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Posterior communicating artery (PCoA) aneurysm is the aneurysm that arises at junction of internal carotid (IC) and PCoA. This aneurysm accounts for 15–25% of all intracranial aneurysm [1, 2]. If the aneurysm neck arises along the PCoA itself, it’s called “true” PCoA aneurysm, and this accounts more or less 1.3% of all intracranial aneurysm and 6.8% of all PCoA aneurysm [3].

Anterior choroidal artery aneurysms (AChAA) are comparatively rare and appear with a frequency from around 2–4% to 10% in larger series, e.g., M Lawton personal series of 2500 clipped aneurysms:  = 98 AChA = 4% [1]. Number of AChAA in treated aneurysms of BRAT study 2.2%, median aneurysm size 7 mm, 9 of 408 treated; 209 clipped +199 coiled [2]. Kuopio aneurysm data base 1977–2005 of 3005 patients with 4253 aneurysms there were 99 (10%) AChAA in 70 (8%) patients [3].

Paraclinoid aneurysm is defined as an aneurysm that originates at the internal carotid artery (ICA) distal to the proximal dural ring (PDR) and proximal to the posterior communicating artery (PCoA), which means both ophthalmic and clinoidal segments of the ICA. Patients with these aneurysms present with retro-orbital or supraorbital pain and varying degrees of visual field constriction and/or visual acuity decline which is associated with compression of optic nerve. This nerve is typically pushed superiorly and medially, which manifests as a unilateral inferomedial (lower nasal) quadrantanopsia [1]. In addition, paraclinoid aneurysms may manifest as progressive diplopia due to compression of the cranial nerves involved in ocular movement caused by aneurysm growth. Unruptured paraclinoid aneurysm has a low risk of rupture compared to other types of cerebral aneurysm. The surgical indications for unruptured paraclinoid aneurysm should consider this low rupture risk as well as several other factors such as the aneurysm shape, the aneurysm size, and how old the patient.

Anterior communicating artery (AComA) aneurysms are among the most common aneurysms in different case series. They compose 36 of 175 cases (20.6%) in our latest case series of unruptured aneurysms coming second only after middle cerebral artery aneurysms (69 cases) [1]. In case series of ruptured aneurysms, the incidence is higher, and around 30–40% of all intracranial aneurysms are located in the AcomA region. Their presentation with subarachnoid hemorrhage (SAH) is not essentially different from other aneurysms and will not be repeated in this chapter again. Here, we do not intend to make an exhaustive review of different aspects of medical, interventional, or surgical management of these aneurysms. Instead, we will explain the most important pre-, intra-, and postoperative aspects observed in our institute.

Middle cerebral artery (MCA) aneurysm is one of the most popular cerebral aneurysm. MCA aneurysm located in the superficial region of the brain and had relative wide neck, therefore it is usually selected to operate directly. The surgery of MCA aneurysm is basic and good case for young neurosurgeons. However, there are some tips and pitfalls in the surgery of MCA aneurysm. Preoperative simulation using 3D CT angiography is useful for avoiding the pitfalls. The preservation of veins reads good surgeons and preparation of premature rupture is necessary. We emphasize the importance of sharing the experience of surgery each other because the cases of surgery was decreasing recently.

This case illustration was a 62-year-old male presenting with the acute onset of worst headache of life symptoms (Hunt and Hess grade 2). Head computed tomography (CT) revealed Fisher grade 3 subarachnoid hemorrhage (SAH).

Aneurysms of the basilar artery (BA) may occur at several locations including the BA-vertebral artery junction, BA-anterior inferior cerebellar artery junction, BA-superior cerebellar artery junction, and BA tip. Upper BA aneurysm is usually considered to include BA tip aneurysm and BA-superior cerebellar artery junction aneurysm. BA aneurysm seldom manifests as neurological problems before rupture. Partially thrombosed BA aneurysm may manifest as progressive neurological deficits due to compression of the brain stem and cranial nerves caused by aneurysm growth. Unruptured BA tip aneurysm has a higher tendency to rupture compared to other types of cerebral aneurysm. Therefore, the surgical indications for unruptured BA aneurysm should consider this fact as well as the age, size, and shape of the aneurysm.

In a 57-year-old male, a persistent headache was evaluated by neurologists. MRI was done, and incidental superior cerebellar artery (SCA) aneurysm was discovered after assessment of abnormal image at the lateral aspect of the mesencephalon. CT-angio and angiography (Fig. 18.1) showed an aneurysm with saccular form at proximal portion of right SCA. Endovascular treatment was precluded by neuroradiologist due to the morphological characteristics of the aneurysm’s neck [1–3].

Posterior circulation aneurysms account for approximately 10% of all aneurysms, which affect 1–6% of the population [1, 2]. Aneurysms of the posterior inferior cerebellar artery (PICA) are very rare, only 0.5–3% of all aneurysms [3]. Patients with PICA aneurysms usually present with subarachnoid hemorrhage, or they might have symptoms due to compression of the brainstem or lower cranial nerves. Microsurgical clipping of PICA aneurysms is difficult and very challenging due to the limited working space and its surrounding neurovascular structure, the brainstem and lower cranial nerves IX, X, XI, and XII, and very often the aneurysm is located very deep and far from the surgeon’s view. Surgical maneuvers require moving around and sometimes in between cranial nerves. PICA aneurysms may vary widely within a range in terms of their complex anatomy, as a result either of their origin, branching out of the vertebral artery (VA), or their course along the lower cranial nerve. The PICA itself is usually of a small caliber, and aneurysms on it with a wide neck create a difficult situation with respect to clipping the aneurysm and preserving the PICA.

Aneurysm bigger than 25 mm is called giant aneurysm [1], further subdivided by morphology into saccular, fusiform, or dolichoectatic aneurysms [2]. Epidemiologically, they are very rare, comprising only 0.5% of all intracranial aneurysms, while others describe it as 3–5% of all intracranial aneurysms [1, 3, 4]; the epidemiology of intracranial aneurysms among the general population amounts to 0.2–9.9% [5]. In pediatric patients, the incidence of giant aneurysms and aneurysms of the posterior circulation is greater than those in adult patients [6]. The most common type is the saccular giant aneurysm, accounting for 98% of cases [7]. Fusiform types are more commonly found in the posterior circulation and MCA [1]. These lesions have a female preponderance and are diagnosed mostly between 40 and 60 years of age [2]. These lesions are found most often in the anterior circulation, affecting the ICA, MCA, and ACA [1, 2], while in the posterior circulation, they most commonly occur at the basilar artery, vertebrobasilar junction, PCA, and PICA [2]. Multiple giant aneurysms can be found in 7% of patients [2].