□ CASE REPORT □

Partially Thrombosed Vertebral Artery Dissecting Aneurysm
Presenting as Delayed Bulbar Compression after Lateral
Medullary Infarction
Yuji Kato 1, Fumitaka Yamane 2, Takeshi Hayashi 1, Shinya Kohyama 2, Shoichiro Ishihara 2,
Akira Uchino 3 and Norio Tanahashi 1

Abstract
A 48-year-old man experienced lateral medullary infarction resulting from spontaneous vertebral artery
(VA) dissection. Minimal fusiform dilatation was noted on basi-parallel anatomic scanning-magnetic resonance imaging; therefore, the patient was treated conservatively. Eight months later, he experienced deterioration of dysphagia and the onset of gait ataxia. Repeated imaging studies showed enlargement of the VA aneurysm with bulbar compression. Parent artery occlusion on the proximal side of the VA affected by the dissection relieved the patient’s symptoms. Although the majority of dissected lesions stabilize within a few
months, studies with longer observation periods and more frequent neuroimaging examinations are required.
Key words: vertebral artery dissecting aneurysm, lateral medullary infarction, medulla oblongata
compression, basi-parallel anatomic scanning
(Intern Med 54: 427-429, 2015)
(DOI: 10.2169/internalmedicine.54.3347)

Introduction
Partially thrombosed vertebral artery (VA) aneurysms tend
to become very large and thus induce symptoms of brainstem compression. However, symptomatic bulbar compression by VA aneurysms is rare, with only a few cases having
been reported (1-4). Furthermore, to our knowledge, there
are no previous cases of delayed bulbar compression due to
a slowly growing VA dissecting aneurysm following lateral
medullary infarction. We herein report a case of a VA dissecting aneurysm successfully treated with parent artery occlusion (PAO).

Case Report
A healthy 48-year-old man noticed left-side neck tenderness. Five days later, he experienced numbness of the right
hand with vertigo and dysarthria. He was admitted to our

hospital, where the initial neurological examination findings
were suggestive of Wallenberg syndrome. Diffusionweighted magnetic resonance (MR) imaging performed on
admission showed acute infarction in the left posterolateral
medulla (Fig. 1A), and MR angiography indicated an indistinct flow in the left VA (Fig. 1B). Meanwhile, basi-parallel
anatomic scanning (BPAS)-MR imaging (5) performed on
day 6 showed fusiform dilatation of the outer contour at the
narrowing portion of the left VA (Fig. 1C), with the source
MR angiographic image showing a double lumen in the left
VA (Fig. 1D). These findings were indicative of VA dissection. The patient was treated conservatively without antiplatelet therapy, as the MR and BPAS-MR imaging findings
on day 27 indicated a stable size and morphology. The patient was subsequently discharged on day 34 and resumed a
normal lifestyle after six months of rehabilitation.
Eight months after the initial medullary infarction, the patient experienced deterioration of dysphagia and the onset of
gait ataxia. His blood pressure remained well controlled (<

１

Department of Neurology and Cerebrovascular Medicine, Saitama International Medical Center, Saitama Medical University, Japan, ２Department of Endovascular Neurosurgery, Saitama International Medical Center, Saitama Medical University, Japan and ３Department of Diagnostic
Radiology, Saitama International Medical Center, Saitama Medical University, Japan
Received for publication May 26, 2014; Accepted for publication July 9, 2014
Correspondence to Dr. Yuji Kato, yujik@saitama-med.ac.jp

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Intern Med 54: 427-429, 2015

DOI: 10.2169/internalmedicine.54.3347

Figure 1. A: Diffusion-weighted MR image obtained on admission showing a high-intensity lesion
in the left posterolateral medulla oblongata. B: MR angiography image showing an indistinct flow in
the left VA (arrow). C: BPAS-MR image obtained on day 6 showing fusiform dilatation of the outer
contour in the narrowed segment of the left VA (arrows). D: MR angiographic source image revealing
the double lumen in the left VA (arrow). E: T2-weighted MR image obtained eight months after onset
showing a heterogeneous mass associated with a low-intensity signal rim (10 mm in diameter) compressing the medulla oblongata adjacent to the left anterior side, suggestive of a partially thrombosed
VA aneurysm (arrowheads). F: MR angiography image showing narrowing of the left VA. G: BPASMR image demonstrating obvious growth of the aneurysm. H: T2-weighted MR image obtained six
months after PAO showing a decrease in the size of the aneurysm (arrowheads). MR: magnetic resonance, BPAS-MR: basi-parallel anatomic scanning-MR, VA: vertebral artery

140/90 mmHg) with imidapril during this period. T2weighted MR imaging suggested enlargement of the partially thrombosed VA aneurysm compressing the medulla
from the left anterior side (Fig. 1E). Although the findings
of MR angiography showed narrowing of the left VA
(Fig. 1F), BPAS-MR imaging performed at that time demonstrated significant aneurysmal enlargement at the site of
VA dissection (Fig. 1G). Due to growth of the lesion and
deterioration of the patient’s neurological symptom, we performed PAO at the proximal region of dissection in order to
preserve the perforators from the aneurysmal dome. A partially thrombosed aneurysm was successfully occluded using
platinum coils (Fig. 2). Thereafter, the patient’s clinical
symptoms gradually improved, and MR imaging, including

BPAS, performed six months after the procedure revealed a
decrease in the size of the aneurysm (Fig. 1H).

Discussion
It remains unclear how long dynamic changes in dissecting aneurysms persist after symptom onset. Studies have indicated that aneurysm enlargement is observed only in the
relatively early phase, at three weeks in most cases (6, 7).
Furthermore, the degree of fusiform dilation usually remains
unchanged, even resolving in some patients (7). The course
of the present case, on the other hand, was not in line with
that of previous reports. It is not possible to precisely determine how long the lesion should be monitored based on the

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Intern Med 54: 427-429, 2015

DOI: 10.2169/internalmedicine.54.3347

Figure 2. A: Preoperative left VA angiogram showing the aneurysm. B: Radiograph revealing the
shape of the coil mass packed into the aneurysm. C: Postoperative left VA angiogram showing complete obliteration of the aneurysm. D: Postoperative right VA angiogram showing retrograde filling
to the distal end of the left VA. VA: vertebral artery

first angiographic manifestations. Although the majority of
dissected lesions stabilize within a few months (7), a longer
observation period and more frequent neuroimaging studies
may be required in some cases.
The pathogenesis of aneurysms growth remains poorly
elucidated. The proposed mechanism accounting for the
slow growth of VA aneurysms involves the “two-stage dissection theory,” in which the initial insult is macroscopic arterial dissection, a process later coupled with the development of multiple sites of mural microdissection secondarily
to underlying weakness of the internal elastic lamina (8). In
the present case, thrombus formation at the false lumen may
have resulted in parent artery narrowing as well as the formation of the mass causing bulbar compression. We confirmed the patient’s vascular condition using noninvasive
BPAS-MR imaging (5), which can be employed to detect
the outer contour of aneurysms even if the VA is occluded.
Because aneurysms can grow even after the occurrence of
complete thrombotic changes (2), providing careful followup, including BPAS-MR imaging, is necessary.
In summary, we herein reported a case of a partially
thrombosed VA aneurysm compressing the medulla oblongata. Slow growth of the aneurysm after lateral medullary
infarction may cause symptoms owing to bulbar compression. The administration of endovascular treatment, such as
PAO, should be considered as soon as possible in cases of
unruptured VA dissection associated with growing aneurysmal dilation during the follow-up period.

The authors state that they have no Conflict of Interest (COI).

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Ⓒ 2015 The Japanese Society of Internal Medicine
http://www.naika.or.jp/imonline/index.html

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