Segmental arterial mediolysis of varying phases affecting both the intra-abdominal and intracranial vertebral arteries: an autopsy case report

Differentiating between segmental arterial mediolysis and other arterial vasculopathies to establish an early diagnosis - a systematic literature review and proposal of new diagnostic criteria

Segmental arterial mediolysis (SAM) is a rare vascular disease, characterized by acute but transient vulnerability of the wall of medium-sized arteries. The most characteristic feature of SAM is its biphasic course: an injurious phase marked by acute weakness of the arterial wall leading to acute dissection and/or hemorrhage, followed by a reparative phase in which granulation tissue and fibrosis restore the injured arterial wall. Residual stenosis, aneurysms, and/or arterial wall irregularities may remain visible on future imaging studies. Differentiating between SAM and other arterial vasculopathies is difficult due to its similarities with many other vascular diseases, such as vasculitis, fibromuscular dysplasia, inherited connective tissue disorders, and isolated visceral artery dissection. In this systematic review, we provide an overview on SAM, with an emphasis on the differential diagnosis and diagnostic work-up. We propose new diagnostic criteria to help establish a prompt diagnosis of SAM, illustrated by case examples from our multidisciplinary vascular clinic.

Segmental Arterial Mediolysis: A Multiguised Vasospastic Arteriopathy with Collateral Mesangial Cell Hyperplasia and Cardiac Toxicity Generated by Norepinephrine and Hyperdense Adrenoceptors Alone or by Crosstalk with Other Pressor Agents

Segmental arterial mediolysis (SAM), an uncommon vasospastic arteriopathy occurring in the muscular arteries innervated by the peripheral sympathetic nervous system, usually presents with catastrophic abdominal and retroperitoneal hemorrhages in elderly patients. SAM is initiated by the coupling of norepinephrine to plastically derived hyperdense foci of alpha-1 adrenergic receptors on the sarcolemma of arterial muscle. This ligand is created by stimuli signaled by iatrogenic sympathomimetic agonists, some beta-2 agonists, or an excessive release of adrenal catecholamines. Coupling of this ligand with cytoplasmic heterotrimeric Gq protein excessively signals a cascade of biochemical events generating two principal lesions of injurious-phase SAM-the shearing of the outer media from the adventitia and an overload of cytoplasmic calcium ions toxic to mitochondria causing mediolysis and/or apoptosis. The massive hemorrhages are caused by ruptured gap aneurysms created by the transmedial loss of the medial muscle. A norepinephrine-directed reparative response rapidly develops either resolving angiographic injurious lesions or creating a body of vascular disorders, the new guises of SAM with ischemic clinical profiles. These present in the epicardial, vertebral, intestinal, and retroperitoneal arteries, often in younger females as fibromuscular dysplasia, dissecting hematomas, and persistent aneurysms. Norepinephrine can crosstalk with other pressor agents to create SAM lesions-serotonin with idiopathic pulmonary hypertension and persistent pulmonary hypertension in the newborn, histamine in spontaneous coronary artery dissections with eosinophilia, and endothelin-1 in a field effect generated by SAM that creates venous fibromuscular dysplasia. Norepinephrine also participates in the collateral development of mesangial hyperplasia with focal segmental glomerulosclerosis and myocardial mediolysis and apoptosis in subjects with markedly elevated heart rates. Conclusion. Norepinephrine coupling with plastically elevated alpha-1 adrenoceptor or other pressor agents generates SAM, a histologically recognizable vasospastic arteriopathy, that with repair is transformed into several different standardized arterial diseases that alter SAM's clinical profile from a hemorrhagic to an ischemic disorder.

Segmental Arterial Mediolysis (SAM) Leading to Chronic Renal Insufficiency

Background

Segmental arterial mediolysis (SAM) is a rare self-limiting non-atherosclerotic, non-inflammatory vasculopathy. SAM typically affects the visceral arteries of the abdomen to include the celiac, mesenteric, and renal arteries. SAM has a favorable prognosis in most cases with an asymptomatic course but can have mortality rates as high as 50% due to acute aneurysmal rupture. Very few cases of adverse long-term sequelae involving SAM have been described, and this report of chronic kidney disease represents a sentinel case illustrating that chronic disease can and does occur as a result of SAM and should be investigated for at follow-up.

Case Presentation

In this case report, we describe a case of a 45-year-old male with erectile dysfunction but without any readily identifiable risk factors for chronic kidney disease (CKD) or vasculopathy, who presented with bilateral renal infarction and parenchymal infarcts due to SAM and who subsequently developed CKD at follow-up. We conduct a mini-literature review that discusses the pathogenesis of SAM in the context of vasospastic diseases, as well as compares the outcomes of observation-only, versus medical-management, versus endovascular-interventions in patients with SAM.

Conclusion

This is the first case to our knowledge of CKD occurring as an outcome of SAM without any preceding significant comorbidity, highlighting that whereas SAM is of itself rare and typically resolves, chronic disease can linger and should be evaluated for on follow-up. Further, we argue that radiological evidence of precursor vasospastic disease may exist in several locations apart from the index lesion and thus warrants wider whole-body radiographic exploration for lesions as an opportunity to prevent chronic sequelae as illustrated in this case report from occurring. Finally, a review of published case-series suggests that disease progression is less likely to occur after endovascular-intervention compared to observation-only or medical management and the risk of intervention vs conservative management should therefore be discussed with the patient.

Segmental arterial mediolysis: a commonly overlooked aetiology of acute abdominal pain

Segmental arterial mediolysis (SAM) is an uncommon condition and commonly missed diagnostic aetiology of acute abdominal pain, initially described in 1976. SAM is a non-inflammatory, non-atherosclerotic vasculopathy mostly involving the abdominal arteries with notable asymmetric involvement of the walls of the mesenteric arteries and their branches. Clinical presentation ranges from postprandial abdominal discomfort suggestive of mesenteric ischaemia to intra-abdominal bleeding. Pathophysiological explanation and prognosis of these cases are not well understood and therefore no clear guidelines for management exist. In this case report, we emphasise the imaging modalities used to reach the diagnosis and the management options available.

Segmental arterial mediolysis (SAM): Systematic review and analysis of 143 cases

Segmental arterial mediolysis (SAM) is a rare but serious nonatherosclerotic, noninflammatory vasculopathy of unknown etiology that often results in dissection, aneurysm, occlusion, or stenosis of, primarily, the abdominal arteries. Current literature lacks consensus on diagnostic criteria and management options for SAM. This review summarizes 143 cases and aims to advance appropriate recognition and management of SAM. Literature review of all relevant SAM case studies from 2005 to 2018 yielded 126 individual SAM cases from 66 reports. We identified 17 additional SAM cases from our center, bringing our analysis to 143 patients. Patients with SAM were most commonly men (68%) in their 60s. Hypertension (43%), tobacco use (12%), and hyperlipidemia (12%) were common comorbidities. Abdominal pain (80%) and intraabdominal bleeding (50%) were the most common presenting symptoms. Computed tomography was the most frequently used imaging method (78%), and histology was available in 44% of cases. The most commonly affected vessels were the superior mesenteric (53%), hepatic (45%), celiac (36%), renal (26%), and splenic (25%) arteries with aneurysm (76%), dissection (61%), and arterial rupture (46%). Treatments included coil embolization (28%), abdominal organ surgery (24%), open arterial repair (21%), and medical management (20%). Case-specific treatment modalities yielded symptom relief in the vast majority (91%) of patients, with a mortality rate of 7%.

Rare Mesenteric Arterial Diseases: Fibromuscular Dysplasia and Segmental Arterial Mediolysis and Literature Review

Fibromuscular dysplasia (FMD) and segmental arterial mediolysis (SAM) are noninflammatory, nonatherosclerotic arterial diseases that cause aneurysm, occlusion, and thromboses. These diseases are rarely seen in mesenteric arterial lesions; however, as they can be lethal if appropriate management is not provided, the accumulation of clinical information from cases is essential. We herein report the cases of a 57-year-old man diagnosed with FMD and a 63-year-old man diagnosed with SAM. We conclude that an early diagnosis with imaging modalities and clinical information followed by the appropriate treatment improves the prognosis of these arterial diseases.

A Ruptured Blood Blister-Like Aneurysm Associated with Intraperitoneal Hemorrhage due to Segmental Arterial Mediolysis: A Case Report and Literature Review

BACKGROUND

Segmental arterial mediolysis (SAM) is a rare non-atherosclerotic, noninflammatory vascular disease, characterized by mediolysis. We report an extremely rare case of subarachnoid hemorrhage (SAH) due to a ruptured blood blister-like aneurysm (BBA) of the internal carotid artery associated with SAM-related arteriopathy.

CASE DESCRIPTION

We experienced a case of SAH followed by intraperitoneal hemorrhage that occurred 12 days after the SAH onset. SAH was caused by a ruptured BBA of the internal carotid artery, which was treated by trapping with high-flow bypass. Intraperitoneal hemorrhage was caused by a rupture of a posterior inferior pancreaticoduodenal artery (PIPDA) aneurysm, which induced hypovolemic shock resulting in death in spite of endovascular internal trapping. Postmortem pathologic examination revealed that the PIPDA pseudoaneurysm was due to SAM.

CONCLUSIONS

We should pay attention to the association of SAM, which is a potentially life-threatening pathology when treating cerebral BBAs.

Arteriopathy of Unknown Etiology: Pathologic, Radiologic, and Cytogenetic Investigations

Patient: Male, 38

Final Diagnosis: Arteriopathy of unknown etiology

Symptoms: Left groin pain

Medication: —

Clinical Procedure: —

Specialty: Neurology

Unexpected intraabdominal hemorrhage due to segmental arterial mediolysis following subarachnoid hemorrhage: A case of ruptured intracranial and intraabdominal aneurysms

Background:

Segmental arterial mediolysis (SAM) is an uncommon vascular disease, which manifests as catastrophic intraabdominal hemorrhage caused by rupture of visceral dissecting aneurysms in most cases. The etiology of SAM is still unclear, but SAM may be a vasospastic disorder and the responsible pressor agent is norepinephrine. Recently, abdominal SAM coexisting with intracranial dissecting aneurysms has been reported, but the relationship between intraabdominal and intracranial aneurysms in SAM remains unclear, as no cases of concomitant abdominal SAM and ruptured intracranial saccular aneurysm have been reported.

Case Description:

A 49-year-old woman underwent emergent clipping for a ruptured saccular aneurysm at the left C1 portion of the internal carotid artery. Intraoperatively, norepinephrine was continuously administered intravenously under general anesthesia. Four days after the subarachnoid hemorrhage (SAH), the patient suddenly developed shock due to massive hematoma in the abdominal cavity. Imaging showed multiple aneurysms involving the splenic artery, gastroduodenal artery, common hepatic artery, and superior mesenteric artery. Coil embolization of the splenic artery was performed immediately to prevent bleeding. Subsequent treatment for cerebral vasospasm following SAH was performed with prevention of hypertension, and the patient recovered with left temporal lobe infarction. The diagnosis was abdominal SAM based on the clinical, imaging, and laboratory findings.

Conclusion:

Norepinephrine release induced by SAH and/or iatrogenic administration of norepinephrine may have promoted abdominal SAM in this case. Abdominal SAM may occur subsequent to rupture of ordinary saccular aneurysm, and may provoke catastrophic abdominal hemorrhage in the spasm stage after SAH.

A Case of Segmental Arterial Mediolysis Presenting as Mucosal Gastric Hematoma

Background

Although segmental arterial mediolysis (SAM) has been increasingly recognized as arteriopathy and there are some case reports about SAM, it is still very rare. It is characterized clinically by aneurysm, dissection, stenosis, and occlusion within splanchnic arterial branches, causing intra-abdominal hemorrhage or bowel ischemia. Mortality is as high as 50% in acute events.

Case Presentation

A 51-year-old man was referred to our hospital with hematemesis. Gastroscopy revealed a submucosal-like tumor on the posterior wall of gastric angle with ulceration. Computed tomography indicated a tumor measuring 65 × 50 mm in the stomach, which was suspected to have invaded into the pancreas. Significant hematemesis recurred; the patient developed shock and underwent emergency distal gastrectomy, distal pancreatectomy, and splenectomy. The pathology and the clinical course were compatible with SAM splenic artery rupture causing retroperitoneal hemorrhage that penetrated into the stomach. After that surgery, aneurysm of common hepatic artery ruptured and coil embolization was performed.

Conclusion

SAM is an important cause of intra-abdominal or retroperitoneal hemorrhage in patients without underlying disease. SAM typically presents as intra-abdominal hemorrhage, but, in this case, the retroperitoneal hemorrhage penetrated into the stomach and it looked like a submucosal tumor.

Subarachnoid and intraperitoneal hemorrhage secondary to segmental arterial mediolysis: A case report and review of the literature

Background Segmental arterial mediolysis (SAM) is an uncommon or underdiagnosed arteriopathy that presents with life-threatening hemorrhage. SAM can affect the intracranial, spinal, and visceral arteries, with reported cases of concomitant intracranial and visceral hemorrhage. Case description We present the case of a 61-year-old male with concurrent subarachnoid and intraperitoneal hemorrhage caused by simultaneously bleeding posterior spinal artery and splenic artery pseudoaneurysms. The posterior spinal artery pseudoaneurysms were treated with selective injection of polyvinyl alcohol particles into the posterior spinal artery, while the splenic artery pseudoaneurysm was treated with Gelfoam embolization. The constellation of imaging, clinical, and laboratory features led to a presumptive diagnosis of SAM, which remains the only reported cause of concurrent neurovascular and visceral artery aneurysm rupture. Conclusion SAM is a key diagnostic consideration in cases of concomitant intracranial, spinal, and visceral artery aneurysm rupture.

Fatal hemoperitoneum due to segmental arterial mediolysis

Spontaneous hemoperitoneum due to vascular injury is a life-threatening condition mostly associated with aortic or splanchnic arterial disease, which stems from atherosclerotic, inflammatory, or infectious origin. However, in 1976, Slavin and Gonzales described a nonatherosclerotic arterial disease that may render aneurysmal formation predominantly in the splanchnic arterial bed. The clinical presentation is diverse, but abdominal pain and shock prevail. We report the case of a middle-aged man who presented a hemoperitoneum due to a middle colic artery aneurysm rupture and died after undergoing a surgical treatment attempt. The preoperative imaging study revealed the presence of a huge hematoma in the epiplon retrocavity, and abdominal free liquid as well as extensive arterial disease with multiple aneurysms. The autopsy findings included hemoperitoneum, hematoma in the upper left abdominal quadrant, the surgical ligature of the middle colic artery, and histologic features consistent with segmental arterial mediolysis. The authors call attention to this rare entity and highlight the autopsy as a fundamental examination to accurately reach this diagnosis.

Longitudinal Evaluation of Segmental Arterial Mediolysis in Splanchnic Arteries: Case Series and Systematic Review

BACKGROUND

Segmental arterial mediolysis (SAM) is a rare non-atherosclerotic, non-inflammatory vascular disorder varying widely in clinical course. The purpose of this study is to analyze detailing clinical and imaging manifestations over time in patients with SAM through a literature review and to suggest an optimal management strategy.

METHODS

A retrospective review of eight consecutive patients diagnosed with SAM between January, 2000 and January, 2012 was conducted. All presented with acute-onset abdominal or flank pain. Clinical features, imaging studies, and laboratory findings served as grounds for diagnosis, having excluded more common conditions (ie, fibromuscular dysplasia, collagen vascular disorders, or arteritis). CT angiography was done initially and repeated periodically (Week 1, Month 3, then yearly). Treatment was conservative, utilizing endovascular intervention as warranted by CT diagnostics. In a related systematic review, all English literature from 1976 to 2015 was screened via the PubMed database, assessing patient demographics, affected arteries, clinical presentations, and treatment methods.

FINDINGS

Ultimately, 25 arterial lesions identified in eight patients (median age, 62.8 years; range, 40-84 years) were monitored for a median period of 26 months (range, 15-57 months). At baseline, celiac axis (3/8, 37.5%), superior mesenteric (4/8, 50%), and common hepatic (2/8, 25%) arteries were involved, in addition to isolated lesions of right renal, splenic, right colic, middle colic, gastroduodenal, left gastric, right gastroepiploic, proper hepatic, right hepatic, and left hepatic arteries. Compared with prior publications, celiac axis and superior mesenteric artery were more commonly affected in cohort. Arterial dissections (n = 8), aneurysms (n = 5), stenoses or occlusions (n = 4), and a single pseudoaneurysm were documented. Despite careful conservative management, new splanchnic arterial lesions (n = 4) arose during follow-up. Considering the few available reports of new arterial lesions in the literature, newly developing pathology is a distinctive feature of our patients, four of whom eventually required endovascular interventions.

CONCLUSIONS

Careful clinical observation via periodic CT angiography is required in patients with SAM, checking for newly developing lesions. The natural history of SAM should be clarified in a larger patient population.

Segmental arterial mediolysis: a systematic review of 85 cases

BACKGROUND

Segmental arterial mediolysis (SAM) is a nonatherosclerotic, noninflammatory arteriopathy of unknown etiology with life-threatening manifestations. With advances in endovascular techniques, SAM is increasingly being managed without the need for major surgery.

METHODS

A systematic review of the literature published on SAM between 1976 and 2012 was performed, focusing on arterial involvement, diagnostic imaging modalities, mortality and morbidity rates, and in particular treatment outcomes with open versus endovascular intervention.

RESULTS

Sixty-two studies reporting on 85 cases of SAM were reviewed. Sixty-nine percent of cases were diagnosed histologically (24% on autopsy). Angiography was the most common form of diagnostic imaging modality (56% of cases). Arterial involvement was largely abdominal or cranial, with splenic arterial involvement being the most prevalent (29% of cases). There was a total SAM-related mortality of 26%. Endovascular intervention, most commonly in the form of coil embolization of aneurysmal vessel(s), was successful in 88% of cases where attempted, with no reported mortality. There was a mortality rate of 9% where open surgery was attempted.

CONCLUSIONS

Catheter-based endovascular techniques can be a successful, minimally invasive treatment option in the management of this potentially life-threatening condition, and may also provide a temporary bailout measure in the acute phase before definitive surgical treatment at a later stage.

Pathomorphometry of ruptured intracranial vertebral arterial dissection: adventitial rupture, dilated lesion, intimal tear, and medial defect

OBJECT

Subarachnoid hemorrhage (SAH) due to ruptured intracranial vertebral artery (VA) dissection is a life-threatening disease. Angiographic and symptomatic prognostic factors for rupture and rerupture have been investigated, but the pathological characteristics have not been fully investigated. The authors aimed to investigate these features by performing a pathomorphometic study of ruptured intracranial VA dissections.

METHODS

This study included 50 administrative autopsy cases of fatal SAH due to ruptured intracranial VA dissection among 517 fatal nontraumatic cases of SAH occurring between March 2003 and May 2011. Pathomorphometry was performed using serial 5-μm histological cross-sections with elastica van Gieson staining from each 0.2-mm segment around the ruptured intracranial VA. The longitudinal lengths of 4 types of vascular lesions-adventitial ruptures, dilated lesions where the internal elastic lamina (IEL) was ruptured with adventitial extension, intimal tears where the IEL was ruptured, and medial defects-were calculated based on the numbers of the slides in which these lesions were continuously detected (minimum 2 adjoining slides). The distance from the vertebrobasilar junction to the center of adventitial rupture was also calculated in 37 cases.

RESULTS

All cases showed one adventitial rupture with a mean length of about 1.9±1.1 mm. The center of the adventitial rupture was located 5.0-26.8 mm (mean 14.6±5.5 mm) from the intracranial VA bifurcation. Adventitial ruptures existed in the centers of dilated lesions, where the adventitia was highly extended. Other vascular lesions were serially observed surrounding the adventitial rupture. The mean lengths of dilated lesions, intimal tears, and medial defects were 9.4±4.8 mm, 13.2±6.3 mm, and 15.6±7.2 mm, respectively. The lengths between proximal lesions and distal lesions from the center of the adventitial rupture for both medial defects and intimal tears were significantly longer at proximal lesions than at distal ones (chi-square test, p<0.01).

CONCLUSIONS

Every ruptured intracranial VA dissection has a single point of adventitial rupture where the adventitia was maximally extended, so dilation appears to be a valuable predictive factor for hemorrhagic intracranial VA dissections. The adventitial ruptures were as small as 2 mm in length, and clinically detectable dilated lesions were about 9 mm in length. However, vascular vulnerability caused by IEL ruptures and medial defects existed more widely across a length of VA of 1.3-1.5 cm. Comparatively broader protection of the intracranial VA than the clinically detected area of dissection might be desirable to prevent rebleeding. Broader protection of proximal lesions than distal lesions might be effective from the viewpoint of site distribution of vascular lesions and blood flow alteration to the pseudolumen caused by the dissecting hematoma. Medial defects are the most widely seen lesions among the 4 types of vascular lesions studied. Medial degenerative disease, known as segmental arterial mediolysis, is suspected in the pathogenesis of intracranial VA dissections.

Segmental arterial mediolysis accompanied by renal infarction and pancreatic enlargement: a case report

Introduction

Due to recent advances in imaging diagnostic techniques, there are an increasing number of case reports of segmental arterial mediolysis. However, there are only a limited number of reports on segmental arterial mediolysis-related abnormalities of abdominal organs other than the intestine. This report describes a case of segmental arterial mediolysis accompanied by abnormalities of abdominal organs without clinical symptoms.

Case presentation

A 52-year-old Japanese man with hematuria and no prior medical history was referred to a urologist and was diagnosed as having urinary bladder cancer. He underwent trans-urethral resection of the bladder tumor and intra-vesical instillation therapy, which was followed by observation. During follow-up, although no abdominal symptoms were observed, an abdominal computed tomography scan revealed a dissection of the superior mesenteric artery. A false lumen partially occluded by a thrombus was located distal to this occlusion. The lumen was irregularly shaped with narrow and wide sections. Similar irregularities were also observed in the wall of the inferior mesenteric artery. Arterial dissection with thromboembolism in the left renal artery and renal infarction was also observed. Follow-up computed tomography after two months revealed an enlargement of the pancreatic tail adjacent to the splenic artery. Follow-up three-dimensional computed tomography showed gradual re-expansion of the true lumen of the superior mesenteric artery, improvement in arterial wall irregularities, and a reduction in the pancreas enlargement and renal infarction. Over the following 15 months, these changes gradually normalized. On the basis of the vascular changes in multiple arterial systems that resolved spontaneously, we considered that the lesions were associated with segmental arterial mediolysis.

Conclusions

We present a rare case of segmental arterial mediolysis accompanied by abnormalities of abdominal organs without clinical symptoms. Three-dimensional computed tomography was useful for follow-up evaluation in our patient.

Subarachnoid hemorrhage in a case of segmental arterial mediolysis with coexisting intracranial and intraabdominal aneurysms

The authors report the rare case of a 58-year-old man with segmental arterial mediolysis (SAM) with associated intracranial and intraabdominal aneurysms, who suffered subarachnoid hemorrhage (SAH) due to rupture of an intracranial aneurysm. This disease primarily involves the intraabdominal arterial system, resulting in intraabdominal and retroperitoneal hemorrhage in most cases. The patient presented with severe headache and vomiting. The CT scans of the head revealed SAH. Cerebral angiography revealed 3 aneurysms: 1 in the right distal anterior cerebral artery (ACA), 1 in the distal portion of the A1 segment of the right ACA, and 1 in the left vertebral artery. The patient had a history of multiple intraabdominal aneurysms involving the splenic, gastroepiploic, gastroduodenal, and bilateral renal arteries. He underwent a right frontotemporal craniotomy and fibrin coating of the dissecting aneurysm in the distal portion of the A1 segment of the right ACA, which was the cause of the hemorrhage. Follow-up revealed no significant changes in the residual intracranial and intraabdominal aneurysms. An SAH due to SAM with associated multiple intraabdominal aneurysms is extremely rare. The authors describe their particular case and review the literature pertaining to SAM with associated intracranial and intraabdominal aneurysms.

Segmental arterial mediolysis: report of 2 cases and review of the literature

Segmental arterial mediolysis (SAM) is an idiopathic noninflammatory vasculopathy involving small to medium arteries, usually in the abdomen, although arteries in the cerebral and coronary circulations also may be affected. Some cases present as abdominal apoplexy due to aneurysmal rupture, but ischemia and infarction also occur. Not uncommonly, SAM may be misdiagnosed as a systemic necrotizing vasculitis. We present 2 patients with bilateral renal infarctions, cerebral arterial dissections, and visceral artery microaneurysms. Both were diagnosed initially as polyarteritis nodosa. The diagnosis was changed to SAM, in one case based on clinical and radiologic features, and in the other, on an open wedge kidney biopsy. We discuss the differential diagnosis and review the literature on SAM.

Differential diagnosis between traumatic and nontraumatic rupture of the intracranial vertebral artery in medicolegal autopsy

We attempted to establish histopathological identification between traumatic rupture and nontraumatic arterial dissection of the intracranial vertebral artery (IVA) resulting in subarachnoid hemorrhage (SAH). Step-serial observations of ruptured IVAs among four traumatic and 44 nontraumatic SAH patients were investigated. We found that the most specific characteristic for differentiation was the shape of the ruptured adventitia. Extension of the adventitia was clearly observed in nontraumatic cases. In contrast, traumatic cases showed transmural ruptures. Other specific characteristics were also detected. For traumatic cases, small incomplete tears of intima and media were frequently found; they formed oblique tears without adventitial extension. Fragmentized internal elastic lamina was also observed in traumatic cases. In contrast, previous arterial dissections were frequently confirmed in nontraumatic cases. Medial degenerations or defects were detected in all nontraumatic cases. In these cases, the peripheral lesion of the rupture was appeared as intimal tears at recessed vascular wall caused by medial defects. This suggested a relationship between medial lesions and pathogenesis of arterial dissections. These additional features were found in both ruptured and non-ruptured intracranial arteries. We concluded that histopathological investigation is a reliable method for differential diagnosis between traumatic and nontraumatic rupture of the IVA resulting in fatal SAH. These morphological differentiations could be valuable for medicolegal diagnosis.