| Home | E-Submission | Sitemap | Editorial Office |  
Journal of Korean Neurosurgical Society > Volume 55(5); 2014 > Article
Kim, Kim, Kim, and Kang: Thrombosis and Recanalization of Small Saccular Cerebral Aneurysm : Two Case Reports and a Suggestion for Possible Mechanism


Reports of thrombosis and recanalization of cerebral aneurysm are rare. We report two cases of small, saccular aneurysms in which spontaneous thrombosis had occurred during the preparation for endovascular coiling. Also, we review reported cases and propose the presumed pathogenesis.


The incidence of spontaneous thrombosis of cerebral aneurysm is about 1-2% of ruptured aneurysms7). Spontaneous thrombosis of cerebral aneurysm is considered as a hemodynamically unstable status, and the natural history of giant or large aneurysm has been suggested (growth, recanalization, and even rupture or thromboembolic event)3,5,6,16). However, the reports on recanalization of small aneurysm after spontaneous thrombosis are rare, and the natural history is still unknown.
We present two cases of spontaneous thrombosis and recanalization of small saccular aneurysms, and suggest a presumed mechanism, and its clinical significance23).


Case 1

A 52-year-old woman presented to the emergency room with a sudden-onset stuporous mentality. The medical history was significant for hypertension and diabetes, for which the patient was taking oral medications. In addition, the patient was suffering from angina, and was taking 100 mg of aspirin daily.
Brain computed tomographic (CT) scans revealed a subarachnoid hemorrhage (SAH) at the basal cistern and both sylvian fissures, mainly on the left side. Three-dimensional (3D) CT reconstruction revealed an aneurysm at the basilar bifurcation and at left anterior choroidal artery. The basilar bifurcation aneurysm was 10×10 mm in size, with a broad neck (9 mm). The left anterior choroidal artery aneurysm was 3×6 mm in size, with an irregular shape (Fig. 1A). Based on the distribution of the hematoma and the shaped of aneurysms, we considered the left anterior choroidal artery aneurysm to be ruptured and decided to perform an emergency endovascular coil embolization on the day of admission.
Under general anesthesia, we performed induced hypotension below 60 mm Hg of mean arterial pressure. Baseline cerebral angiography revealed that the left anterior choroidal artery aneurysm had decreased in size compared to that found in the 3D angiography (Fig. 1B, C). Additionally, we could not observe contrast filling from the distal part of the aneurysm. Because partial occlusion of the aneurysm might increase the risk of rebleeding after thrombolysis, we decided not to perform coil embolization14). Also, given the patient's conditions (aspirin medication and pulmonary edema combined with pneumonia), we could not perform aneurysm clipping at early stage.
Follow-up angiography 7 days later demonstrated complete recanalization of the distal part of the aneurysm (Fig. 1D, E). Accordingly, we performed surgical clipping, and the patient recovered and was discharged with a Glasgow outcome scale (GOS) score of 5.

Case 2

A 58-year-old man was admitted to our neurosurgical department for the evaluation of headache and dizziness that occurred several months earlier. The patient's past medical history was unremarkable. On admission, the patient had no neurological signs or abnormal hematological findings including coagulation time.
Brain 3D CT angiography revealed a 3×1.7 mm aneurysm in the basilar bifurcation, and a 3×1.5 mm aneurysm in the proximal middle cerebral artery (MCA). We decided to perform endovascular coil embolization with consent from family members.
Under general anesthesia, we performed endovascular coiling. Baseline angiography revealed small aneurysm in the proximal MCA (Fig. 2A). We placed a guiding catheter into the proximal internal cerebral artery, and the microcatheter was placed in the proximal MCA. Subsequent road map and angiography revealed complete disappearance of the right MCA aneurysm without evidence of vasospasm (Fig. 2B). Therefore, we only performed a coil embolization of the basilar bifurcation aneurysm.
The follow-up angiography 48 days later confirmed complete recanalization of the right MCA aneurysm (Fig. 2C). We performed coil embolization without any complications.


Several mechanisms have been reported to contribute to spontaneous thrombosis of cerebral aneurysms. We show a summary of reported cases of spontaneous thrombosis (Table 1). It is well known that spontaneous thrombosis in giant or large aneurysm is related to the ratio of aneurysm volume to neck size, as have been demonstrated in an animal model of aneurysm1). The blood flow within giant or large aneurysms is slow and turbulent, which may induce spontaneous thrombosis3).
However, hemodynamic or local factors seem to be more important in spontaneous thrombosis of small aneurysms. Spetzler et al.20) reported a case of small aneurysm that disappeared and reappeared. They did refer to the possible effect of anti-fibrinolytic agent or vasospasm. The angiographic procedure itself has been also proposed. Non-ionic contrast media has been reported to have thrombogenic potential8). Systemic hypotension was postulated as a potential mechanism for spontaneous thrombosis2). Nakajima et al.17) suggested aneurysmal shape and the surrounding clot as putative factors related to the intermittent appearance of the aneurysm.
In this report, we were uncertain as to the mechanism of spontaneous thrombosis in these small aneurysms, but have considered two possibilities. Induced hypotension under general anesthesia might have played some role in the spontaneous thrombosis. We usually adopt systemic hypotension (mean arterial pressure below 60 mm Hg) after the induction of general anesthesia in the patient with ruptured intracranial aneurysm. We presumed that sudden decrease of blood pressure might result in circulatory delay and spontaneous thrombosis of ruptured aneurysm under increased intracranial pressure. Bohmfalk and Stroy2) postulated systemic hypotension as a possible mechanism for angiographic disappearance of aneurysm. The other was the result of blood flow stagnation from the microcatheter during endovascular procedure. In case 2, spontaneous thrombosis occurred before the selection of the aneurysm by microcatheter and microguidewire. Also, there was no angiographic evidence of vasospasm. Accordingly, we presumed that blood flow stagnation due to the microcatheter caused spontaneous thrombosis in small aneurysm. Szajner et al.22) suggested vasospasm in addition to flow arrest from microcatheter and microguidewire during coli embolization as a possible etiology of spontaneous thrombosis in small aneurysms.
In summary, spontaneous thrombosis in ruptured small saccular aneurysms may attribute to anti-fibrinolytic agent, vasospasm, systemic hypotension, surrounding clot, and contrast media. The contrast media and blood flow stagnation may be possible etiologies in unruptured cases. Especially, spontaneous thrombosis of ruptured small aneurysms may occur during the early period after SAH and could be recanalized within the next few weeks9,17).


Spontaneous thrombosis of small saccular aneurysm is attriuted to a number of factors. Induced hypotension and endovascular instruments may play a role in the occurrence of spontaneous thrombosis in small aneurysm.


1. Black SP, German WJ : Observations on the relationship between the volume and the size of the orifice of experimental aneurysms. J Neurosurg 17 : 984-990, 1960
crossref pmid
2. Bohmfalk GL, Story JL : Intermittent appearance of a ruptured cerebral aneurysm on sequential angiograms. Case report. J Neurosurg 52 : 263-265, 1980
crossref pmid
3. Brownlee RD, Tranmer BI, Sevick RJ, Karmy G, Curry BJ : Spontaneous thrombosis of an unruptured anterior communicating artery aneurysm. An unusual cause of ischemic stroke. Stroke 26 : 1945-1949, 1995
crossref pmid
4. Choi CY, Han SR, Yee GT, Lee CH : Spontaneous regression of an unruptured and non-giant intracranial aneurysm. J Korean Neurosurg Soc 52 : 243-245, 2012
crossref pmid pmc
5. Cohen JE, Itshayek E, Gomori JM, Grigoriadis S, Raphaeli G, Spektor S, et al : Spontaneous thrombosis of cerebral aneurysms presenting with ischemic stroke. J Neurol Sci 254 : 95-98, 2007
crossref pmid
6. Cohen JE, Rajz G, Umansky F, Spektor S : Thrombosis and recanalization of symptomatic nongiant saccular aneurysm. Neurol Res 25 : 857-859, 2003
crossref pmid
7. Edner G, Forster DM, Steiner L, Bergvall U : Spontaneous healing of intracranial aneurysms after subarachnoid hemorrhage. Case report. J Neurosurg 48 : 450-454, 1978
crossref pmid
8. Fareed J, Walenga JM, Saravia GE, Moncada RM : Thrombogenic potential of nonionic contrast media? Radiology 174 : 321-325, 1990
crossref pmid
9. Greenberg E, Janardhan V, Katz JM, Riina H, Zimmerman R, Gobin YP : Disappearance and reappearance of a cerebral aneurysm : a case report. Surg Neurol 67 : 186-188; discussion 188-189, 2007
crossref pmid
10. Hamilton MG, Dold ON : Spontaneous disappearance of an intracranial aneurysm after subarachnoid hemorrhage. Can J Neurol Sci 19 : 389-391, 1992
crossref pmid
11. Hans FJ, Krings T, Reinges MH, Mull M : Spontaneous regression of two supraophthalmic internal cerebral artery aneurysms following flow pattern alteration. Neuroradiology 46 : 469-473, 2004
crossref pmid
12. Hassan F, Taschner CA, Thines L, Lejeune JP, Pruvo JP, Leclerc X : Spontaneous thrombosis of a recurrent clipped intracranial aneurysm. J Neuroradiol 36 : 153-157, 2009
crossref pmid
13. Jayakumar PN, Ravishankar S, Balasubramaya KS, Chavan R, Goyal G : Disappearing saccular intracranial aneurysms : do they really disappear? Interv Neuroradiol 13 : 247-254, 2007
crossref pmid pmc
14. Johnston SC, Dowd CF, Higashida RT, Lawton MT, Duckwiler GR, Gress DR, et al : Predictors of rehemorrhage after treatment of ruptured intracranial aneurysms : the Cerebral Aneurysm Rerupture After Treatment (CARAT) study. Stroke 39 : 120-125, 2008
crossref pmid
15. Kim BJ, Kim JS, Jeon KD, Lee SI : Spontaneous complete occlusion of middle cerebral artery aneurysm : case report. J Cerebrovasc Endovasc Neurosurg 14 : 309-314, 2012
crossref pmid pmc
16. Lee KC, Joo JY, Lee KS, Shin YS : Recanalization of completely thrombosed giant aneurysm : case report. Surg Neurol 51 : 94-98, 1999
crossref pmid
17. Nakajima Y, Yoshimine T, Mori H, Nakamuta K, Fujimura I, Sakashita K, et al : Spontaneous disappearance and reappearance of a ruptured cerebral aneurysm : one case found in a group of 33 consecutive patients with subarachnoid hemorrhage who underwent repeat angiography. Neurol Res 22 : 583-587, 2000
crossref pmid
18. Nakau H, Nagatani H, Nakau R, Ametani T : Acute disappearance of ruptured aneurysm located near the origin of the superior cerebellar artery - case report -. Neurol Med Chir (Tokyo) 47 : 468-470, 2007
crossref pmid
19. Ohta H, Sakai N, Nagata I, Sakai H, Shindo A, Kikuchi H : Spontaneous total thrombosis of distal superior cerebellar artery aneurysm. Acta Neurochir (Wien) 143 : 837-842; discussion 842-843, 2001
crossref pmid
20. Spetzler RF, Winestock D, Newton HT, Boldrey EB : Disappearance and reappearance of cerebral aneurysm in serial arteriograms. Case report. J Neurosurg 41 : 508-510, 1974
crossref pmid
21. Su TM, Hsu SW, Chen WF, Lee TC, Cheng CH : Acute thrombosis and recanalization of a ruptured anterior communicating artery aneurysm. J Clin Neurosci 16 : 1077-1079, 2009
crossref pmid
22. Szajner M, Jargiello T, Trojanowski T, Szczerbo-Trojanowska M : Spontaneous thrombosis of the pseudoaneurysm of right SCA after an attempt at embolisation. A case report. Interv Neuroradiol 8 : 205-208, 2002
crossref pmid pmc
23. Wiebers DO, Whisnant JP, Huston J 3rd, Meissner I, Brown RD Jr, Piepgras DG, et al : Unruptured intracranial aneurysms : natural history, clinical outcome, and risks of surgical and endovascular treatment. Lancet 362 : 103-110, 2003
crossref pmid
Fig. 1
Brain 3-dimensional computed tomographic scan (A) reveals left anterior choroidal artery aneurysm, 3×6 mm in size (white arrow). Rotational angiography (B) and left lateral internal carotid artery angiography (C) shows a partial thrombosis of the distal part of the aneurysm (black and white arrow) compared to the findings of previous angiography. Follow up angiography (D and E) 7 days later demonstrates recanalization of the thrombosed aneurysm (black and white arrow).
Fig. 2
Cerebral angiography (A) reveals proximal middle cerebral artery aneurysm, 3×1.5 mm in size (black arrow). Subsequent angiography (B) shows complete disappearance of the aneurysm (black arrow). Follow up angiography (C) seven weeks later demonstrates complete recanalization of the aneurysm (black arrow).
Table 1
Presumed mechanisms of spontaneous thrombosis of cerebral aneurysms in published reports

ACA : anterior cerebral artery, A-com : anterior communicating, SCA : superior cerebellar artery, MCA : middle cerebral artery, ICA : internal carotid artery, PICA : posteroinferior cerebellar artery, P-com : posterior communicating, R : ruptured, UR : unruptured, Acho : anterior choroidal

PDF Links  PDF Links
PubReader  PubReader
ePub Link  ePub Link
Full text via DOI  Full text via DOI
Download Citation  Download Citation
CrossRef TDM  CrossRef TDM
Related article
Editorial Office
#402, 27 Chilparo, Jung-gu, Seoul 04511, Korea
TEL: +82-2-525-7552   FAX: +82-2-525-7554   E-mail: kns61@neurosurgery.or.kr
About |  Browse Articles |  Current Issue |  For Authors and Reviewers
Copyright © Korean Neurosurgical Society. All rights reserved.                 developed in m2community
Close layer
prev next