrombosis in Young Patients 53

**2.6 Double IVC with retro-aortic right renal vein and hemi-azygos continuation of the** 

More than one anomaly can coexist in a patient. In the case of a double IVC with a retro-aortic right renal vein and hemi-azygos continuation of the IVC, the embryologic basis is persistence of the left lumbar and thoracic supra-cardinal vein and the left supra-sub-cardinal anastomosis, together with failure of formation of the right sub-cardinal–hepatic anastomosis. In addition, the right renal vein and right IVC meet and cross posterior to the aorta to join the left IVC and continue cephalad as the hemi-azygos vein (Fig 7). Thus, there is also persistence of the dorsal limb of the renal collar and regression of the ventral limb. In the thorax, the hemiazygos vein crosses posterior to the aorta at approximately T8 or T9 to join the rudimentary azygos vein. Alternate collateral pathways for the hemi-azygos vein include cephalad continuation to join the coronary vein of the heart via a persistent left superior vena cava and

**2.7 Double IVC with retro-aortic left renal vein and hemiazygos continuation of the** 

Double IVC with a retro-aortic left renal vein and azygos continuation of the IVC is an interesting combination. It results from persistence of the left supracardinal vein and the dorsal limb of the renal collar with regression of the ventral limb. In addition, the subcardinal-hepatic anastomosis fails to form (Fig 7). A recent study demonstrated that azygos continuation of the IVC can be predicted with ultrasonography by identifying the right renal

A circum-caval ureter is also termed a retro-caval ureter. The right supra-cardinal system fails to develop, whereas the right posterior cardinal vein persists. The anomaly always occurs on the right side. The proximal ureter courses posterior to the IVC, then emerges to the right of the aorta, coming to lie anterior to the right iliac vessels (Fig 8). Patients with this anomaly may develop partial right ureteral obstruction or recurrent urinary tract infections.

Several reports have described absence of the entire IVC (o–r) or absence of the infra-renal IVC with preservation of the supra-renal segment (Fig 9) (s,t). Absence of the entire posthepatic IVC suggests that all three paired venous systems failed to develop properly. Absence of the infrarenal IVC implies failure of development of the posterior cardinal and supracardinal veins. Since it is difficult to identify a single embryonic event that can lead to either of these scenarios, there is controversy as to whether these conditions are true

The therapy of acute DVT in this kind of patients is similar of the currently recommended strategies and includes un-fractioned heparin, low-molecular weight heparin, fondaparinux

Therapeutic options include surgical relocation of the ureter anterior to the cava(i).

**2.9 Absent Infra-renal IVC with preservation of the supra-renal segment** 

**3. Implications for treatment of DVT and prevention of recurrences** 

embryonic anomalies or the result of perinatal IVC thrombosis (p,s,t).

an accessory hemi-azygos continuation to the left brachio-cephalic vein(n).

artery crossing abnormally anterior to the IVC (15).

**2.8 Circum-caval ureter** 

Fig. 7. Spinal dysraphism and double IVC with hemiazygos continuation in a 2-year-old boy. (a) Schematic shows failed development of the right pre-renal IVC and hemi-azygos continuation of the left IVC. (b-e) MR images presented from caudal to cranial show the anomaly. (b) Note the right (straight arrow) and left (curved arrow) IVCs. (c) The right renal vein (arrowhead) descends to receive the right IVC and crosses posterior to the aorta (arrow) to join the left IVC. (d) The left IVC continues cephalad left of the aorta under the diaphragmatic crus as the hemi-azygos vein (arrow). (e) In the thorax, the hemi-azygos vein (straight arrow) crosses posterior to the aorta (arrowhead) to join a rudimentary azygos vein (curved arrow) approximately 1-2 cm below the carina.

#### **2.6 Double IVC with retro-aortic right renal vein and hemi-azygos continuation of the IVC**

More than one anomaly can coexist in a patient. In the case of a double IVC with a retro-aortic right renal vein and hemi-azygos continuation of the IVC, the embryologic basis is persistence of the left lumbar and thoracic supra-cardinal vein and the left supra-sub-cardinal anastomosis, together with failure of formation of the right sub-cardinal–hepatic anastomosis. In addition, the right renal vein and right IVC meet and cross posterior to the aorta to join the left IVC and continue cephalad as the hemi-azygos vein (Fig 7). Thus, there is also persistence of the dorsal limb of the renal collar and regression of the ventral limb. In the thorax, the hemiazygos vein crosses posterior to the aorta at approximately T8 or T9 to join the rudimentary azygos vein. Alternate collateral pathways for the hemi-azygos vein include cephalad continuation to join the coronary vein of the heart via a persistent left superior vena cava and an accessory hemi-azygos continuation to the left brachio-cephalic vein(n).

#### **2.7 Double IVC with retro-aortic left renal vein and hemiazygos continuation of the IVCA**

Double IVC with a retro-aortic left renal vein and azygos continuation of the IVC is an interesting combination. It results from persistence of the left supracardinal vein and the dorsal limb of the renal collar with regression of the ventral limb. In addition, the subcardinal-hepatic anastomosis fails to form (Fig 7). A recent study demonstrated that azygos continuation of the IVC can be predicted with ultrasonography by identifying the right renal artery crossing abnormally anterior to the IVC (15).

#### **2.8 Circum-caval ureter**

52 Deep Vein Thrombosis

(a)

Fig. 7. Spinal dysraphism and double IVC with hemiazygos continuation in a 2-year-old boy. (a) Schematic shows failed development of the right pre-renal IVC and hemi-azygos continuation of the left IVC. (b-e) MR images presented from caudal to cranial show the anomaly. (b) Note the right (straight arrow) and left (curved arrow) IVCs. (c) The right renal vein (arrowhead) descends to receive the right IVC and crosses posterior to the aorta (arrow) to join the left IVC. (d) The left IVC continues cephalad left of the aorta under the diaphragmatic crus as the hemi-azygos vein (arrow). (e) In the thorax, the hemi-azygos vein (straight arrow) crosses posterior to the aorta (arrowhead) to join a rudimentary azygos vein

(curved arrow) approximately 1-2 cm below the carina.

A circum-caval ureter is also termed a retro-caval ureter. The right supra-cardinal system fails to develop, whereas the right posterior cardinal vein persists. The anomaly always occurs on the right side. The proximal ureter courses posterior to the IVC, then emerges to the right of the aorta, coming to lie anterior to the right iliac vessels (Fig 8). Patients with this anomaly may develop partial right ureteral obstruction or recurrent urinary tract infections. Therapeutic options include surgical relocation of the ureter anterior to the cava(i).

#### **2.9 Absent Infra-renal IVC with preservation of the supra-renal segment**

Several reports have described absence of the entire IVC (o–r) or absence of the infra-renal IVC with preservation of the supra-renal segment (Fig 9) (s,t). Absence of the entire posthepatic IVC suggests that all three paired venous systems failed to develop properly.

Absence of the infrarenal IVC implies failure of development of the posterior cardinal and supracardinal veins. Since it is difficult to identify a single embryonic event that can lead to either of these scenarios, there is controversy as to whether these conditions are true embryonic anomalies or the result of perinatal IVC thrombosis (p,s,t).
