Abstract

Background: Segmental arterial mediolysis (SAM) is a condition in which an aneurysm is formed by causing lysis of the media and remodeling of blood vessels. Short-term recurrence has been reported in abdominal aortic aneurysms. Cerebral aneurysms have been suggested to form in a short period not only in the abdominal cavity but also in the intracranial arteries in SAM.

Case Description: A 36-year-old pregnant woman at 35 weeks’ gestation developed sudden headache and disorientation. Head magnetic resonance imaging showed a small amount of subarachnoid hemorrhage in the right ambient cistern. A fusiform cerebral aneurysm was found in the periphery of the right superior cerebellar artery, and small saccular aneurysms were found in the periphery of the right posterior cerebral artery and left posterior inferior cerebral artery. After delivery of the fetus, endovascular embolization of the ruptured aneurysm was performed. However, 10-week postoperatively, she developed sudden headache. Hemorrhage was found in the fourth ventricle, and enlargement of the left posterior inferior cerebellar artery (PICA) peripheral aneurysm and disappearance of the right posterior cerebral artery peripheral aneurysm were confirmed. A ruptured aneurysm in the peripheral left PICA was removed after trapping. Intraoperatively, an unruptured thrombosed aneurysm that was not visualized by imaging was also removed. Histopathological examination showed no calcification or inflammation, rupture of the internal elastic lamina, and lack of segmentation, and SAM was diagnosed.

Conclusion: In atypical dissecting aneurysms, SAM should be considered as a differential diagnosis. Systemic examination and short-term follow-up are also necessary.

Keywords: Dissecting aneurysm, Segmental arterial mediolysis, Subarachnoid hemorrhage

INTRODUCTION

Segmental arterial mediolysis (SAM) is a pathological condition in which the arterial wall becomes vulnerable due to degeneration of the arterial tunica media, resulting in arterial dissection and aneurysm formation. SAM is a pathological condition proposed by Salvin et al. in 1976 and was the first vascular lesion reported by Inayama et al. in 1992 in Japan. SAM is often reported as the cause of intra-abdominal hemorrhage due to a ruptured abdominal aneurysm. However, there are also reports of complications of subarachnoid hemorrhage (SAH) and intra-abdominal hemorrhage, and rarely, intracranial blood vessels alone.

In this report, we present a case of multiple cerebral aneurysms forming only in intracranial blood vessels, followed by an enlargement, a rupture, or disappearance of aneurysms in a short period. Pathological findings of some of the aneurysms resulted in a definitive diagnosis of SAM.

CASE REPORT

Clinical history

Case: A 36-year-old female

Imaging findings

Since the patient was pregnant, magnetic resonance imaging (MRI) was given priority, considering radiation exposure. A SAH was suspected because low signal intensity on the right ambient cistern on T2 star-weighted images and high signal intensity on fluid-attenuated inversion recovery images were observed [ Figures 1a and b ]. Although the patient was pregnant, a thorough examination was necessary. After shielding, a simple computed tomography (CT) scan of the head showed a faint, hyperabsorbed right bypass basin, and a 3D-CT scan showed a fusiform enlargement in the peripheral right superior cerebellar artery (SCA). The diagnosis was SAH due to a ruptured dissecting cerebellar aneurysm. In addition, small saccular aneurysms were also found in the periphery of the right posterior inferior cerebellar artery (PICA), which were diagnosed as unruptured cerebral aneurysms based on the distribution of hemorrhage [ Figures 1c and d ].

Figure 1:

(a) Fluid-attenuated inversion recovery image demonstrates hemorrhage in the right ambient cistern (red arrow head). (b) T2 star-weighted MR image demonstrates hemorrhage in the right ambient cistern (red arrow head). (c) Axial CT image demonstrates hemorrhage in the right ambient cistern (red arrow head). (d) CT angiography shows a dissecting cerebral aneurysm at the right distal SCA (red arrow head).

Progress (1)

In consultation with the obstetrics and gynecology department, it was decided to treat the aneurysm after delivery of the baby by cesarean section on day 2. The aneurysm was a deep lesion, requiring bypass and wrapping for craniotomy, which was considered highly risky. Therefore, endovascular treatment was performed. Embolization of the aneurysm from the main trunk of the SCA was performed using n-butyl cyanoacrylate since it was difficult to guide the catheter to the aneurysm site [ Figure 2 ]. Postoperative MRI revealed cerebral infarction in the right SCA region. Her consciousness was almost clear, with spelling aphasia and upper limb ataxia, and she was transferred to the hospital for rehabilitation with a modified Rankin scale score of 4.

Figure 2:

(a) Digital subtraction angiography examination of the vertebral artery angiogram shows a dissecting cerebral aneurysm at the right distal SCA (red arrow head), (b) which are occluded with n-butyl-2-cyanoacrylate (red arrow head).

Progress (2)

Ten weeks after the transfer, the patient developed sudden headache during rehabilitation. Head CT showed bleeding in the fourth ventricle and she was readmitted to the hospital. The 3D-CT angiography showed an enlargement of the previously observed aneurysm in the periphery of the right PICA, which was considered to be the bleeding source because it coincided with the bleeding site. Other aneurysms also showed changes in a short period (e.g., the disappearance of the peripheral aneurysm) [ Figure 3 ].

Figure 3:

(a) Axial CT image demonstrates hemorrhage in the right ambient cistern and fourth ventricle 10 weeks after the patient was transferred. (b-d) CT angiography showing a new aneurysm at the right distal PICA (red arrow head) and a disappearance of the peripheral aneurysm (red arrow).

Surgical findings

Direct surgery was performed for the peripheral right PICA aneurysm. Bilateral occipital subcranial craniotomy was performed in the prone position, the right PICA was traced to the periphery, and the aneurysm in the fourth ventricle was trapped and removed with the telovelotonsillar segment [ Figure 4 ]. A thrombotic unruptured aneurysm that was not visualized by 3D-CT angiography was also found in the right cerebellar hemisphere and thus was removed by trapping.

Figure 4:

Intraoperative findings show an aneurysm in the fourth ventricle in addition to the right distal PICA aneurysm (blue arrow). Both were trapped and removed. A thrombotic unruptured aneurysm on the right cerebellar hemisphere (blue arrow head) that was not visualized by 3D-CT was also removed.

Histopathological findings

Histopathological examination by Elastica van Gieson staining revealed that the internal elastic lamina was torn in the ruptured aneurysm and segmentally missing even in the unruptured aneurysm. On the other hand, no calcification of the blood vessel wall or infiltration of inflammatory cells was observed, and the patient was pathologically diagnosed with SAM [ Figure 5 ].

Figure 5:

In the ruptured aneurysm, the internal elastic lamina is segmentally torn. (a) Histopathological examination. (b) Elastica van Gieson. Even in an unruptured aneurysm, the internal elastic plate is segmentally missing. (c) Histopathological examination. (d) Elastica van Gieson. (e) Masson trichrome.

Postoperative course

Postoperative examination showed no obvious exacerbation of symptoms compared to preoperative examination; however, JCS I-1 and scanning speech remained. Since the pathological diagnosis was SAM, a CT scan and renal artery echo were performed to examine the abdominal cavity, but no obvious intra-abdominal aneurysm was noted. In addition, blood tests were negative for various antinuclear antibodies, and vasculitis workup was negative. She was transferred to the hospital and rehabilitation was continued.

DISCUSSION

In this case, a ruptured and an unruptured aneurysm were removed by surgery, and the pathological diagnosis led to a definitive diagnosis of SAM. As no abdominal aneurysm was found on whole-body CT, this is a very rare case that involved only the intracranial vessels.

SAM is a noninflammatory aneurysm without calcification, and a similar disease is fibromuscular dysplasia (FMD), which is a noninflammatory and nonarteriosclerotic arterial disease. The characteristic imaging findings of FMD include the string-of-beads sign;[ 1 ] however, SAM may also show similar findings[ 10 ] and cannot be distinguished by imaging. As for the clinical characteristics, SAM does not have a specific predominant age and sex group, whereas FMD is more common in young to middle-aged and female patients.[ 16 ] In addition, SAM has a high risk of aneurysm formation, rupture, and arterial dissection, and there is a risk of developing acute abdomen due to intra-abdominal aneurysm rupture, whereas stenosis and dissection lesions are seen in FMD, but the risk of bleeding is low.[ 10 ] Since treatment strategies differ between SAM and FMD due to the different risks, it is important to distinguish between the two conditions in determining the treatment approach.[ 10 ] Both diseases are differentially diagnosed by histopathological examination only when direct surgery can be performed.[ 10 ] However, since pathological diagnosis cannot be made in all cases, SAM may be diagnosed only by diagnostic imaging or clinical findings.[ 11 ]

FMD is histopathologically characterized by thickening or thinning of the blood vessel wall due to hyperplasia or the disappearance of smooth muscle and fibers.[ 23 ] The pathological findings of SAM are characterized by vacuolar degeneration of smooth muscle cells in the tunica media, which progresses to dissection of the tunica media from the adventitia, and formation of an aneurysm, resulting in the appearance of medial islands of residual tunica media in the arterial wall.[ 14 ] One of the characteristics is that there is no inflammation of the blood vessel wall or findings of porridge effect.[ 7 , 9 ] SAM easily forms an aneurysm in the intra-abdominal artery by remodeling, which was proposed by Salvin et al. in 1976 and first reported by Inayama et al. in 1992 in Japan. SAM has been often reported as intra-abdominal hemorrhage due to the rupture of an abdominal aneurysm, but less frequently, intracranial aneurysms have also been reported with pathological findings similar to those of the intra-abdominal aneurysms.[ 11 ] In the literature search, there were 17 reports of SAM cases that developed SAH [ Table 1 ].[ 2 - 6 , 8 , 11 - 13 , 15 , 17 , 19 - 22 ] Since 12 of 17 (71%) patients had intra-abdominal hemorrhage, close examination of the abdominal cavity is always recommended when diagnosing SAM-related subarachnoid hemorrhage. In the previous case reports, aneurysm formation due to rapid remodeling after aneurysm treatment has been reported in cases of abdominal aortic aneurysms caused by SAM.[ 14 , 19 ]

Table 1:

17 reports of SAM cases that developed SAH.

There are two notable points in this case report. First, in the intracranial artery, the known unruptured aneurysm enlarged and ruptured within a short period after the dissociative aneurysm ruptured. It is considered that this is related to the pathological condition of remodeling and changes in the blood vessel wall could be confirmed by pathological examination. The other point is that the aneurysm that was not detected by preoperative 3D-CT angiography was identified intraoperatively. The reason why the aneurysm could not be identified on imaging was thought to be because the inside of the aneurysm was completely thrombosed. The unruptured aneurysm found in the periphery of the right posterior cerebral artery disappeared on the images at the time of readmission, which may be due to the thrombus in the aneurysm. In cases where SAM cannot be completely ruled out, such as multiple cerebral aneurysms with dynamic changes in imaging findings or an atypical course for arterial dissection, closer follow-up of intracranial aneurysms may be required, even after the aneurysm treatment.

In this case, endovascular treatment was chosen because of the high risk of craniotomy due to the presence of a deep aneurysm. Depending on the choice of treatment, pathological diagnosis may not be possible, as in this case, but SAM should also be considered in the differential diagnosis when dynamic changes of atypical dissecting aneurysms or multiple cerebral aneurysms are observed. If new aneurysms or the enlargement of existing aneurysms are detected, early surgery may be necessary. On the other hand, in case studies of long-term follow-up of SAM, it has been reported that once the active phase is over, aneurysms no longer form.[ 18 ] Therefore, the literature recommends imaging follow-up every 6 months–1 year if aneurysms cannot be confirmed after 1 year of close follow-up.

CONCLUSION

In this study, we report a case with multiple coexisting aneurysms that changed in a short period after SAH due to the rupture of a dissecting aneurysm, and one of the aneurysms ruptured again. Histopathological examination confirmed SAM diagnosis. SAM is a disease that causes aneurysms to form in a short period due to vascular remodeling. When a noninflammatory aneurysm without calcification is observed on imaging, as in this case, SAM should be considered in the differential diagnosis for further investigation. Pathological diagnosis is necessary for definitive diagnosis, but it is necessary to consider detailed imaging follow-up even in the absence of pathological tissue confirmation.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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