The Circle of Willis (CoW) is a ring-like network of blood vessels that perfuses the brain. Flow in the collateral pathways that connect major arterial inputs in the CoW change dynamically in response to vessel narrowing or occlusion. Vasospasm is an involuntary constriction of blood vessels following subarachnoid hemorrhage (SAH), which can lead to stroke. This study investigated interactions between localization of vasospasm in the CoW, vasospasm severity, anatomical variations, and changes in collateral flow directions. Patient-specific computational fluid dynamics (CFD) simulations were created for 25 vasospasm patients. Computed tomographic angiography scans were segmented capturing the anatomical variation and stenosis due to vasospasm. Transcranial Doppler ultrasound measurements of velocity were used to define boundary conditions. Digital subtraction angiography was analyzed to determine the directions and magnitudes of collateral flows as well as vasospasm severity in each vessel. Percent changes in resistance and viscous dissipation were analyzed to quantify vasospasm severity and localization of vasospasm in a specific region of the CoW. Angiographic severity correlated well with percent changes in resistance and viscous dissipation across all cerebral vessels. Changes in flow direction were observed in collateral pathways of some patients with localized vasospasm, while no significant changes in flow direction were observed in others. CFD simulations can be leveraged to quantify the localization and severity of vasospasm in SAH patients. These factors as well as anatomical variation may lead to changes in collateral flow directions. Future work could relate localization and vasospasm severity to clinical outcomes like the development of infarct.

A 53-year-old female underwent a lung ventilation/perfusion scintigraphy (V/Q scan) in the workup of extensive thrombosis of the left subclavian and internal jugular veins. The perfusion lung scan visualized an atypical uptake in the thoracic vertebrae. A chest Computed Tomography (CT) scan demonstrated unusual tortuous and opacified thoracic superficial veins, collaterals of the lateral thoracic vein. Many venous collateral pathways can be developed in the case of superior vena cava syndrome. 99mTc-macroaggregated albumin particles may pass through the lateral thoracic vein and eventually through the vertebral venous plexus before being finally trapped by the vertebral capillaries. Besides right-to-left shunting, extrapulmonary uptake in the lung perfusion scintigraphy is very rare and may be used by collateral venous pathways.

UNASSIGNED: Parent artery occlusion (PAO) with or without bypass surgery is a feasible treatment for large intracavernous carotid artery (ICCA) aneurysms. The ideal occlusion site (internal or common carotid artery [CCA]) and ischemic complications after PAO have received special attention since the description of the technique. Unfrequently, some patients can also develop unusual external carotid artery-internal carotid artery collateral pathways distal to the ligation site that can explain the failure to aneurysm size reduction.
UNASSIGNED: We describe a rare case of delayed refilling of a large ICCA aneurysm partially thrombosed which early recanalized after surgical ligation of the cervical CCA through an unusual collateral pathway.
UNASSIGNED: Based on our experience, we recommend periodic long-term follow-up neuroimaging, especially in those cases where potential collateral branches have not been clearly identified in the preoperative studies.

A collateral pathway established after lymphadenectomy could play an important role in long-term lymphedema treatment. The present study investigated alterations of lymph dynamics 1 year after lymphadenectomy using indocyanine green fluorescent lymphography to determine if a collateral pathway may be used for long-term lymphedema treatment. Wistar rats were anaesthetized and lymph nodes were excised at the inguinal and popliteal fossae. The treated hind limb was evaluated by fluorescent lymphography between 10 weeks and 6 months and between 6 months and 1 year postoperatively. Fluorescent lymphography demonstrated a lymphatic pathway to the ipsilateral axillary fossa in all rats 1 year after lymphadenectomy. Some capillary branches in the paths leading to the ipsilateral axillary fossa were dilated and tortuous. In addition, areas in which a fluorescent signal was not visible were increased in the thigh. In conclusion, the collateral pathway did not appear to be only for temporary use to compensate for drainage from the edematous limb but appears more stable as a component of a compensating lymphatic system. These new dilated vessels, although functional at this point, may still be susceptible to disturbance by further alteration to the lymph vessels.

Congenital absence of internal carotid artery (ICA) is a rare anomaly seen in around 0.01% of the population. High incidence of aneurysms is reported in these patients population. Many patients are asymptomatic as the development of a collateral circulation ensures cerebral perfusion. The embryology, the common collateral pathways, and the imaging findings associated with this anomaly are illustrated with 2 new cases. We reported the cases of 2 totally asymptomatic patients at the time of imaging in which ICA agenesis was proved on computed tomography angiography. On imaging, all the most important findings necessary for ICA agenesis diagnosis have been identified and described. Noninvasive imaging techniques are currently the mainstay of ICA agenesis diagnosis.

Collateral pathways in aortoiliac occlusive disease are essential for arterial blood flow to the abdomen, pelvis, and lower extremities. These pathways can be broadly divided into systemic-systemic, visceral-visceral, and systemic-visceral collateral networks. MDCT angiography is the most commonly used modality for the diagnostic evaluation of patients with aortoiliac occlusive disease, allowing excellent evaluation of stenotic arterial segments, as well as beautifully illustrating resulting collateral pathways (particularly when utilizing 3D reconstruction techniques). This article seeks to familiarize radiologists with the most common patterns of aortoiliac occlusion and associated arterial collateral pathways utilizing CT angiography.

The purpose of this article is to describe the various portosystemic collateral pathways pertinent to portal hypertension on multi-detector row computed tomography (MDCT) and their clinical relevance, with special emphasis on the uncommon ones. The knowledge and understanding of the various patterns of portosystemic collateral channels has important implications both for the clinician and the interventionist. MDCT with its advanced post processing capabilities can exquisitely demonstrate these vascular pathways to help in therapeutic decision making. Teaching points • Portosystemic collaterals are an important cause of bleeding and hepatic encephalopathy. • Radiologists should be familiar with the imaging findings to effectively identify them. • Pre-operative knowledge of portosystemic collaterals is essential to avoid inadvertent vascular injury.

Presence of portosystemic collateral veins (PSCV) is common in portal hypertension due to cirrhosis. Physiologically, normal portosystemic anastomoses exist which exhibit hepatofugal flow. With the development of portal hypertension, transmission of backpressure leads to increased flow in these patent normal portosystemic anastomoses. In extrahepatic portal vein obstruction collateral circulation develops in a hepatopetal direction and portoportal pathways are frequently found. The objective of this review is to illustrate the various PSCV and portoportal collateral vein pathways pertinent to portal hypertension in liver cirrhosis and EHPVO.

We present a rare case of spontaneous trans-splenic shunt and intra-splenic collaterals in a patient with liver cirrhosis and portal hypertension. The shunt and presence of cirrhosis and portal hypertension was incidentally detected by abdominal computed tomographic imaging during evaluation for abdominal pain. There has been a single report on the presence of trans-splenic shunt in two children with extra-hepatic portal venous obstruction but no cases that report intra-splenic collaterals: to the best of our knowledge, this is the first reported case of spontaneous trans-splenic shunt in the presence of intra-splenic collaterals and incidental multiple splenic artery aneurysms that developed in an adult with compensated cirrhosis and portal hypertension.

OBJECTIVE: To describe and propose a sonographic classification of the blood-draining pathways of obstructed hepatic veins in Budd-Chiari syndrome.
METHODS: This retrospective study included 206 patients with hepatic vein obstructions who underwent sonographic examination. We evaluated the afflicted hepatic veins, as well as the course, orifice, blood flow direction of draining veins, and communicating branches. Results were classified and compared with digital subtraction angiography and computed tomography angiography.
RESULTS: Of 618 hepatic veins in 206 patients, 542 were obstructed. The blood-draining pathways were classified as hepatic vein-accessory hepatic vein (131/206), hepatic vein-hepatic vein/accessory hepatic+hepatic vein (49/206), and, less frequently, collateral pathways (26/206). Blood was drained from obstructed hepatic veins to the inferior vena cava, right atrium, para-umbilical veins, or hepatic subcapsular veins through communicating branches of various number and diameters. Doppler signals were obtained from the draining veins.
CONCLUSIONS: Sonography provides accurate information regarding the blood-draining pathways of obstructed hepatic veins in Budd-Chiari syndrome, which may be helpful for treatment and follow-up.