**2. Short history and evolution of aneurysm surgery**

Although the pathology of intracranial aneurysms had been scrupulously studied by the beginning of the twentieth century, treatment options were scarce and most often fruitless [1]. Harvey Cushing (1869–1939) himself doubted whether these lesions could be approached surgically due to the technical limitations, reduced accessibility and visibility of the lesions, as well as a general lack of experience in the surgical community [1–3]. Up until that point, the treatment of intracranial aneurysms relied on the proximal ligation technique, as described by John Hunter (1728–1793). This resulted in thrombosis and occlusion inside the aneurysm. In 1885, Sir Victor Horsley (1857–1916) was reportedly the first to successfully perform such an intervention for an intracranial aneurysm by ligating the right common carotid artery [1, 2, 4]. Cushing is credited with developing the wrapping technique for the treatment of intracranial aneurysms; however, in 1931 his pupil, Dott Norman McComish (1897–1973), performed the first elective frontal craniotomy in order to wrap and reinforce a ruptured aneurysm with autologous muscle from the patient's thigh [3–5]. Axel Herbert Olivecrona (1891–1980) was the first to perform a successful surgical trapping and removal of an intracranial aneurysm in 1932, a technique then further elaborated by Walter Dandy (1886–1946) [5]. In 1937, Dandy used a modified version of the Cushing clip to occlude a posterior communicating artery (PCoA) aneurysm via a "hypophyseal approach," being the first ever documented intervention of its kind [1, 2–5].

**149**

time [4, 5, 15, 16].

*Preventing Rupture: Clipping of Unruptured Intracranial Aneurysms*

Since then, aneurysm clipping has undergone extensive improvements in both technique and instrumentation. The Cushing clip was malleable; however, according to Kenneth George McKenzie (1892–1964), the two sides of the clips were frequently of unequal length, had rough ends, and had a habit of turning in the holder [6]. Furthermore, it could not be reopened or repositioned; thus, an improper placement could compromise the entire intervention [5]. In 1927, McKenzie conceived a more versatile alternative to the instruments used [6–9]. In 1949, Duane William Jr. changed the McKenzie-modified clip holder to punch out more effective U-shaped clips [5]. Olivecrona made a considerable redesign of the clips in 1953 that allowed reopening and repositioning of the clips [4, 5, 9]. However, the drawback to these clips were crushing the aneurysmal neck and producing shearing and tearing of the fragilized vascular walls. Thus, Henry Schwartz introduced the cross-action alpha clip, basically a miniaturized spring forceps that could close by itself [3, 5, 9]. Despite this concept being brilliant, its utilization in aneurysm surgery was problematic due to its large size and the bulkiness of its applicator. In 1952, Frank Mayfield and George Kees Jr. made delicate yet crucial enhancements to clip technology, significantly reducing the size of the shank, while also constructing clips of diverse lengths and angles, as well as having wider blade openings [3–5, 9–11]. They were also responsible for the bayoneted design of the clip that would permit better visualization during manipulation. Joseph McFadden suggested a modification of Kees' design, with rounded blades

Charles Drake (1920–1998) was credited with developing the fenestrated clip in 1969, which could allow placement of the clips on more inaccessible aneurysms without compromising the parent vessel [1, 3, 4]. This was especially useful for treating posterior fossa aneurysms, for which Drake also pioneered innovative techniques and surgical approaches (such as the subtemporal approach for aneurysms of the basilar apex) [4]. George Smith (1916–1964) also made an essential innovation with a vessel-encompassing clip that could occlude aneurysms on the opposite side of the affected artery [3, 12]. Elaborating on this concept, Thoralf Sundt (1930–1992) devised a Teflon-lined clip-graft that could also mend small tears or irregularities in the artery [1, 3–5, 12, 13]. At present, adjustments are still

made regarding configuration, instrumentation, and clip composition.

The next most important bound in aneurysm surgery came in the form of the operating microscope, allowing better visualization and illumination of the aneurysm neck and surrounding vessels [1, 4, 5, 14]. Gazi Yasargil, the father of microneurosurgery, had probably the greatest contribution in this field by not only standardizing the use of the operating microscope in aneurysm surgery but also by developing and refining procedures and instruments now commonly used in vascular neurosurgery [1, 3, 4]. The clips he created were specifically designed for use alongside microscopic magnification. Moreover, he also underscored the necessity of understanding cisternal and microvascular anatomy in neurosurgery. Drake's seemingly most remarkable addition to vascular neurosurgery was comprehending the intricate anatomy of posterior circulation aneurysms, as well as improving outcomes following their surgical treatment [4, 5]. Magnetic resonance imaging (MRI) became crucial in the diagnosis of cerebrovascular pathologies. Although, since the first clips introduced in neurosurgery were made of stainless steel, they were not compatible with MRI. After rigorous compatibility testing, Robert Spetzler introduced the pure titanium clips as a nonferromagnetic alternative with the same mechanical properties as other clips available at that

Yasargil also described the end-to-side anastomosis between the superficial temporal artery and middle cerebral artery (MCA), which bypassed the blood

*DOI: http://dx.doi.org/10.5772/intechopen.88038*

and blunted tips [3, 11].

#### *Preventing Rupture: Clipping of Unruptured Intracranial Aneurysms DOI: http://dx.doi.org/10.5772/intechopen.88038*

*New Insight into Cerebrovascular Diseases - An Updated Comprehensive Review*

the surgical management of unruptured and multiple aneurysms.

life-saving option.

neurological outcome.

opening surgical treatment of multiple UIAs.

ever documented intervention of its kind [1, 2–5].

**2. Short history and evolution of aneurysm surgery**

procedure. In this chapter, we present our considerable experience and attitude in

Preventing rupture from IAs represents a major concern for neurosurgeons, neuroradiologists, and neurointerventionists, as this represents a catastrophic and potentially life-threatening occurrence in the natural history of this pathology. UIAs are defined as not possessing a known history or signs of rupture or that have been diagnosed incidentally for symptoms unrelated to intracranial hemorrhage. They are a veritable "ticking time bomb" that, under certain conditions, can "detonate" and cause a devastating hemorrhagic stroke with severe and often irreversible consequences. Therefore, preventive surgical treatment of UIAs, especially clipping of the aneurysmal sack, is a valuable and possibly

A successful clipping means that the vascular clip completely isolates the aneurysmal lumen from blood flow at its origin on the parent artery. This point of origin is generally located at either a bifurcation or a sharp turn of an artery. Surgical clipping may prevent rupture of that particular aneurysm, although an incomplete occlusion can result in recurrence. Since the development of less invasive endovascular techniques, clipping has lost most of its standing in the treatment of UIAs, being reserved for hemorrhagic lesions or those otherwise unsuitable for endovascular procedures. Certain highly experienced centers still favor the intracranial approach for UIAs due to the longevity of procedure and excellent postoperative

Additionally, some patients may harbor more than one aneurysm, occurring either concomitantly or sequentially. These may be diagnosed incidentally, during the rupture of at least one of the aneurysms or at a variable point in time during postprocedural control. The treatment of multiple intracranial aneurysms (MIAs) to this day remains a highly debated topic, lacking a general consensus regarding indications, timing, and modality. Our experience supports the single-stage single-

Although the pathology of intracranial aneurysms had been scrupulously studied by the beginning of the twentieth century, treatment options were scarce and most often fruitless [1]. Harvey Cushing (1869–1939) himself doubted whether these lesions could be approached surgically due to the technical limitations, reduced accessibility and visibility of the lesions, as well as a general lack of experience in the surgical community [1–3]. Up until that point, the treatment of intracranial aneurysms relied on the proximal ligation technique, as described by John Hunter (1728–1793). This resulted in thrombosis and occlusion inside the aneurysm. In 1885, Sir Victor Horsley (1857–1916) was reportedly the first to successfully perform such an intervention for an intracranial aneurysm by ligating the right common carotid artery [1, 2, 4]. Cushing is credited with developing the wrapping technique for the treatment of intracranial aneurysms; however, in 1931 his pupil, Dott Norman McComish (1897–1973), performed the first elective frontal craniotomy in order to wrap and reinforce a ruptured aneurysm with autologous muscle from the patient's thigh [3–5]. Axel Herbert Olivecrona (1891–1980) was the first to perform a successful surgical trapping and removal of an intracranial aneurysm in 1932, a technique then further elaborated by Walter Dandy (1886–1946) [5]. In 1937, Dandy used a modified version of the Cushing clip to occlude a posterior communicating artery (PCoA) aneurysm via a "hypophyseal approach," being the first

**148**

Since then, aneurysm clipping has undergone extensive improvements in both technique and instrumentation. The Cushing clip was malleable; however, according to Kenneth George McKenzie (1892–1964), the two sides of the clips were frequently of unequal length, had rough ends, and had a habit of turning in the holder [6]. Furthermore, it could not be reopened or repositioned; thus, an improper placement could compromise the entire intervention [5]. In 1927, McKenzie conceived a more versatile alternative to the instruments used [6–9]. In 1949, Duane William Jr. changed the McKenzie-modified clip holder to punch out more effective U-shaped clips [5]. Olivecrona made a considerable redesign of the clips in 1953 that allowed reopening and repositioning of the clips [4, 5, 9]. However, the drawback to these clips were crushing the aneurysmal neck and producing shearing and tearing of the fragilized vascular walls. Thus, Henry Schwartz introduced the cross-action alpha clip, basically a miniaturized spring forceps that could close by itself [3, 5, 9]. Despite this concept being brilliant, its utilization in aneurysm surgery was problematic due to its large size and the bulkiness of its applicator. In 1952, Frank Mayfield and George Kees Jr. made delicate yet crucial enhancements to clip technology, significantly reducing the size of the shank, while also constructing clips of diverse lengths and angles, as well as having wider blade openings [3–5, 9–11]. They were also responsible for the bayoneted design of the clip that would permit better visualization during manipulation. Joseph McFadden suggested a modification of Kees' design, with rounded blades and blunted tips [3, 11].

Charles Drake (1920–1998) was credited with developing the fenestrated clip in 1969, which could allow placement of the clips on more inaccessible aneurysms without compromising the parent vessel [1, 3, 4]. This was especially useful for treating posterior fossa aneurysms, for which Drake also pioneered innovative techniques and surgical approaches (such as the subtemporal approach for aneurysms of the basilar apex) [4]. George Smith (1916–1964) also made an essential innovation with a vessel-encompassing clip that could occlude aneurysms on the opposite side of the affected artery [3, 12]. Elaborating on this concept, Thoralf Sundt (1930–1992) devised a Teflon-lined clip-graft that could also mend small tears or irregularities in the artery [1, 3–5, 12, 13]. At present, adjustments are still made regarding configuration, instrumentation, and clip composition.

The next most important bound in aneurysm surgery came in the form of the operating microscope, allowing better visualization and illumination of the aneurysm neck and surrounding vessels [1, 4, 5, 14]. Gazi Yasargil, the father of microneurosurgery, had probably the greatest contribution in this field by not only standardizing the use of the operating microscope in aneurysm surgery but also by developing and refining procedures and instruments now commonly used in vascular neurosurgery [1, 3, 4]. The clips he created were specifically designed for use alongside microscopic magnification. Moreover, he also underscored the necessity of understanding cisternal and microvascular anatomy in neurosurgery. Drake's seemingly most remarkable addition to vascular neurosurgery was comprehending the intricate anatomy of posterior circulation aneurysms, as well as improving outcomes following their surgical treatment [4, 5]. Magnetic resonance imaging (MRI) became crucial in the diagnosis of cerebrovascular pathologies. Although, since the first clips introduced in neurosurgery were made of stainless steel, they were not compatible with MRI. After rigorous compatibility testing, Robert Spetzler introduced the pure titanium clips as a nonferromagnetic alternative with the same mechanical properties as other clips available at that time [4, 5, 15, 16].

Yasargil also described the end-to-side anastomosis between the superficial temporal artery and middle cerebral artery (MCA), which bypassed the blood

flow from the extracranial circulation to the intracranial compartment [5]. The bypass techniques are currently used in the management of more complex giant aneurysms, however with less satisfactory outcomes than the standard surgical approaches for smaller aneurysms [5, 17]. A more recent advancement has been the introduction of intraoperative videoangiography by means of fluorescent dyes such as fluorescein sodium or indocyanine green [18]. Charles Wrobel first described this method in 1994 for real-time testing of aneurysmal obliteration and the patency of adjacent arteries [5, 19]. This tool renders intraoperative catheter-based angiography or Doppler ultrasonography obsolete in certain cases and allows repositioning of inconveniently placed clips before the onset of permanent damage [5, 18–20]. Other contemporary innovations include the endoscopic endonasal approaches in order to clip skull base aneurysms; however, this technique awaits further validation [5, 21–23].

Evidently, not all aneurysms were amenable to clipping. Before the dawn of endovascular procedures, surgeons attempted various methods of introducing foreign materials into the aneurysm sack to achieve thrombosis, with variable results. The materials ranged from heated silver enameled wire [24], copper wire [25], and silk sutures [26], to magnetically guided iron suspensions [27] to even animal hair from horse or dog [28]. Despite these techniques being mostly obsolescent, they indisputably paved the way to endovascular treatment of intracranial vasculopathies. The most important step in this direction belonged to the invention of the angiography as a superior instrument for diagnosing intracranial pathologies. The first cerebral angiography was performed by Egas Moniz (1874–1955) in 1927, a technique which remained the only dependable diagnostic method for identifying intracranial lesions until the introduction of computed tomography (CT) nearly 50 years later [1, 4, 29–31]. Fascinatingly enough, an editorial published in The Lancet in 1931 predicted the probability of not only diagnosing intracranial aneurysms through this tool but also as an opportunity for therapy in later years [1, 29]. The endovascular coils presently used were preceded by detachable balloons that could be deployed inside vascular lesions and would harden to result in a controlled localized thrombosis [1, 4, 32]. However, this technique resulted in significant complications and was soon replaced. The first successful treatment of an intracranial aneurysm via coiling belonged to Ira Braun in 1985 [1, 4]. Guido Guglielmi undoubtedly had the most significant role in developing modern coils that were electrolytically detachable [33–35].

Ever since, the role of microneurosurgery in the treatment of aneurysms has diminished in the face of a safer, easier, less invasive, and satisfyingly durable procedure with a shorter hospital stay and faster recovery time [36–38]. Many other endovascular techniques and tools have been elaborated in the wake of this innovation the technology experiencing an exponential growth. A thorough description of such instruments is beyond the scope of this chapter. In what follows, we detail the microsurgical treatment options for unruptured solitary and multiple aneurysms, with a special emphasis on clipping, its effects, outcome, and consequences while also sharing our operative experience.

#### **3. Natural history of unruptured aneurysms**

To quote physicist Niels Bohr (1885–1962), "Prediction is very difficult, especially about the future." This also applies to UIAs regarding what can cause them to bleed and when. There is a high variability between populations in the prevalence of UIAs, being cited between 1% and as much as 7% of the general population [39–42]. They are more commonly found in the anterior circulation,

**151**

intracranial aneurysm [54].

statement, as illustrated in **Figure 1**.

*Preventing Rupture: Clipping of Unruptured Intracranial Aneurysms*

at more advanced ages, and more often in women. The natural history seems to differ according to the shape, location, and size of the lesion, with a significant incongruity between the number of incidentally discovered aneurysms each year (2000–4000 per 100,000 persons/year) and the annual incidence of aneurysmal subarachnoid hemorrhage (aSAH) (approximately 10 per 100,000 persons/year) [43]. In other words, out of 200 to 400 patients diagnosed yearly with an intracranial aneurysm, chances are that only one of these may rupture. The annual and cumulative risk of rupture has been appraised at approximately 1%/year and at 9% at 9 years for the Japanese and Korean populations [44], similar to that of Western countries (0.2–1.6%/year and 10% at 10 years) [45–48]. Factors attributed to impact the natural history of UIAs may be related to the aneurysm itself, the

Concerning patient-related factors, it seems that women have a higher prevalence of UIAs than men, and the peak incidence was found between the fifth and sixth decades of age. Patients with polycystic kidney disease, type IV Ehlers-Danlos syndrome, and Marfan syndrome are more likely to develop UIAs during their lifetime. Hypertension is the comorbidity most likely associated with this finding, while a positive family history is also an important risk factor among siblings. Up to 15–30% of these patients harbor at least two UIAs, either concomitantly or sequentially. The most common modifiable risk factors attributed to UIAs are smoking,

alcohol and drug abuse, as well as using oral contraceptives [49].

According to the results of the PHASE 2 of the International Study of Unruptured Intracranial Aneurysms (ISUIA) trial, patients that had no previous aSAH and harbored aneurysms under 7 mm in diameter possessed no risk of rupture for UIAs in the anterior circulation [50]. However, the risk of bleeding was 2.5%/year for aneurysms located at the PCoA and the posterior cerebral circulation. Concerning patients with a history of aSAH, the risk of rupture for aneurysms smaller than 7 mm in the anterior cerebral circulation reached 1.5%/ year, whereas for the posterior circulation, it rose to 3.4%/year. Similarly, the Unruptured Cerebral Aneurysm Study (UCAS) performed in Japan proved that size influenced the risk of rupture, starting from 0.36% for microaneurysms (between 3 and 4 mm), climbing at 4.37% for lesions between 10 to 24 mm to reaching as much as 33.4% for giant aneurysms (≥25 mm) [42]. Analogous results were also reported for the South Korean population [44]. Apparently, as an aneurysm swells, the risk of subsequent rupture rises [51]. However, according to Serrone et al., the single predictor of aneurysm enlargement was the initial size of the lesion, with the annual risk of growth being evaluated at a mean of 3.5%, though higher for larger aneurysms [52]. The morphology of the aneurysm was also incriminated in influencing the risk of rupture, especially the formation of a daughter sac, the shape of the sac, and regions possessing a thinned arterial wall [53]. Pertaining to UIAs selected for conservative treatment, Ramachandran stated that "None of the metrics—including aneurysm size, nonsphericity index, peak wall tension, and low shear stress area—differentiated the stable from unstable groups with statistical significance," suggesting that there might not actually be such a thing as a "stable"

Aneurysmal rupture can also occur during stressful or strenuous activities such as sexual intercourse, labor, defecation, physical exertion, or sports [55]. However, these external factors may in fact conceal the climate impact, as numerous studies indicate a higher incidence of aneurysm rupture during the winter season, as well as during daytime [56–59]. Our experience of operated aneurysms also supports this

In summary, the natural history of aneurysms is complicated and shrouded in

uncertainty, except for one surety: UIAs do not spontaneously heal.

*DOI: http://dx.doi.org/10.5772/intechopen.88038*

patient, or even external influences.

#### *Preventing Rupture: Clipping of Unruptured Intracranial Aneurysms DOI: http://dx.doi.org/10.5772/intechopen.88038*

*New Insight into Cerebrovascular Diseases - An Updated Comprehensive Review*

flow from the extracranial circulation to the intracranial compartment [5]. The bypass techniques are currently used in the management of more complex giant aneurysms, however with less satisfactory outcomes than the standard surgical approaches for smaller aneurysms [5, 17]. A more recent advancement has been the introduction of intraoperative videoangiography by means of fluorescent dyes such as fluorescein sodium or indocyanine green [18]. Charles Wrobel first described this method in 1994 for real-time testing of aneurysmal obliteration and the patency of adjacent arteries [5, 19]. This tool renders intraoperative catheter-based angiography or Doppler ultrasonography obsolete in certain cases and allows repositioning of inconveniently placed clips before the onset of permanent damage [5, 18–20]. Other contemporary innovations include the endoscopic endonasal approaches in order to clip skull base aneurysms; however, this technique awaits further valida-

Evidently, not all aneurysms were amenable to clipping. Before the dawn of endovascular procedures, surgeons attempted various methods of introducing foreign materials into the aneurysm sack to achieve thrombosis, with variable results. The materials ranged from heated silver enameled wire [24], copper wire [25], and silk sutures [26], to magnetically guided iron suspensions [27] to even animal hair from horse or dog [28]. Despite these techniques being mostly obsolescent, they indisputably paved the way to endovascular treatment of intracranial vasculopathies. The most important step in this direction belonged to the invention of the angiography as a superior instrument for diagnosing intracranial pathologies. The first cerebral angiography was performed by Egas Moniz (1874–1955) in 1927, a technique which remained the only dependable diagnostic method for identifying intracranial lesions until the introduction of computed tomography (CT) nearly 50 years later [1, 4, 29–31]. Fascinatingly enough, an editorial published in The Lancet in 1931 predicted the probability of not only diagnosing intracranial aneurysms through this tool but also as an opportunity for therapy in later years [1, 29]. The endovascular coils presently used were preceded by detachable balloons that could be deployed inside vascular lesions and would harden to result in a controlled localized thrombosis [1, 4, 32]. However, this technique resulted in significant complications and was soon replaced. The first successful treatment of an intracranial aneurysm via coiling belonged to Ira Braun in 1985 [1, 4]. Guido Guglielmi undoubtedly had the most significant role in developing modern coils that were

Ever since, the role of microneurosurgery in the treatment of aneurysms has diminished in the face of a safer, easier, less invasive, and satisfyingly durable procedure with a shorter hospital stay and faster recovery time [36–38]. Many other endovascular techniques and tools have been elaborated in the wake of this innovation the technology experiencing an exponential growth. A thorough description of such instruments is beyond the scope of this chapter. In what follows, we detail the microsurgical treatment options for unruptured solitary and multiple aneurysms, with a special emphasis on clipping, its effects, outcome, and consequences while

To quote physicist Niels Bohr (1885–1962), "Prediction is very difficult, especially about the future." This also applies to UIAs regarding what can cause them to bleed and when. There is a high variability between populations in the prevalence of UIAs, being cited between 1% and as much as 7% of the general population [39–42]. They are more commonly found in the anterior circulation,

**150**

tion [5, 21–23].

electrolytically detachable [33–35].

also sharing our operative experience.

**3. Natural history of unruptured aneurysms**

at more advanced ages, and more often in women. The natural history seems to differ according to the shape, location, and size of the lesion, with a significant incongruity between the number of incidentally discovered aneurysms each year (2000–4000 per 100,000 persons/year) and the annual incidence of aneurysmal subarachnoid hemorrhage (aSAH) (approximately 10 per 100,000 persons/year) [43]. In other words, out of 200 to 400 patients diagnosed yearly with an intracranial aneurysm, chances are that only one of these may rupture. The annual and cumulative risk of rupture has been appraised at approximately 1%/year and at 9% at 9 years for the Japanese and Korean populations [44], similar to that of Western countries (0.2–1.6%/year and 10% at 10 years) [45–48]. Factors attributed to impact the natural history of UIAs may be related to the aneurysm itself, the patient, or even external influences.

Concerning patient-related factors, it seems that women have a higher prevalence of UIAs than men, and the peak incidence was found between the fifth and sixth decades of age. Patients with polycystic kidney disease, type IV Ehlers-Danlos syndrome, and Marfan syndrome are more likely to develop UIAs during their lifetime. Hypertension is the comorbidity most likely associated with this finding, while a positive family history is also an important risk factor among siblings. Up to 15–30% of these patients harbor at least two UIAs, either concomitantly or sequentially. The most common modifiable risk factors attributed to UIAs are smoking, alcohol and drug abuse, as well as using oral contraceptives [49].

According to the results of the PHASE 2 of the International Study of Unruptured Intracranial Aneurysms (ISUIA) trial, patients that had no previous aSAH and harbored aneurysms under 7 mm in diameter possessed no risk of rupture for UIAs in the anterior circulation [50]. However, the risk of bleeding was 2.5%/year for aneurysms located at the PCoA and the posterior cerebral circulation. Concerning patients with a history of aSAH, the risk of rupture for aneurysms smaller than 7 mm in the anterior cerebral circulation reached 1.5%/ year, whereas for the posterior circulation, it rose to 3.4%/year. Similarly, the Unruptured Cerebral Aneurysm Study (UCAS) performed in Japan proved that size influenced the risk of rupture, starting from 0.36% for microaneurysms (between 3 and 4 mm), climbing at 4.37% for lesions between 10 to 24 mm to reaching as much as 33.4% for giant aneurysms (≥25 mm) [42]. Analogous results were also reported for the South Korean population [44]. Apparently, as an aneurysm swells, the risk of subsequent rupture rises [51]. However, according to Serrone et al., the single predictor of aneurysm enlargement was the initial size of the lesion, with the annual risk of growth being evaluated at a mean of 3.5%, though higher for larger aneurysms [52]. The morphology of the aneurysm was also incriminated in influencing the risk of rupture, especially the formation of a daughter sac, the shape of the sac, and regions possessing a thinned arterial wall [53]. Pertaining to UIAs selected for conservative treatment, Ramachandran stated that "None of the metrics—including aneurysm size, nonsphericity index, peak wall tension, and low shear stress area—differentiated the stable from unstable groups with statistical significance," suggesting that there might not actually be such a thing as a "stable" intracranial aneurysm [54].

Aneurysmal rupture can also occur during stressful or strenuous activities such as sexual intercourse, labor, defecation, physical exertion, or sports [55]. However, these external factors may in fact conceal the climate impact, as numerous studies indicate a higher incidence of aneurysm rupture during the winter season, as well as during daytime [56–59]. Our experience of operated aneurysms also supports this statement, as illustrated in **Figure 1**.

In summary, the natural history of aneurysms is complicated and shrouded in uncertainty, except for one surety: UIAs do not spontaneously heal.

#### **Figure 1.**

*Multiannual incidence of aneurysmal rupture, as hospitalized and surgically treated in our institution between January and December 2017.*
