Therapeutic dilemmas regarding giant aneurysms of the intracranial vertebral artery causing medulla oblongata compression

Abstract

Background

Giant aneurysms of the intracranial vertebral artery are very rare cerebrovascular lesions. Due to the rarity of these aneurysms, we know little about them.

Methods

We performed a systematic review of the English literature by searching the PubMed database. The inclusion criteria were as follows: (a) the full text was available and (b) complete clinical data were available.

Results

A total of 45 articles were identified, containing 53 patients (53 aneurysms). The patients were aged from 5 to 77 years (48.8 ± 20.8 years). Four patients receiving conservative treatment died. The remaining 49 patients were divided into the aneurysm removal group (n = 17) and the aneurysm reserve group (n = 32). The outcomes of the 49 treated cases could be obtained in 45 cases, 31 of which (68.9%, 31/45) had a Glasgow outcome scale score of 4–5.

Conclusions

It is still difficult to treat intracranial giant vertebral artery aneurysms, regardless of the treatment selected. Because of the malignant natural history, aggressive treatment is still advocated.

Introduction

Giant aneurysms of the intracranial vertebral artery (VA) are very rare. If left untreated, the aneurysms will gradually grow and compress the medulla oblongata, resulting in a poor prognosis. ¹ Especially for those ruptured, the prognosis is poor. Therefore, giant aneurysms of the intracranial VA need to be treated, and the treatments include open surgery and endovascular treatment (EVT).^2,3

Theoretically, microsurgical clipping with the combination of aneurysmectomy could relieve the mass effect of the giant aneurysm on the medulla oblongata. However, the surgical risk is extremely high. Although EVT is easy to conduct, it cannot relieve the mass effect. Moreover, intra-aneurysmal thrombosis formed after EVT may enlarge the aneurysm and compress the medulla oblongata even further, leading to postoperative deterioration and even death. ⁴

To date, no studies have been conducted to compare the efficacy of microsurgical clipping with the combination of aneurysmectomy and EVT for giant aneurysms of the intracranial VA. In this study, we performed a systematic review of the relevant literature to address this issue.

Materials and methods

Search strategy

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. Giant aneurysm of posterior circulation and giant aneurysm of vertebral artery were used as searching items. Eligible English language articles (case reports, case series, and studies of giant aneurysms of the VA) were identified by searching the PubMed database (the last searching date was 14 February 2021).

The reference lists of the identified articles were also manually searched for additional relevant studies. The inclusion criteria were as follows: (a) the full text was available; (b) complete clinical data were available; and (c) diameter greater than 2.5 cm or described as giant aneurysm. A flowchart of the selection process is shown in Figure 1.

Figure 1.

Flowchart of search strategy.

Statistical analysis

GraphPad software (LLC, San Diego, USA, 8.0) was used for statistical analysis. The continuous variables were expressed as mean ± standard deviation. If complying with Gaussian distribution, the t-test would be performed for continuous data. Otherwise, a non-parametric test would be performed. For count data, the chi-square test or Fisher’s exact test were used. P < 0.05 indicated a significant difference.

Results

A total of 45 articles containing 53 patients (53 aneurysms) were identified.^3–47 In addition to the 53 patients identified in the literature, we also included two typical cases for illustration which were not included in the final analysis (Figures 2, 3 and 4).

Figure 2.

Rapid neurological deterioration in a patient with ruptured intracranial giant VA aneurysm. (a) Head CT shows subarachnoid haemorrhage concentrated at the ambient cistern. (b)–(d) Axial (b), sagittal (c) and coronal (d) CT show the occupying lesion with medulla oblongata compression. (e) CTA reveals a giant aneurysm in the VA. (f) CT shows the size of the aneurysm and the residual cavity (filled with contrast agent). (g) and (h) Several hours after admission, the patient rapidly deteriorates. Head CT shows further effacement of the brainstem (g) and acute hydrocephalus (h). The patient died 16 hours after admission. CT: computed tomography; CTA: computed tomography angiography; L: left; VA: vertebral artery.

Figure 3.

Pre-procedural images of a patient with giant right VA aneurysm. (a) and (b) Sagittal MRI on T2 (a) and T1 (b) sequences show a thrombosed giant aneurysm in front of the medulla oblongata (asterisk) with severe brainstem compression. (c) Axial MRI on T2 sequence shows a thrombosed aneurysm in front of the medulla oblongata with severe brainstem compression. (d) MRI on T1 sequence shows slight dilation of the lateral ventricles. (e) CTA shows that the aneurysm is located at the right VA. Single and double arrowheads denote the VA proximal and distal to the aneurysm, respectively. (f) MIP image shows that the residual cavity of the aneurysm is filled with contrast agent. The patient is a 54-year-old man admitted for right limb weakness and dysphagia. AN: aneurysm; BA: basilar artery; CT: computed tomography; CTA: computed tomography angiography; L: left; MIP: maximal intensity projection; MRI: magnetic resonance imaging; R: right; VA: vertebral artery.

Figure 4.

Intraoperative and postoperative images of the afore-mentioned patient. (a) Angiogram of the left VA shows the left VA is displaced by the aneurysm. (b) Angiogram of the right VA shows the aneurysm. Asterisk denotes the residual cavity and T denotes the thrombosed part. (c) Angiogram of the right VA after further advancing the guiding catheter, the aneurysm is more clearly shown. A jet flow (arrowhead) is noted. Some small arteries (asterisk) originate from the VA proximal to the aneurysm. (d) The VA is occluded with coils proximal to the aneurysm. (e) Unsubtracted angiogram of the right VA shows the right VA is coiled (arrow). And there is contrast agent retention in the aneurysm cavity. (f) Angiogram of the left VA shows no evident bloodflow to the contralateral aneurysm. (g) and (h) The patient deteriorates 8 hours after EVT. Head CT shows that the aneurysm is filled with contrast agent and that the bilateral ventricles are dilated. The patient died 20 hours after EVT. AN: aneurysm; BA: basilar artery; EVT: endovascular treatment; VA: vertebral artery.

The patients were aged from 5 to 77 years (mean 48.8 ± 20.8 years). Thirty (58.8%, 30/51) patients were boys or men. On admission, five patients (9.4%, 5/53) lived independently, while the remaining 48 (90.6%, 48/53) patients were dependent on others. Two patients (3.8%, 2/53) were admitted for aneurysmal subarachnoid haemorrhage due to rupture of the VA aneurysms, and the remaining 51 (96.2%, 51/53) patients had unruptured aneurysms. The diameters of 25 aneurysms were not reported and only described as giant, and the diameters of the other 28 aneurysms ranged from 2.5 to 5 cm (mean 3.8 ± 0.7 cm).

Morphology and proportion of residual cavity

There were two cases without information on the morphology and proportion of residual cavity. Morphological details of the remaining 51 cases were as follows. Ten patients (19.6%, 10/51) had serpentine aneurysms, with the proportion of residual cavity being less than one-third in nine cases and more than two-thirds in one case. Ten patients (19.6%, 10/51) had irregular dissections, with the proportion of residual cavity being less than one-third in nine cases and more than two-thirds in one case. Twenty-four patients (47.1%, 24/51) had spherical dissections, with the proportion of residual cavity between one-third and two-thirds in four cases and more than two-thirds in 20 cases. Seven patients (13.7%, 7/51) had fusiform dissections, with the proportion of residual cavity being less than one-third in six cases and between one-third and two-thirds in one case.

Relationship between the aneurysm and medulla oblongata

Positional information was not available for one aneurysm. Of the remaining 52 aneurysms, 41 (78.8%, 41/52) were located at the midline of the medulla oblongata, and 11 (21.2%, 11/52) were located at one side of the medulla oblongata. In terms of the degree of aneurysmal compression to the medulla oblongata (Figure 5), 15 aneurysms (28.8%, 15/52) posed moderate compression to the medulla oblongata and 37 cases (71.1%, 37/52) posed severe compression.

Figure 5.

Illustration of the severity of medulla oblongata compression. (a) and (b) The diagrams in sagittal (a) and axial (b) views show that the medulla oblongata is moderately compressed (less than 50% of its anteroposterior diameter). (c) and (d) The diagrams in sagittal (a) and axial (b) views show that the medulla oblongata is severely compressed (more than 50% of its anteroposterior diameter). AN: aneurysm.

Treatment options

Four patients received conservative treatment (Table 1), and the remaining 49 patients received invasive treatment. The treated aneurysms were divided into two groups: the aneurysm removal group and the aneurysm reserve group. In the aneurysm removal group, partial or complete aneurysmectomy was performed after the aneurysm was trapped, leading to complete or partial decompression of the medulla oblongata. A bypass would be performed if necessary. Details of the aneurysm removal are illustrated in Figure 6.

Table 1.

Clinical data of the patients with conservative treatment.

No.	Author/year	Age/sex	Independence state at admission	Ruptured at admission	Size	Morphology and proportion of residual cavity	Positional relationship	Degree of brainstem compression	Cause of death
1	Nagahiro et al./1995 5	60/M	Dependent	No	5 cm	Serpentine, <1/3	Middle	Severe	Mass effect
2	Yasui et al./1998 6	76/M	Dependent	No	5 cm	Serpentine, <1/3	Lateral	Moderate	SAH
3	Inamasu et al./2000 7	54/M	Dependent	No	4.5 cm	Irregular, <1/3	Middle	Moderate	SAH
4	Ge et al./20168	65/F	Dependent	No	Giant	NM	NM	NM	SAH

F: female; M: male; NM: not mentioned; SAH: subarachnoid haemorrhage.

Figure 6.

Schematic diagram of treatments with aneurysmal removal. (a) The VA aneurysm is trapped with clips and partially removed. (b) The aneurysm is completely resected after trapping. (c) A VA or PICA bypass is performed after trapping and partially removing the aneurysm. (d) A VA or PICA bypass is performed after trapping and completely resecting the aneurysm. (e) and (f) For an eccentric aneurysm (e), the VA wall is sutured after clipping and removing the aneurysm (f). BA: basilar artery; PICA: posterior inferior cerebellar artery; VA: vertebral artery.

In the aneurysm reserve group, blood flow to the aneurysm was diminished or occluded by surgical or endovascular methods, without removing the aneurysm. Thus, the space-occupying effect was not relieved. The details of aneurysm reserve treatments are illustrated in Figure 7.

Figure 7.

Schematic diagram of treatments with aneurysm reserve. (a) The VA is clipped at the proximal end to reduce blood flow to the aneurysm. (b) The aneurysm is trapped with clips. (c) The VA is proximally occluded with coils or a balloon to reduce blood flow to the aneurysm. (d) The VA is proximally occluded with a balloon or coils, and the distal end of the aneurysm is coiled through the contralateral VA. (e) Both the VA and aneurysm are coiled. (f) The aneurysm is coiled with stent assistance. (g) The VA is reconstructed with a FDS alone. (h) The aneurysm is loosely coiled and the VA is reconstructed with a FDS. BA: basilar artery; FDS: flow-diverting stent; VA: vertebral artery.

Aneurysm removal group

Of the 17 patients receiving aneurysmal removal (Table 2), four (28.6%, 4/17) underwent complete aneurysmectomy, five (29.4%, 5/17) underwent partial aneurysmectomy, two (11.8%, 2/17) underwent partial aneurysmectomy in combination with bypass, three (17.6%, 3/17) underwent complete aneurysmectomy in combination with bypass, one (5.9%, 1/17) underwent complete aneurysmectomy in combination with suturing reconstruction and two (11.8%, 2/17) underwent aneurysmal clipping.

Table 2.

Clinical data of the patients with aneurysm removal.

No.	Author/year	Age/sex	Independence state at admission	Ruptured at admission	Size	Morphology and proportion of residual cavity	Positional relationship	Degree of brainstem compression	Treatment	Deterioration	Follow-up period	Outcome (GOS)
1	Sugita et al./19889	51/F	Dependent	No	4.5 cm	Serpentine; <1/3	Middle	Severe	Complete aneurysmectomy	Y	3 Months	4
2	Sugita et al./19889	61/M	Dependent	No	3.5 cm	Serpentine; <1/3	Middle	Severe	Complete aneurysmectomy	N	3 Months	3
3	Sugita et al./19889	65/M	Dependent	No	3.5 cm	Spherical; >2/3	Middle	Severe	Partial aneurysmectomy	N	6 Months	4
4	Sugita et al./19889	68/F	Dependent	No	2.5 cm	Spherical; >2/3	Middle	Severe	Aneurysmal clipping and complete aneurysmectomy	N	6 Months	5
5	Honda et al./199110	64/M	Dependent	No	Giant	Irregular dissection; <1/3	Lateral	Moderate	Complete aneurysmectomy + suturing reconstruction	N	3 Months	4
6	Wakui et al./199211	46/M	Dependent	No	5 cm	Serpentine; <1/3	Middle	Severe	Bypass + partial aneurysmectomy	Y	3 Months	4
7	Nagasawa et al./1994 12	42/M	Dependent	No	4 cm	Fusiform dissection; <1/3	Lateral	Moderate	Bypass + complete aneurysmectomy	Y	NA	1
8	Okudera et al./1994 13	57/M	Dependent	No	2.5 cm	NM	Lateral	Moderate	Partial aneurysmectomy	N	2 Years	4
9	Greene et al./1994 14	9/M	Dependent	No	Giant	Serpentine; <1/3	Middle	Severe	Partial aneurysmectomy	Y	2 Years	4
10	Nagahiro et al./1995 5	60/M	Dependent	No	4.5 cm	Serpentine; <1/3	Middle	Severe	Bypass + partial aneurysmectomy	Y	1 Year	4
11	Aoki et al./1997 15	65/M	Dependent	No	3.6 cm	Irregular dissection; <1/3	Middle	Severe	Complete aneurysmectomy	Y	2 Weeks	3
12	Iihara et al./2003 16	58/F	Dependent	No	Giant	Spherical dissection; >2/3	Middle	Moderate	Partial aneurysmectomy	Y	5 Months	4
13	Benes et al./2006 17	65/F	Dependent	No	Giant	Fusiform dissection; <1/3	Lateral	Moderate	Bypass + complete aneurysmectomy	N	7 Years	5
14	Grigoryan et al./2016 18	48/F	Dependent	No	4.3 cm	Spherical dissection; 1/3–2/3	Middle	Severe	Complete aneurysmectomy	Y	NM	3
15	Suzuki et al./2018 19	52/F	Dependent	No	Giant	Fusiform dissection; <1/3	Middle	Severe	Partial aneurysmectomy	N	1 Year	5
16	Jaikin et al./2018 20	11/M	Dependent	No	4 cm	Spherical dissection; >2/3	Middle	Moderate	Aneurysmal clipping and complete aneurysmectomy	N	13 Months	5
17	Tsunoda et al./2019 21	55/M	Dependent	No	Giant	Serpentine; <1/3	Middle	Severe	Bypass + complete aneurysmectomy	N	NM	5

F: female; GOS: Glasgow outcome scale; M: male; N: no; NA: not applicable; NM: not mentioned; Y: yes.

Aneurysm reserve group

Of the 32 cases (Table 3) receiving aneurysmal reserve, 10 (31.2%, 10/32) underwent proximal VA occlusion, 11 (34.4%, 11/32) underwent aneurysmal trapping, one (3.1%, 1/32) underwent coiling of the aneurysm, one (3.1%, 1/32) underwent coiling of the aneurysm and VA, one (3.1%, 1/32) underwent bypass and coiling of the aneurysm and VA, three (9.4%, 3/32) underwent stent-assisted coiling of the aneurysm, one (3.1%, 1/32) underwent VA reconstruction with flow-diverting stent (FDS), two (6.3%, 2/32) underwent partial coiling and VA reconstruction with FDS and two (6.3%, 2/32) underwent VA reconstruction with overlapping stents.

Table 3.

Clinical data of the patients with aneurysm reserve.

No.	Author/year	Age/sex	Independence state at admission	Ruptured at admission	Size	Morphology and proportion of residual cavity	Positional relationship	Degree of brainstem compression	Treatment	Deterioration	Treatment	Follow-up period	Aneurysm change after treatment	Outcome (GOS)
1	Guglielmi et al./198922	38/F	Dependent	No	Giant	Spherical dissection, >2/3	Lateral	Severe	Balloon occlusion of proximal VA	N	NA	12 Months	NM	4
2	Abe et al./199423	57/M	Dependent	No	Giant	Fusiform dissection, <1/3	Lateral	Moderate	Clipping of proximal VA	N	NA	1 Month	NM	5
3	Khayata et al./199424	5/M	Dependent	Yes	Giant	Serpentine, <1/3	Middle	Moderate	Bypass + trapping VA and aneurysm coiling	N	NA	3 Months	Shrink	5
4	Gurian et al./199525	37/F	Independent	No	Giant	Spherical dissection, >2/3	Middle	Severe	Balloon occlusion of proximal VA	Day 1; SAH	VA PAO and coiling	5 Months	NM	4
5	Chang et al./199926	72/F	Dependent	No	3 cm	Spherical dissection, >2/3	Middle	Severe	Balloon and coil occlusion of proximal VA	Day 9; mass effect	Conservative treatment	NA	NA	1
6	Piepgras et al./200127	27/F	Dependent	No	3 cm	Spherical dissection, >2/3	Middle	Severe	Balloon and coil occlusion of proximal VA	Day 7; mass effect	Aneurysmectomy	NA	NA	NA
7	Otsuka et al./200128	10/M	Dependent	No	3.3 cm	Serpentine, >2/3	Lateral	Moderate	Trapping VA with coils	N	NA	4 Months	Shrink	5
8	Leibowitz et al./200329	71/M	Dependent	No	Giant	Fusiform dissection, <1/3	Lateral	Moderate	Trapping VA with coils	N	NA	19 Months	Shrink	5
9	Morita et al./200330	65/F	Dependent	No	3 cm	Spherical dissection, >2/3	Middle	Severe	Occlusion of proximal VA with coils	Month 1; SAH	Aneurysm coiling	NA	NA	1
10	Lubicz et al./200431	52/M	Dependent	No	4 cm	Spherical dissection, 1/3-2/3	Middle	Severe	Trapping VA with coils	A few hours; mass effect	Conservative treatment	36 Months	Shrink	4
11	Iwabuchi et al./20054	72/F	Dependent	No	Giant	Spherical dissection, >2/3	Middle	Severe	Occlusion of proximal VA with coils	Day 9; SAH	Conservative treatment	NA	NA	1
12	Feddersen et al./200633	53/F	Dependent	No	Giant	Spherical dissection, >2/3	Middle	Severe	Coiling aneurysm	Day 4; bradycardia	Conservative treatment	NM	NM	5
13	Kasliwal et al./200734	20/F	Dependent	No	3.2 cm	Spherical dissection, >2/3	Middle	Severe	Trapping VA with coils	Day 3; mass effect	Conservative treatment	NA	NM	1
14	Terakawa et al./200835	52/F	Dependent	Yes	4.4 cm	Spherical dissection, 1/3–2/3	Middle	Severe	Clipping and coiling trapping VA and coiling aneurysm	N	NA	28 Months	Shrink	4
15	Limaye et al./201236	63/F	Independent	No	Giant	Spherical dissection, >2/3	Middle	Severe	Stent-assisted coiling	N	NA	6 Months	Unchanged	5
16	Saito et al./201337	70/F	Dependent	No	Giant	Fusiform dissection, <1/3	Middle	Severe	Clipping and coiling the proximal VA	Several weeks; mass effect	NA	Several months	Shrink	5
17	Chen et al./201338	21/M	Dependent	No	4.0 cm	Fusiform dissection, 1/3–2/3	Middle	Severe	Trapping VA with coils	N	Conservative treatment	3 Months	Shrink	5
18	Park et al./20143	7/F	Dependent	No	3.4 cm	Spherical dissection, >2/3	Middle	Severe	Occlusion of proximal VA with coils	Day 14; mass effect	Continuous coiling	2 Years	Shrink	5
19	Zarzecka et al./201432	15/F	Independent	No	Giant	Irregular dissection, >2/3	Lateral	Moderate	FDS	NO	Conservative treatment	2 Years	Disappear	5
20	Zhang et al./201439	44/F	Dependent	No	Giant	Spherical dissection, >2/3	Middle	Severe	Stent-assisted coiling	Immediately; SAH	Conservative treatment	NA	NA	1
21	Lee et al./201640	60/M	Dependent	No	4 cm	Spherical dissection, >2/3	Middle	Severe	Coiling trapping VA	Day 7; mass effect	NA	NA	NA	NA
22	Zhang et al./201641	55/M	Dependent	No	3.1 cm	Irregular dissection, <1/3	Middle	Severe	Trapping VA with coils	Immediately; mass effect	Conservative treatment	26 Months	Enlarge	3
23	Zhang et al./201641	53/M	Dependent	No	Giant	Irregular dissection, <1/3	Middle	Severe	Trapping VA with coils	N	NA	4 Months	Unchanged	3
24	Zhang et al./201641	57/M	Dependent	No	Giant	Irregular dissection, <1/3	Middle	Severe	Trapping VA with coils	Progressive deterioration after surgery; mass effect	Conservative treatment	3 Months	Enlarge	3
25	Pahl et al./201642	54/M	Dependent	No	Giant	Irregular dissection, <1/3	Middle	Severe	Trapping VA and coiling	Progressive deterioration after surgery; mass effect	Aneurysmectomy	NA	NA	NA
26	Ge et al./20168	77/M	Dependent	No	Giant	Spherical dissection, >2/3	Middle	Severe	Stent-assisted coiling	Day 5; SAH	Conservative treatment	NA	NA	1
27	Murai et al./201743	71/M	Dependent	No	4.2 cm	Irregular dissection, <1/3	Middle	Severe	Trapping aneurysm with clips	Day 5; infarction	Conservative treatment	12 Months	NM	3
28	Morishita et al./201744	56/M	Dependent	No	Giant	Irregular dissection, <1/3	Middle	Moderate	PAO of proximal VA	N	NA	NM	NM	5
29	Wang et al./201945	12/M	Independent	No	Giant	Spherical dissection, >2/3	Middle	Severe	FDS + partial coiling	N	NA	6 Months	Shrink	5
30	Shirani et al./202046	12/M	Independent	No	Giant	Spherical dissection, >2/3	Middle	Severe	FDS + coiling	N	NA	6 Months	NM	5
31	Suzuki et al./202047	NM/NM	Dependent	No	3.8cm	Spherical dissection, >2/3	Lateral	Moderate	Overlapping stents	N	NA	6 Months	Shrink	5
32	Suzuki et al./202047	NM/NM	Dependent	No	3.5cm	Spherical dissection, 1/3–2/3	Middle	Severe	Overlapping stents	N	NA	12 Months	Enlarge	NA

F: female; FDS: flow-diverting stent; GOS: Glasgow outcome scale; M: male; N: no; NM: not mentioned; NA: not applicable; PAO: parent artery occlusion; SAH: subarachnoid haemorrhage; VA: vertebral artery; Y: yes.

Outcome

Conservative treatment group

All the four patients died during conservative treatment.

Aneurysm removal group

Eight (47.1%, 8/17) of the 17 patients experienced neurological exacerbation after surgery. The follow-up period ranged from 3 to 84 months. The Glasgow outcome scale (GOS) scores of the patients were 1, 3, 4 and 5 in one (5.9%, 1/17), three (17.6%, 3/17), eight (47.1%, 8/17) and five (29.4%, 5/17) patients, respectively.

Aneurysm reserve group

Of the 32 patients, 17 (53.1%, 17/32) experienced neurological exacerbation postoperatively, of whom five exacerbated immediately after surgery, seven exacerbated in the first week, three between 1 and 2 weeks, and two beyond 2 weeks. The follow-up period ranged from one to 48 months. Sixteen patients underwent postoperative imaging follow-up, three aneurysms grew, 10 shrank, one disappeared and two remained unchanged. The GOS scores were available in 28 patients, that were 1, 3, 4 and 5 in six (21.4%, 6/28), four (14.3%, 4/28), four (14.3%, 4/28) and 14 (50%, 14/28) patients, respectively.

Statistical analysis

Baseline data

Age, sex, whether the patient was independent, mode of onset (ruptured or unruptured), aneurysm size, proportion of residual cavity greater than two-thirds, aneurysm position and severity of medulla oblongata compression did not differ significantly between the two groups, indicating that the baseline data were comparable (Table 4).

Table 4.

Comparison of the baseline data and treatment results between the aneurysm removal group and the aneurysm reserve group.

	Aneurysm removal group (n = 17)	Aneurysm reserve group (n = 32)	P value
Age	9–68 years (51.6 ± 17.3) (n = 17)	5–77 years (45.3 ± 22.9) (n = 30)	0.3287
Sex	11 M, 6 F (n = 17)	16 M, 14 F (n = 30)	0.5460
Independent	0 (n = 17)	5 (n = 32)	0.1488
SAH	0 (n = 17)	2 (n = 32)	0.5374
Size	2.5–5 (3.8±0.8) (n = 11)	3–4.4 (3.6 ± 0.5) (n = 14)	0.3538
Proportion of residual cavity >2/3 on angiogram	4 (n = 16)	18 (n = 32)	0.0650
Middle position	13 (n = 17)	26 (n = 32)	0.7215
Severe brainstem compression	11 (n = 17)	25 (n = 32)	0.3309
Death	1 (n = 17)	6 (n = 28)	0.2196
GOS 4–5	13 (n = 17)	18 (n = 28)	0.5134

The t-test was used to compare the age and aneurysm size between two groups, and the remaining indexes were compared by the chi-square test.

F: female; GOS: Glasgow outcome scale; M: male; SAH: subarachnoid haemorrhage.

Treatment results

The occurrence of postoperative deterioration, the occurrence of death and the prognosis did not differ significantly between the two groups. The details are summarised in Table 4.

Discussion

Giant aneurysms of the intracranial VA are rare intracranial lesions, and only 53 reported cases were identified in this review.^3–47 The intracranial segment of the VA runs along the anterolateral aspect of the medulla oblongata. Aneurysms originating from the intracranial segment of VA are rare and often dissecting aneurysms, ⁴⁸ and most of them are stable and do not rupture. Some VA aneurysms may progressively grow into giant aneurysms. The growth of giant aneurysms is related to intra-aneurysm thrombosis, repeated bleeding and reconstruction of the aneurysm wall. ⁴⁹

During the growth of intracranial VA aneurysms, the medulla oblongata would endure progressive compression, leading to the thinning and elongation of the medulla oblongata. In extreme circumstances, the normal medulla oblongata tissue could even not be observed on axial magnetic resonance scans (Figure 3(c)). As this process is slow, some patients may only have slight or even no symptoms due to the compensatory ability of the medulla oblongata. ⁴¹ In fact, detailed physical examination may reveal the subtle symptoms of medulla oblongata, cerebellum and cranial nerve compression. The clinical symptoms are not only related to the degree of compression on the medulla oblongata but are also related to their positional relationship. When the aneurysm is located at one side, part of the medulla oblongata may function normally, leading to mild clinical symptoms.

Medulla oblongata compression caused by a giant aneurysm of the intracranial VA may lead to a poor outcome. For example, all the patients treated with conservative management died (Table 1), indicating that the natural history of giant aneurysm in this region is aggressive. ⁵⁰ Therefore, this finding is consistent with that of previous studies, suggesting that giant dissecting aneurysms of the intracranial VA should be aggressively treated either by open surgery or EVT. However, simple stratification of the results according to the treatments failed to reveal the treatment nature. The main factor that determines the treatment selection is whether it can relieve the mass effect on the medulla oblongata.

Therefore, in this study, the patients with aggressive treatment were divided into two groups: the aneurysm removal group and the aneurysm reserve group. The baseline data did not differ significantly between the two groups, and thus, comparison of the prognosis between the two groups may reflect the differences in treatment efficacy.

Theoretically, it is important to remove the aneurysm, thereby directly relieving the mass effect of the aneurysm on the medulla oblongata. However, it is very difficult to remove giant aneurysms in this region. They often adhere to the lower cranial nerves and medulla oblongata or obscure the surrounding important neurovascular structures. Consequently, exposing aneurysms can cause inadvertent injuries and even severe complications. In addition, the posterior inferior cerebellar artery is often involved, and a bypass is often needed. Hence, surgical procedures aimed at removing the giant aneurysm have a high risk.^12,21

Previously, for treating giant VA aneurysms with aneurysm reserving, balloons or clips were usually used to occlude or reduce blood flow to the aneurysm.^22,23 In recent years, many EVT materials have been developed, making it possible to trap aneurysms both at the proximal and distal ends. Of note, coils are not routinely used, because they might increase the aneurysm size. In addition to aneurysm trapping, conventional stent-assisted coiling and FDSs have also been used. ⁴⁶ However, treatments with aneurysm reserving may lead to postprocedural enlargement of the aneurysm due to thrombus formation in the aneurysm cavity, and thus resulting in catastrophic consequences. Postprocedural deterioration after EVT may occur within the first month.

Conclusion

Despite decades of exploration, it is still difficult to manage giant intracranial VA aneurysms, regardless of the treatment selected. In this review, a satisfactory outcome was achieved in 68.9% of the cases. Because of the malignant natural history, aggressive treatment is still advocated.