The azygos venous system is a crucial conduit of the posterior thorax and potentially vital collateral pathway. However, it is often overlooked clinically and radiologically. This pictorial essay reviews the normal azygos venous anatomy and CT findings of congenital variations and structural changes associated with acquired pathologies.
기정맥계는 후방 흉부의 중요한 부속 정맥이며 측부순환으로서 중대한 역할을 한다. 그러나, 그 중요성에도 불구하고 임상적 혹은 영상의학적으로 종종 간과된다. 본 임상화보에서는, 기정맥계의 정상 해부학에 대해 알아보고, 기정맥계에서 볼 수 있는 다양한 선천 변이와 후천적 질환에 따른 구조 변화의 CT 소견에 대하여 검토하고자 한다.

A 59-year-old male was transported to the emergency department by ambulance with complaints of left-sided abdominal pain. Blood gas analysis revealed elevated lactate, and plain computed tomography revealed no bowel ischemic change. Contrast-enhanced computed tomography revealed isolated superior mesenteric artery dissection with mildly stenosed true lumen. The patient was treated with conservative management on admission. Staged fluid intake, oral prescriptions, and diet were commenced with attention to the symptoms. After four days of hospitalization, the patient was discharged with a stable condition. However, the patient returned to our hospital complaining of left lower back pain three hours after discharge. Contrast-enhanced computed tomography revealed an enlarged false lumen with a moderately stenosed true lumen. After a thorough discussion between vascular surgeons and interventional radiologists, conservative management was commenced on the second admission. The clinical course was uneventful, with proof of improved imaging findings.

A 59-year-old male presented to the emergency department with distressing epigastric pain after seeking medical attention at a nearby clinic three hours prior. Upon examination, the attending physician noticed edematous changes in the proximal segment of the superior mesenteric artery, and a subsequent enhanced computed tomography (CT) scan confirmed the diagnosis of an isolated dissection of the artery. Notably, the true lumen of the vessel was significantly narrowed, raising concerns for potential vascular compromise. After extensive consultation between a vascular surgeon and a radiologist, a decision was made to adopt a conservative management approach. The patient was closely monitored with meticulous bowel rest, hydration management, and carefully curated dietary modifications. Over time, subsequent CT scans revealed progressive enlargement of the true lumen, which was highly reassuring to the medical team. As a result of the expert management and diligent care provided, the patient was eventually discharged home without any adverse events or complications. This case highlights the critical role of a multidisciplinary approach in managing complex vascular pathology and underscores the importance of thoughtful clinical decision-making and meticulous monitoring in achieving favorable outcomes.

Identification of the Adamkiewicz\'s artery (AKA) prior to the operation is one of the spinal cord ischaemia preventive measures. A 75-year-old man presented with the rapid expansion of thoracic aortic aneurysm. Collateral vessels from the right common femoral artery to the AKA were observed on preoperative computed tomography angiography. The stent graft was successfully deployed through the contralateral side via a pararectal laparotomy to avoid collateral vessel injury supplying the AKA. This case highlights the significance of preoperative identification of collateral vessels to the AKA.

We describe a patient in whom the deep inferior epigastric artery served as a collateral pathway to the lower extremities, and free latissimus dorsi myocutaneous flap transfer was successfully used for reconstruction instead of the originally planned free rectus abdominis myocutaneous flap. A 74-year-old woman underwent subtotal tongue resection, followed by free flap tongue reconstruction for tongue cancer. Reconstruction using a free rectus abdominis myocutaneous flap was considered; however, preoperative contrast-enhanced computed tomography revealed complete occlusion of the bilateral external iliac arteries. Doppler ultrasonography revealed retrograde blood flow via the deep inferior epigastric artery, and the internal thoracic artery-deep inferior epigastric artery pathway served as a collateral pathway that supplied the lower extremities. The patient underwent reconstructive surgery using a free latissimus dorsi myocutaneous flap, and the flap completely survived. The internal thoracic artery-deep inferior epigastric artery pathway serves as a critical collateral pathway to the lower extremities in patients with aortoiliac occlusive disease. Blockage of the deep inferior epigastric artery in patients in whom this vessel shows retrograde blood flow may result in lower extremity ischemia. Therefore, preoperative Doppler ultrasonography is warranted to confirm the direction of the blood flow, in addition to evaluation of the deep inferior epigastric artery and its perforators before planning rectus abdominis myocutaneous flap or deep inferior epigastric artery perforator flap surgery.

Common carotid artery occlusion (CCAO) is a rare phenomenon associated with the development of neurological symptoms. In CCAO, diversion of blood flow from the external carotid artery (ECA) to the internal carotid artery (ICA) via the carotid bulb (CB) may occur. This pathway activation has been called \"carotid steal\". Starting from a particular case we describe the ECD finding of a complete occlusion of CCA with patency of ICA and ECA. In case of occlusion of CCA, inversion of the ECA flow may occur, towards the ICA, and it can be damped by a significant stenosis crossed in retrograde direction that may concur to maintain the pressure balance between the two circulations. Usually, this particular compensation can guarantee normal flow velocities in middle cerebral arteries without signs of activation of anterior collateral pathways. In this review we underline the protective role of ECA and we propose a new definition for this phenomenon. The ECA may provide blood to the cerebral circulation through several anastomotic secondary channels. Finally, only with an extensive knowledge of hemodynamic information of all intracranial and extracranial arteries, including ECA, we can estimate cerebral ischemic risk of the patient and choose the correct management of this occlusion.

BACKGROUND: The collateral pathways between the superior mesenteric artery (SMA) and inferior mesenteric artery (IMA) play an important role in colonic surgery. The most well-known are the Drummond marginal artery and Riolan\'s arch. The Moskowitz artery, also known as the meandering mesenteric artery, is a lesser-known collateral pathway and represents another link between SMA and IMA. The Moskowitz artery runs along the colonic mesentery floor and represents the link between the proximal segment of the middle colic artery and the ascending branch of the left colic artery.
OBJECTIVE: To comprehend the presence and importance of the Moskowitz artery (meandering mesenteric artery) in preoperative patients by using computed tomography (CT) studies.
METHODS: We retrospectively reviewed all abdominal CT images performed using intravenous contrast for any reason at the Radiology Department of Yeditepe University Hospital between April 2015 and September 2018. Patients older than 18 years with intravenous contrast (arterial and venous phases with a cross-section thickness of 0.625 mm), who underwent abdominal CT scan, and patients without any abdominal surgery were included in the study. As a result of the screening, 109 CT scans with eligibility criteria were included in this study.
RESULTS: There were 109 cases in this study; 50 (45.9%) of them were male and 59 (54.1%) were female. Moskowitz artery was found in 18 (16.5%) cases; 8 were males and 10 were females. Riolan\'s arch was present in 30 cases, of whom 15 were male and 15 were female. In our study Moskowitz artery and Riolan\'s arch were monitored as separate vascular structures, and in all cases with Moskowitz artery, Riolan\'s arch was also present. There was a statistically significant difference (p < 0.05) between the combined MCA emerging type and the presence of MA, and 12 cases with combined branch and 6 cases with single branch had Moskowitz artery. There was a statistically significant difference (p < 0.05) between LCA types and the presence of MA, and the Moskowitz artery was the most common seen at type 1 LCA.
CONCLUSIONS: Knowledge of the relationship between Riolan\'s arch and the Moskowitz artery is valuable, and preoperative evaluation of this artery may be beneficial in the presence of Riolan\'s arch. In addition, preoperative radiological evaluation and its importance are prominent in minimising intraoperative bleeding during splenic flexure mobilisation with a medial laparoscopic approach and reducing the risk of colorectal anastomosis leakage.

Multidetector computed tomographic angiography (MDCTA) is the new gold standard for diagnostic evaluation of the abdominal and/or mesenteric arteries. It is not invasive and provides a 2D and 3D global cartography of all abdominal arteries and that with only a limited amount of contrast media. MDCTA allows the optimal diagnosis of single or multiple arterial stenosis and easily analyses sometimes very complex collateral pathways. It constitutes a major advance to plan the arterial visceral safety of major commonly performed abdominal surgical procedures such as aorto-iliac surgery, endovascular aneurysm repair (EVAR), but also complex pancreatic and gastrointestinal or colonic surgery. It also allows to plan the most optimal strategy for revascularization of the mesenteric system through percutaneous angioplasty, stent placement or surgical bypass. This extensive pictorial review illustrates a large variety of situations which may be found during clinical practise. Single compression or stenosis of each digestive artery, combined and/or complex associations of stenosis and/or compressions of several arteries, secondary complications like aneurysms and classical but also sometimes unusual patterns of collateralization are richly illustrated. Specific syndromes comprising the median arcuate ligament syndrome (MALS) and the Leriche\'s syndrome are also discussed.

The pelvic collateral system is a robust network of communicating vessels that provide the functional reserve to withstand chronic aorto-iliac occlusive disease. For establishment of collateral circulation, the afferent vessel must originate proximal to the occlusion and anastomose with vessel/s distal to the occlusion. These collateral pathways can be classified as viscero-systemic, systemic-systemic, and visceral-visceral. CT angiography (CTA) is often the initial modality for evaluating patients with atherosclerotic vascular disease, because it is non-invasive and has been shown to be comparable to conventional angiography. Most collateral pathways are well demonstrated on CTA, which therefore is a useful tool for preoperative planning and regional interventional procedures.

BACKGROUND: While hemodynamic stress can result in aneurysm formation, it rarely contributes to the development of peripheral aneurysms in collateral pathways. We report two patients with ruptured distal aneurysms in a collateral pathway associated with stenosis of a major cerebral artery.
METHODS: A 67-year-old man presented with intracerebral hemorrhage in the right frontal lobe. Digital subtraction angiography (DSA) revealed severe stenosis of the right middle cerebral artery and two aneurysms in the collateral pathway of the right anterior cerebral artery. The ruptured aneurysm was trapped and resected; histologically, it was a true saccular aneurysm. The unruptured aneurysm was clipped and the patient was discharged without additional neurological deficits. The second patient was a 73-year-old woman with subarachnoid hemorrhage. DSA revealed three arterial dilations. On the 7(th) day of hospitalization, one of the aneurysms in a posterior inferior cerebellar artery-anterior inferior cerebellar artery anastomosis that functioned as a collateral pathway in the presence of severe basilar artery stenosis was found to be enlarged. It was treated by selective aneurysmal coil embolization with parent artery preservation. Her postoperative course was uneventful and she was discharged without any neurological deficits.
CONCLUSIONS: We document the successful treatment of two patients with ruptured aneurysms in the peripheral portion of a collateral pathway. We discuss the histology of peripheral aneurysms and present a review of the literature.