INTRODUCTION
Cerebral aneurysms of more than 7 mm are considered at risk for rupture. The International Study of Unruptured Intracranial Aneurysms (ISUIA)-1 (1998) and ISUIA-2 (2003) suggested that there is a negligible risk of subarachnoid hemorrhage (SAH) in aneurysms more than 7 mm4,17). However, our experience is contrary to these studies and ruptures do occur in aneurysms smaller than 3 mm. In this paper, we analyzed 7 patients with spontaneous SAH ruptured cerebral aneurysms smaller than 3 mm.
MATERIALS AND METHODS
From January 2019 to June 2022, there were 530 patients treated for cerebral aneurysms as summarized in Table 1. Among them, there were 183 patients with ruptured cerebral aneurysms and 7 patients who were diagnosed with spontaneous SAH with ruptured saccular aneurysm smaller than 3 mm and treated with coil embolization. Gender, age, location, hypertension and smoking were checked for evaluation of risk factors and complications in radiology and clinical outcome after coil embolization for evaluation of treatment.
1. Case 1
A 60-year-old male patient presented to the emergency room with severe headache and decreased consciousness (Fig. 1). On arrival, he had a drowsy mentality and a Glasgow Coma Scale (GCS) score of 13. Brain computed tomography (CT) scan showed SAH of modified Fisher scale 3. On transfemoral cerebral angiography (TFCA), saccular aneurysm measuring 1.95 mm in neck and 2.35 mm in height was identified in the anterior communicating artery (ACoA) through TFCA, and emergency coil embolization was performed. He was discharged after showing improvement, and 6 months later, there was no abnormality including regrowth on the follow-up magnetic resonance angiography (MRA), and he is currently under observation.
2. Case 2
An 80-year-old female patient was brought to the emergency room complaining of decreased consciousness (Fig. 2). On arrival, she had drowsy mentality and a GCS of 13. Brain CT showed SAH of modified Fisher scale 4. TFCA revealed a saccular aneurysm measuring 2 mm in the neck and 2.51 mm in height with right middle cerebral artery (MCA) bifurcation, so coil embolization was performed as an emergency. Coil embolization was done successfully, and she was managed medically over the next month. She was discharged without any neurological abnormalities and a follow-up MRA 6 months later showed no abnormalities.
3. Case 3
A 78-year-old female patient presented to the emergency room complaining of severe headache (Fig. 3). She had suffered from severe headache since the morning of the day. She was alert at the time of her visit (GCS 14) and showed no neurological abnormalities. Brain CT showed SAH of modified Fisher scale 4. TFCA showed an aneurysm measuring 1.57 mm in neck and 2.51 mm in height from right posterior communicating artery. Coil embolization was performed as an emergency. She was discharged without any neurological symptoms other than intermittent headache. MRA for 1 year showed no specific findings.
4. Case 4
A 70-year-old female patient was found unconscious and was brought to emergency room (Fig. 4). At the time of her visit, she was confirmed to have a GCS score of 12 and a drowsy mentality. Brain CT is a massive SAH with an intraparenchymal hematoma in relation to an aneurysm. TFCA revealed a saccular aneurysm measuring 1.97 mm in the neck and 2.54 mm in height from ACoA, and coil embolization was performed as an emergency. Follow-up over a period of 1 year showed gradual neurological recovery with no focal deficits and some minor headaches. And MRA showed no specific findings.
5. Case 5
A 49-year-old female patient presented to the hospital complaining of temporal pain that had persisted for a week (Fig. 5). At the time of visit, she had an alert mentality and all neurological examinations were normal except for the headache. Brain CT revealed SAH of modified Fisher scale 3. TFCA revealed a saccular aneurysm measuring 1.92 mm in neck and 2.35 mm in height from the right MCA bifurcation. Emergency coil embolization was performed. The patient was discharged without any other sequelae, and 1-year follow-up MRA showed no specific findings.
6. Case 6
A 43-year-old female patient was brought to the emergency room in a state of decreased consciousness (Fig. 6). Upon arrival at the hospital, the patient had a stupor mentality and a GCS score of 6. She had a generalized tonic-clonic seizure once. Brain CT revealed SAH of modified Fisher scale 4. A saccular aneurysm measuring 1.39 mm in the neck and 3.02 mm in height was found in the left MCA (M1 segment) on TFCA, and coil embolization was performed as an emergency. The patient is still in the hospital after two months and is under full assisted care. She is able to breathe normally with a tracheostomy in place and nasogastric tube feeding, but unable to move her limbs or speak.
7. Case 7
A 71-year-old male patient was brought to the emergency room with a headache and nausea that suddenly developed while fishing (Fig. 7). He was alerted before his visit, but his consciousness gradually decreased, and at the time of his visit, he had a drowsy mentality and a GCS score of 13. A brain CT revealed a SAH of modified Fisher scale 4. A saccular aneurysm measuring 1.5 mm neck and 1.96 mm height was found in the right distal anterior cerebral artery (ACA) on TFCA. Coil embolization was performed as an emergency. The patient was discharged without neurological symptoms, and a 6-month follow-up MRA showed no unusual findings.
RESULTS
In period of 4 years, age range of 7 patients were 43 to 80 (5 females and 2 males) as summarized in Table 2. Saccular aneurysms were located in anterior and posterior circulation. The 4 patients were diagnosed with hypertension and 3 patients were smokers. Successful coil embolization with subtotal occlusion with remnant neck was done in 7 patients and there were no complications in radiologic findings and clinical outcomes in all patients.
DISCUSSION
It is known that the risk of cerebral aneurysm rupture increases depending on the size of the cerebral aneurysm10,17). However, many patients develop SAH due to rupture of small cerebral aneurysms less than 5 mm in size1,10,12). Especially, the risk of rupture of very small aneurysms <3 mm is somewhat underestimated. Morita et al.10) reported that the annual rupture rate of intracranial aneurysms less than 5 mm was 0.23% in MCA and 0.9% in ACA. And Ishibashi et al.5) reported that the annual rupture rate according to aneurysm size was 0.8% (< 5 mm), 1.2% (5-9.9 mm), 7.1% (≥ 10 mm), and 43.1% (≥ 25 mm), of which 6 cases were less than 3 mm. Chandra et al.3) reported approximately 1,200 cases of cerebral aneurysms 3 mm or less and found that the risk of rupture within 3.8 years was approximately 0.4% to 1.5%. This result is somewhat in contrast to the ISUIA report that the risk of rupture of small cerebral aneurysms 7 mm or less was negligible4,17). Risk factors for rupture of small brain aneurysms include age6), high blood pressure8,13), smoking6,8), being female7,13,16) and location of aneurysm7,13). This analysis also shows a similar trend in the seven cases presented in this paper.
Intraprocedural rupture is a representative complication that may occur during treatment14). van Rooij et al.15) reported on intraprocedural rupture rates based on 1,295 patients with aneurysms. In this study, surgical rupture of very small aneurysms occurred more frequently than in larger aneurysms (7.7% vs. 3.6%) and retreatment rate was lower (5.1% vs. 10.0%). Nguyen et al.11) reported that the intraprocedural rupture rate in ruptured very small cerebral aneurysms during endovascular treatment was five times higher than that of larger ruptured aneurysms. Advances in interventional materials and surgical techniques have reduced the intraprocedural rupture rate of endovascular treatment for very small cerebral aneurysms11). Yamaki et al.18) reported that the intraprocedural rate of endovascular treatment for very small cerebral aneurysm was 7%, which was lower than previously reported rates (8.3%)2,18).
Recurrence is a common complication that affects the patient's long-term prognosis. Zheng et al.20) reported 501 cases of intracranial aneurysms with endovascular treatment. Recurrence rate was 13.9% and the aneurysm retreatment rate was 3.5%. Larger size and initial incomplete occlusion were predictors of recanalization. Zhang et al.19) reported 92 patients with ruptured very small cerebral aneurysms using endovascular treatment, and the postoperative recurrence rate was 7.5%. Coiling without a stent was the only factor significantly associated with aneurysm recurrence. The stent prevents the coil from protruding into the parent vessel. Li et al.9) reported 162 cases of ruptured very small cerebral aneurysms with coil embolization or microsurgical clipping. In this report showed that age, Hunt-Hess grade, cerebral vasospasm, and perioperative complications were significantly associated with the clinical outcomes of patients no matter the treatment method adopted.
CONCLUSION
Very small aneurysms are considered to be somewhat safer than other cerebral aneurysms due to their size. However, there is a clear risk of rupture, and treatment is required considering the patient's risk factors. Ruptured aneurysms smaller than 3 mm could be treated with coil embolization and advantageous. And if a rupture of a very small aneurysm occurs, endovascular treatment is a safe and efficient approach.
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