Focused ultrasound neuromodulation of the spleen activates an anti-inflammatory response in humans.

Focused ultrasound stimulation (FUS) activates mechanosensitive ion channels and is emerging as a method of noninvasive neuromodulation. In preclinical studies, FUS of the spleen (sFUS) activates an anti-inflammatory neural pathway which suppresses acute and chronic inflammation. However, the relevance of sFUS for regulating inflammatory responses in humans is unknown. Here, we used a modified diagnostic ultrasound imaging system to target the spleen of healthy human subjects with 3 min of continuously swept or stationary focused pulsed ultrasound, delivered at three different energy levels within allowable safety exposure limits. Potential anti-inflammatory effects of sFUS were assessed by measuring sFUS-elicited changes in endotoxin-induced tumor necrosis factor (TNF) production in whole blood samples from insonified subjects. We found that stimulation with either continuously swept or focused pulsed ultrasound has an anti-inflammatory effect: sFUS lowers TNF production for >2 h, with TNF returning to baseline by 24 h following sFUS. This response is independent of anatomical target (i.e., spleen hilum or parenchyma) or ultrasound energy level. No clinical, biochemical, or hematological parameters are adversely impacted. This is the first demonstration that sFUS suppresses the normal inflammatory response in humans, with potential implications for noninvasive bioelectronic therapy of inflammatory disorders.

International consensus conference recommendations on ultrasound education for undergraduate medical students.

OBJECTIVES: The purpose of this study is to provide expert consensus recommendations to establish a global ultrasound curriculum for undergraduate medical students. METHODS: 64 multi-disciplinary ultrasound experts from 16 countries, 50 multi-disciplinary ultrasound consultants, and 21 medical students and residents contributed to these recommendations. A modified Delphi consensus method was used that included a systematic literature search, evaluation of the quality of literature by the GRADE system, and the RAND appropriateness method for panel judgment and consensus decisions. The process included four in-person international discussion sessions and two rounds of online voting. RESULTS: A total of 332 consensus conference statements in four curricular domains were considered: (1) curricular scope (4 statements), (2) curricular rationale (10 statements), (3) curricular characteristics (14 statements), and (4) curricular content (304 statements). Of these 332 statements, 145 were recommended, 126 were strongly recommended, and 61 were not recommended. Important aspects of an undergraduate ultrasound curriculum identified include curricular integration across the basic and clinical sciences and a competency and entrustable professional activity-based model. The curriculum should form the foundation of a life-long continuum of ultrasound education that prepares students for advanced training and patient care. In addition, the curriculum should complement and support the medical school curriculum as a whole with enhanced understanding of anatomy, physiology, pathophysiological processes and clinical practice without displacing other important undergraduate learning. The content of the curriculum should be appropriate for the medical student level of training, evidence and expert opinion based, and include ongoing collaborative research and development to ensure optimum educational value and patient care. CONCLUSIONS: The international consensus conference has provided the first comprehensive document of recommendations for a basic ultrasound curriculum. The document reflects the opinion of a diverse and representative group of international expert ultrasound practitioners, educators, and learners. These recommendations can standardize undergraduate medical student ultrasound education while serving as a basis for additional research in medical education and the application of ultrasound in clinical practice.

Bead-anchored surgical templates for static computer-assisted implant surgery: A dental technique.

This technique report describes an alternative method to stabilize surgical templates throughout full-arch static computer-assisted implant surgery (FA s-CAIS). In FA s-CAIS, remaining teeth, mucosa, existing implants, custom occlusal device, bone, or any combination thereof, could be used as an initial positioning mechanism to position surgical templates. Different anchoring mechanisms are then used to stabilize the surgical templates during surgery. In this report, a novel design of surgical templates using remaining dentition and opposing occlusal surfaces as initial positioning mechanism followed by the combination of bone block fixation screw and stainless-steel beads as secondary anchoring mechanisms is described. The advantages, limitations, and comparisons with surgical templates using other anchoring mechanisms are also discussed.

Manifestations of Sickle Cell Disorder at Abdominal and Pelvic Imaging.

Sickle cell disorder (SCD) refers to a spectrum of hematologic disorders that cause a characteristic clinical syndrome affecting the entire body. It is the most prevalent monogenetic hemoglobinopathy worldwide, with a wide range of focal and systemic expressions. Hemoglobin gene mutation leads to the formation of abnormal sickle-shaped red blood cells, which cause vascular occlusion and result in tissue and organ ischemia and infarction. Recurrent episodes of acute illness lead to progressive multisystem organ damage and dysfunction. Vaso-occlusion, hemolysis, and infection as a result of functional asplenia are at the core of the disease manifestations. Imaging plays an essential role in the diagnosis and management of SCD-related complications in the abdomen and pelvis. A thorough understanding of the key imaging findings of SCD complications involving hepatobiliary, gastrointestinal, genitourinary, and musculoskeletal systems is crucial to timely recognition and accurate diagnosis. The authors aim to familiarize the radiologist with the SCD spectrum, focusing on the detection and evaluation of manifestations that may appear at imaging of the abdomen and pelvis. The topics the authors address include (a) the pathophysiology of the disease, (b) the placement of SCD among hemoglobinopathies, (c) the clinical presentation of SCD, (d) the role of imaging in the evaluation and diagnosis of patients with SCD who present with abdominal and pelvic manifestations in addition to extraperitoneal manifestations detectable at abdominal or pelvic imaging, (e) imaging features associated with common and uncommon sequelae of SCD in abdominal and pelvic imaging studies, and (f) a brief overview of management and treatment of patients with SCD. Online supplemental material is available for this article. ©RSNA, 2022.

Pathologic Conditions at Imaging of the Spermatic Cord.

A wide range of benign and malignant processes can affect the spermatic cord (SC). Familiarity with and recognition of the characteristic imaging features of these entities are imperative for accurate diagnosis and optimal clinical care. While some SC diseases are self-limiting, others can result in infertility and potentially life-threatening infection or bleeding if they are left untreated. Therefore, correct diagnosis is important for life-saving treatment and preservation of fertility. Disorders including anomalies of the vas deferens and the processus vaginalis, arterial and venous diseases (torsion of the SC and varicoceles), infection, trauma, and neoplasms are the most pertinent entities with which radiologists should be familiar when assessing the SC. Knowing what to expect in a patient who has undergone SC interventions is imperative. US has a fundamental role in the initial examination of patients who present with symptoms that indicate abnormalities of the SC, such as suspected posttraumatic testicular retraction or SC torsion. Other imaging techniques including abdominal and pelvic MRI and CT have their own importance. For correct interpretation of the findings and to establish an accurate diagnosis, it is crucial to have a thorough knowledge of the anatomy, the utility and limitations of various imaging modalities, optimal imaging and scanning techniques, and the imaging features of various benign and malignant pathologic conditions that can involve the SC. Online supplemental material is available for this article. ©RSNA, 2022.

Use of Methotrexate in Gynecologic and Obstetric Practice: What the Radiologist Needs to Know.

Methotrexate (MTX) is the primary pharmaceutical agent that is used for management of disorders arising from trophoblastic tissue. Its widespread international use is mostly attributable to its noninvasive, safe, and effective characteristics as a treatment option for ectopic pregnancy (EP) and gestational trophoblastic disease (GTD), with the large added benefit of fertility preservation. Although the effects of MTX usage are well documented in the gynecologic and obstetric literature, there is a scarcity of radiologic literature on the subject. Depending on the type of EP, the route of MTX administration and dosage may vary. US plays an essential role in the diagnosis and differentiation of various types of EPs, pregnancy-related complications, and complications related to MTX therapy, as well as the assessment of eligibility criteria for MTX usage. A knowledge of expected imaging findings following MTX treatment, including variability in echogenicity and shape of the EP, size fluctuations, changes in vascularity and gestational sac content, and the extent of hemoperitoneum, is essential for appropriate patient management and avoidance of unnecessary invasive procedures. A recognition of sonographic findings associated with pregnancy progression and complications such as tubal or uterine rupture, severe hemorrhage, septic abortion, and development of arteriovenous communications ensures prompt patient surgical management. The authors discuss the use of MTX in the treatment of disorders arising from trophoblastic tissue (namely EP and GTD), its mechanism of action, its route of administration, and various treatment regimens. The authors also provide a focused discussion of the role of US in the detection and diagnosis of EP and GTD, the assessment of the eligibility criteria for MTX use, and the identification of the sonographic findings seen following MTX treatment, with specific emphasis on imaging findings associated with MTX treatment success and failure. Online supplemental material is available for this article. ©RSNA, 2021.

Optimization of duplex velocity criteria for diagnosis of internal carotid artery (ICA) stenosis: A report of the Intersocietal Accreditation Commission (IAC) Vascular Testing Division Carotid Diagnostic Criteria Committee.

Diagnostic criteria to classify severity of internal carotid artery (ICA) stenosis vary across vascular laboratories. Consensus-based criteria, proposed by the Society of Radiologists in Ultrasound in 2003 (SRUCC), have been broadly implemented but have not been adequately validated. We conducted a multicentered, retrospective correlative imaging study of duplex ultrasound versus catheter angiography for evaluation of severity of ICA stenosis. Velocity data were abstracted from bilateral duplex studies performed between 1/1/2009 and 12/31/2015 and studies were interpreted using SRUCC. Percentage ICA stenosis was determined using North American Symptomatic Carotid Endarterectomy Trial (NASCET) methodology. Receiver operating characteristic analysis evaluated the performance of SRUCC parameters compared with angiography. Of 448 ICA sides (from 224 patients), 299 ICA sides (from 167 patients) were included. Agreement between duplex ultrasound and angiography was moderate (κ = 0.42), with overestimation of degree of stenosis for both moderate (50-69%) and severe (⩾ 70%) ICA lesions. The primary SRUCC parameter for ⩾ 50% ICA stenosis of peak-systolic velocity (PSV) of ⩾ 125 cm/sec did not meet prespecified thresholds for adequate sensitivity, specificity, and accuracy (sensitivity 97.8%, specificity 64.2%, accuracy 74.5%). Test performance was improved by raising the PSV threshold to ⩾ 180 cm/sec (sensitivity 93.3%, specificity 81.6%, accuracy 85.2%) or by adding the additional parameter of ICA/common carotid artery (CCA) PSV ratio ⩾ 2.0 (sensitivity 94.3%, specificity 84.3%, accuracy 87.4%). For ⩾ 70% ICA stenosis, analysis was limited by a low number of cases with angiographically severe disease. Interpretation of carotid duplex examinations using SRUCC resulted in significant overestimation of severity of ICA stenosis when compared with angiography; raising the PSV threshold for ⩾ 50% ICA stenosis to ⩾ 180 cm/sec as a single parameter or requiring the ICA/CCA PSV ratio ⩾ 2.0 in addition to PSV of ⩾ 125 cm/sec for laboratories using the SRUCC is recommended to improve the accuracy of carotid duplex examinations.

Medical Student Ultrasound Education: The Radiology Chair Weighs In.

ABSTRACT: To assess the radiology department chairs' opinions concerning current status and plans for teaching ultrasound to medical students, the American College Taskforce on Radiology Ultrasound Education, commissioned by the American College of Radiology, distributed a survey to 142 radiology chairs and a medical school dean subgroup.The response rate was 30% (42/142), and 76% indicated ultrasound was currently part of the medical student curriculum. In preclinical years, radiology involvement was only 6.4%. During clinical years, radiology led ultrasound education with 51.7% in general and 82.9% in elective rotations. Regarding actual content, top 4 results were evenly distributed between learning hands-on scanning (81.1%), diagnostic use of ultrasound (75.7%), anatomy/pathology (75.7%), and ultrasound guidance for procedures (54.0%). Educational leaders in preclinical courses were emergency medicine (72.7%) followed by radiology (45.4%) physicians. During clinical years, leaders were radiology (52.6%) and emergency medicine (47.4%) physicians. Most chairs stated that knowledge of diagnostic ultrasound should be mandatory (76.2%), stressing the importance of teaching the diagnostic capabilities and uses of ultrasound as the primary goal (78.8%). Perceived barriers to implementation were evenly distributed between lack of space in the curriculum (55.6%), lack of faculty (48.2%), lack of resources (44.4%), and lack of institutional support (40.7%). The American College Taskforce on Radiology Ultrasound Education survey shows that radiology's role in ultrasound undergraduate education occurs almost exclusively during clinical years, and the chairs voice a desire to improve upon this role. Barriers include both intradepartmental (faculty and resources) and institutional (curricular) factors.

Gel Rounds: Integrating Bedside Ultrasound Training for Third-Year Medical Students Into the Internal Medicine Clerkship.

Despite formal ultrasound training becoming prevalent in preclinical medical student education, significant barriers remain to the continuation of this training during clinical years. We sought to develop a program for third-year medical students to continue ultrasound training after an already robust preclinical ultrasound curriculum and evaluate their scanning confidence after participation. We developed a program to facilitate bedside ultrasound scanning of patients being cared for by third-year students. Students identified appropriate patients to be scanned, obtained consent for scanning, and determined which scans were most appropriate given the patient's clinical problems. Trained facilitators met with students at the bedside in 1-hour sessions called Gel Rounds to observe and direct the students' scans of their patients. Fifty-one students were surveyed after completing Gel Rounds. Students were significantly more likely to feel comfortable with independently acquiring and interpreting images after Gel Rounds than before completing the activity. Approximately 67% of students felt that ultrasound had utility in assisting bedside clinical reasoning, and this proportion did not change significantly after completing Gel Rounds. Gel Rounds was a positive continuation of the ultrasound curriculum into the third-year clerkship environment. A minority of students reported prior ultrasound exposure in their third year, reflecting difficulty with developing a longitudinal curriculum. The activity helped students to independently acquire and interpret images in patients. Because Gel Rounds can be performed at the discretion of students and faculty, it fits naturally in a variety of existing longitudinal curricula.

Multisystem Imaging Manifestations of COVID-19, Part 2: From Cardiac Complications to Pediatric Manifestations.

Infection with severe acute respiratory syndrome coronavirus 2 results in coronavirus disease 2019 (COVID-19), which was declared an official pandemic by the World Health Organization on March 11, 2020. COVID-19 has been reported in most countries, and as of August 15, 2020, there have been over 21 million cases of COVID-19 reported worldwide, with over 800 000 COVID-19-associated deaths. Although COVID-19 predominantly affects the respiratory system, it has become apparent that many other organ systems can also be involved. Imaging plays an essential role in the diagnosis of all manifestations of the disease and its related complications, and proper utilization and interpretation of imaging examinations is crucial. A comprehensive understanding of the diagnostic imaging hallmarks, imaging features, multisystem involvement, and evolution of imaging findings is essential for effective patient management and treatment. In part 1 of this article, the authors described the viral pathogenesis, diagnostic imaging hallmarks, and manifestations of the pulmonary and peripheral and central vascular systems of COVID-19. In part 2 of this article, the authors focus on the key imaging features of the varied pathologic manifestations of COVID-19, involving the cardiac, neurologic, abdominal, dermatologic and ocular, and musculoskeletal systems, as well as the pediatric and pregnancy-related manifestations of the virus. Online supplemental material is available for this article. ©RSNA, 2020.

Multisystem Imaging Manifestations of COVID-19, Part 1: Viral Pathogenesis and Pulmonary and Vascular System Complications.

Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) results in coronavirus disease 2019 (COVID-19), which was declared an official pandemic by the World Health Organization on March 11, 2020. The infection has been reported in most countries around the world. As of August 2020, there have been over 21 million cases of COVID-19 reported worldwide, with over 800 000 COVID-19-associated deaths. It has become apparent that although COVID-19 predominantly affects the respiratory system, many other organ systems can also be involved. Imaging plays an essential role in the diagnosis of all manifestations of the disease, as well as its related complications, and proper utilization and interpretation of imaging examinations is crucial. With the growing global COVID-19 outbreak, a comprehensive understanding of the diagnostic imaging hallmarks, imaging features, multisystemic involvement, and evolution of imaging findings is essential for effective patient management and treatment. To date, only a few articles have been published that comprehensively describe the multisystemic imaging manifestations of COVID-19. The authors provide an inclusive system-by-system image-based review of this life-threatening and rapidly spreading infection. In part 1 of this article, the authors discuss general aspects of the disease, with an emphasis on virology, the pathophysiology of the virus, and clinical presentation of the disease. The key imaging features of the varied pathologic manifestations of this infection that involve the pulmonary and peripheral and central vascular systems are also described. Part 2 will focus on key imaging features of COVID-19 that involve the cardiac, neurologic, abdominal, dermatologic and ocular, and musculoskeletal systems, as well as pediatric and pregnancy-related manifestations of the virus. Vascular complications pertinent to each system will be also be discussed in part 2. Online supplemental material is available for this article. ©RSNA, 2020.

Imaging Evaluation of Abdominopelvic Gunshot Trauma.

Firearm-related injuries, or gunshot wounds (GSWs), are among the most important worldwide public health problems, resulting in considerable annual morbidity, disability, and mortality. GSWs to the abdomen and pelvis are associated with substantial injuries to multiple organs and tissues. Imaging plays an important role in identifying these injuries, dictating nonoperative management, and determining imaging and clinical follow-up, as well as helping manage potential long-term complications. CT is the primary imaging modality used to evaluate these injuries and their complications, including use of reconstructed multiplanar volume-rendered images. The authors discuss the ballistics and mechanisms of firearm injury, CT findings, trajectory analysis, and applications of different imaging modalities above and beyond CT in evaluation of GSWs. Imaging findings and classifications of the severity of injuries to solid and hollow organs and vascular, musculoskeletal, and neurologic systems are reviewed. Key complications associated with gunshot injuries to the abdomen and pelvis are presented. The challenges of imaging in the acute trauma setting and potential pitfall mimics at imaging, particularly at CT, are also described. A step-by-step guide for thorough and comprehensive evaluation of GSWs to the abdomen and pelvis is introduced, with tips for optimizing effective communication with the clinical team. Online supplemental material is available for this article. ©RSNA, 2020.

Imaging Evaluation of Fallopian Tubes and Related Disease: A Primer for Radiologists.

A wide range of benign and malignant processes can affect one or both fallopian tubes. Familiarity with and recognition of the characteristic imaging features of these diseases and conditions are imperative for accurate diagnosis and prompt patient management. Disorders including pelvic inflammatory disease (hydrosalpinx and pyosalpinx in particular), isolated tubal torsion and ovarian torsion with fallopian tube involvement, endometriosis manifesting as hematosalpinx and adhesions, ectopic pregnancy, and malignancies are the most important entities that radiologists should be familiar with when assessing the fallopian tubes. Some fallopian tube diseases are self-limiting, while others can result in infertility or even potentially life-threatening infection or bleeding if left untreated. Therefore, correct diagnosis is important for appropriate life-saving treatment and preserving fertility. Understanding the physiologic features of the fallopian tube and the role of this organ in the pathogenesis of pelvic neoplasms is equally important. Knowledge of what to expect in a patient who has undergone uterine and fallopian tube interventions, such as uterine ablation and fallopian tube ligation, and of the potential associated complications (eg, postablation sterilization syndrome) also is pertinent. The imaging modalities used for the evaluation of fallopian tube disease and patency range from commonly used examinations such as US, CT, and MRI to other modalities such as hysterosalpingography and hysterosonography performed by using US contrast material. The ability to differentiate fallopian tube conditions from other adnexal and pelvic pathologic entities by using a variety of imaging modalities allows the radiologist to make a timely diagnosis and ensure proper clinical management. Online supplemental material is available for this article. ©RSNA, 2020.

Sonographic assessment of infectious diseases of the gastrointestinal tract: from scanning to diagnosis.

BACKGROUND: Sonography of the gastrointestinal (GI) tract is a practical, safe, inexpensive, and reproducible diagnostic tool for the evaluation, diagnosis, and follow-up of infectious bowel disease. The modality is rapidly gaining prominence among clinicians on a global scale. In the United States, however, ultrasound of the bowel remains underutilized primarily due to insufficient experience among radiologists and sonographers in performing sonographic bowel assessment. This lack of experience and knowledge results in misinterpretations, missed diagnoses, and underutilization of this modality in patients with acute abdomen, with the majority of GI pathology on sonography discovered incidentally. OBJECTIVES: This article aims to demonstrate the characteristic sonographic findings associated with GI infectious processes as well as provide dedicated ultrasound protocols for evaluation of the GI tract. CONCLUSION: This article serves a twofold purpose, raising awareness of the utility of this imaging modality within the radiology community and also providing practical teaching points for sonographic evaluation of infectious disorders of the GI tract.

The radiologist's guide to duplex ultrasound assessment of chronic mesenteric ischemia.

OBJECTIVE: This article reviews the relevant anatomy and physiology of the mesenteric vasculature, familiarizes the radiologist with the accepted diagnostic criteria for mesenteric artery stenosis and its role in the diagnosis of chronic mesenteric ischemia, describes Doppler imaging techniques, and provides protocols for the assessment and surveillance of the mesenteric vasculature before and after revascularization. It also discusses expected changes following revascularization and reviews common post-procedural complications. RESULTS: Duplex sonography plays an important role in the diagnosis and management of chronic mesenteric ischemia (CMI). Establishing a successful diagnosis is dependent upon knowledge of mesenteric arterial anatomy and physiology as well as sufficient expertise in image optimization and scanning techniques. Although there has been a trend toward utilization of other noninvasive [computed tomographic angiography (CTA), magnetic resonance angiography (MRA), and invasive (digital subtraction angiography (DSA)] imaging modalities for assessment of the mesenteric vasculature, a new era of "imaging wisely" raises legitimate concerns about the effects of ionizing radiation as well as potential effects of CT and MR contrast agents. These concerns are obviated by the use of ultrasound, and recently developed techniques, such as contrast-enhanced ultrasound and vascular applications focused on the evaluation of slow flow, have revealed the vast potential of vascular ultrasound in the evaluation of chronic mesenteric ischemia. CONCLUSION: Duplex sonography is a cost-effective and powerful tool that can be utilized for the accurate assessment of mesenteric vascular pathology, specifically mesenteric arterial stenosis, and for the evaluation of mesenteric arterial system post revascularization.

Optimizing Image Quality When Evaluating Blood Flow at Doppler US: A Tutorial.

Doppler US is an essential component of nearly all diagnostic US procedures. In this era of increased awareness of the effects of ionizing radiation and the side effects of iodine- and gadolinium-based contrast agents, Doppler US is poised to play an even bigger role in medical imaging. It is safe, cost-effective, portable, and highly accurate when performed by an experienced operator. The sensitivities and specificities of Doppler US for detecting blood flow and determining the direction and velocity of blood flow in various organs and vascular systems have increased dramatically in the past decade. With use of advanced flow techniques that are available for use with most modern equipment, US can provide vascular information that is comparable to or even more accurate than that obtained with other cross-sectional and interventional modalities. However, there remains concern that US (including newer more advanced flow-evaluating techniques) will not be used to its full potential owing to dependence on operator skill and expertise. Thorough understanding of image optimization techniques and expanded knowledge of the physical principles, instrumentation, application, advantages, and limitations of this modality are of utmost importance. The authors provide a simple practical guide for optimizing images for vascular flow detection by reviewing various cases and focusing on the parameters that should be optimized. Online supplemental material is available for this article. ©RSNA, 2019 See discussion on this article by Pellerito.

Ovarian dermoid cyst complicated by small bowel obstruction, entero-ovarian fistula formation, and malignant degeneration.

Dermoid cysts, or mature cystic teratomas, are complicated by malignant degeneration in only 1-2% of cases. Rarely, dermoid cysts result in complications of small bowel obstruction or entero-ovarian fistula formation. In the current report we present the case of a 59-year-old female with a known dermoid cyst who presented with leukocytosis and was discovered to have a small bowel obstruction at the level of an ileo-ovarian fistula. The patient was taken to the operating room and was treated with total abdominal hysterectomy, bilateral salpingo-oopherectomy, and short segment small bowel resection. Review of the surgical pathology revealed areas of malignant degeneration within the dermoid cyst to squamous cell carcinoma. To our knowledge, this is only the second reported case of an ovarian dermoid cyst complicated by small bowel obstruction, entero-ovarian fistula formation, and malignant degeneration.

An Interesting Observation Regarding Retrograde Vertebral Artery Flow in Patients With Dialysis Access Fistulas.

OBJECTIVES: Retrograde vertebral artery flow, the steal phenomenon, is most frequently caused by a flow-limiting stenosis of the proximal subclavian artery. The reversal of flow can be incomplete, resulting in bidirectional flow: retrograde in systole and antegrade in diastole. Less often, retrograde vertebral artery flow is the consequence of increased subclavian flow, as might occur with a well-functioning dialysis access fistula. Our objective was to evaluate bidirectional vertebral artery flow associated with dialysis access fistulas. METHODS: We retrospectively reviewed the direction of flow through the vertebral artery in systole and diastole of 335 patients with dialysis fistulas who had undergone extracranial cerebral vascular Doppler examinations. RESULTS: Fifteen patients had retrograde flow in their vertebral artery ipsilateral with the side of their fistula. There was completely reversed flow in 1 patient and bidirectional flow in the other 14. For each of these 14, the flow was antegrade in early systole and retrograde in diastole. Compression of the fistula restored the antegrade flow. CONCLUSIONS: Under conditions of reduced subclavian artery flow, bidirectional vertebral artery flow will be retrograde in early systole and antegrade in diastole. Under conditions of increased subclavian artery flow, bidirectional flow through the vertebral artery will be antegrade in early systole and retrograde in diastole.