Introduction

Paediatric aneurysms are rare, accounting for 2% to 6% of all aneurysms and have distinct characteristics from the aneurysms found in adult population [1–4]. In children, aneurysms have a male predominance and are more commonly located in the carotid bifurcation and posterior circulation, there is a higher incidence of large and giant aneurysms and spontaneous thrombosis of aneurysms is more common [1–11]. In more than half of the paediatric aneurysms there is an underlying disorder predisposing to aneurismal formation such as infection, trauma, tumour or dissection [1–11].

Paediatric arterial dissections account for 7% of all dissections [12] but represent an important cause of ischaemic stroke in this age group, being the most frequent cause of stroke in the posterior circulation [13]. The most common arterial dissection location in children is the carotid artery territory in which they are more frequently intradural, and mostly located in the supraclinoid internal carotid artery (ICA) and middle cerebral artery (MCA). [12, 14, 15]. In contrast, posterior circulation dissections are rarely intracranial, being reported in only 4% of cases [14]. Subarachnoid haemorrhage is a rare mode of presentation for dissections in children, accounting for less than 2% of cases [14].

Spontaneous dissections have been rarely reported as a cause of posterior cerebral artery (PCA) aneurysms in the paediatric population [4, 14, 16]. We report here two cases of paediatric spontaneous dissecting aneurysm, including the documentation of aneurysm development, and review the literature on posterior cerebral dissecting aneurysms in this age group.

Case report

Patient 1

After a regular night's sleep, this 33-month-old male child wakened with a sudden and strong headache followed by vomiting and loss of consciousness. The child had been otherwise healthy and there was no history of previous trauma. There was no family history of congenital neurological or vascular disease.

During transportation to the hospital, the patient had two generalized seizures and was medicated with two 5 mg diazepam suppositories. He was admitted to the emergency department and on examination he was only responsive to pain stimulation, localizing the pain, had anisocoria with right dilated pupil, right flaccid hemiparesis and irregular ventilation with periods of inspiratory pauses. The patient was sedated and kept on anticonvulsive therapy and ventilation.

The CT performed showed diffuse subarachnoidal and intraventricular haemorrhage with acute hydrocephalus. The patient was taken immediately to the operating room and a ventricular shunt was placed. Afterwards, an angio-CT was done showing a left posterior P2 cerebral aneurysm. During the hospitalization the patient recovered gradually, was extubated on day 6, and remained only with a mild right hemiparesis (grade 2).

The patient had been admitted to a different hospital from ours and was referred to us after clinical stabilization.

We scheduled the patient for immediate embolization that was performed under general anaesthesia and full heparinization. A 5F sheath was placed on the right femoral artery and a 5F guiding catheter was advanced. The diagnostic cerebral angiogram revealed a dissecting P2 aneurysm with a proximal stenosis and aneurysmal contrast agent stagnation (Fig. 1). The posterior communicating arteries were prominent and filled the PCA territories. The guiding catheter was placed in the proximal V2 left vertebral artery segment and a microcatheter was advanced into the left PCA P2 segment. Two bare coils (2D 3×4 mm and 2×2 mm) were placed in the aneurysm and parent artery covering the stenotic segment, achieving P2 PCA occlusion proximal to the stenosis. The control angiogram confirmed the PCA occlusion with neither antegrade nor retrograde aneurysmal filling (Fig. 2). The carotid angiogram showed the opening of leptomeningeal MCA–PCA anastomosis filling the distal PCA territory.

Fig. 1
figure 1

Digital subtraction angiography: left vertebral angiogram late arterial phase reveals a dissecting P2 aneurysm with contrast agent stagnation inside. Note the presence of a normal arterial variation of the left vertebral artery: intradural duplication of the vertebral artery at C1–C2

Full size image
Fig. 2
figure 2

Post-treatment (embolization) control angiogram confirming the PCA occlusion and aneurysm exclusion

Full size image

The patient tolerated the procedure well and there were no new clinical deficits, including visual field defect. MRI/MRA performed 3 days after the procedure showed the thrombosis of the aneurysmal sac and the absence of a PCA territory infarct.

The final follow-up MRI/MRA was performed 18 months after the treatment and confirmed the disappearance of the aneurysm and the presence of excellent collateral arterial circulation.

Patient 2

This 9-year-old boy had been followed since the age of 11 months in a paediatric neurology clinic for developmental delay and epilepsy. Except for the age of the mother (41 years), the pregnancy and birth were uneventfully. There was no family history of neurological or vascular diseases and the child had a healthy older brother. The initial clinical and laboratory search for metabolic and genetic disorders was negative. The patient was under anticonvulsive therapy (sodium valproate) and had sporadic seizures.

An MRI performed at the age of 7 years was normal (Fig. 3). Although, the patient had been clinically stable, with moderate developmental delay and sporadic seizures, an MRI was repeated at the age of 9 years. This MRI/MRA depicted a partially thrombosed aneurysm of the right PCA P2 segment (Fig. 4) neither related with a branching point nor having a saccular appearance, suggestive of a spontaneous dissecting aneurysm. There was no recent history of trauma, seizures or any modification of the patient’s clinical status.

Fig. 3
figure 3

Sagittal T1-W SE MR image showing a normal-appearing quadrigeminal cistern and neighbouring brain structures

Full size image
Fig. 4
figure 4

a, b Sagittal T1-W SE (a) and axial PD FSE (b) MR images reveal the development of PCA aneurysm. c MRA 3D TOF, MIP axial reconstruction shows the distal PCA (P2 segment) aneurysm with a focal proximal arterial narrowing (open arrow)

Full size image

The patient was referred to our endovascular clinic and scheduled for elective diagnostic angiography and embolization.

In the intervening time, there was a gradual change in the patient’s clinical status, characterized by sleepiness, gait disturbance, headache and, finally, vomiting. The child was taken to our emergency department and on examination he was somnolent but responded to verbal orders, had bilateral papilloedema and gait disequilibrium. The CT performed on admission showed acute hydrocephalus caused by quadrigeminal plate compression caused by an enlarged, spontaneously hyperdense (thrombosed) aneurysm, with no signs of intracranial haemorrhage. The patient was taken immediately to the operating room to place a ventricular shunt. The MRI confirmed the quadrigeminal plate compression by the enlarged thrombosed aneurysm (Fig. 5) and the absence of ischaemic infarct on the PCA territory. The patient was submitted to a diagnostic angiogram that confirmed the total spontaneous thrombosis of the dissecting aneurysm with PCA occlusion just proximal to the aneurysm (Fig. 6). It also showed the presence of good collateral circulation through leptomeningeal PCA–MCA anastomosis. The patient gradually recovered to his premorbid clinical status and was discharged 2 weeks after admission.

Fig. 5
figure 5

Sagittal T1-W SE MR image reveals spontaneous thrombosis of the PCA aneurysm that caused aneurysmal enlargement, compression of the tectal plate and acute hydrocephalus

Full size image
Fig. 6
figure 6

Digital subtraction angiography: left vertebral angiogram late arterial phase reveals the spontaneous thrombosis of the PCA aneurysm associated with thrombosis of the parent artery just proximal to the aneurysm

Full size image

The patient was followed clinically without any interval changes and by imaging. An angiogram acquired 2 months after the first angiogram showed the stability of the aneurysmal spontaneous thrombosis and a final follow-up study ay 18 months was done by MRI/MRA and confirmed the disappearance of the aneurysm and the absence of hydrocephalus and brain lesions.

Discussion

Intracranial dissecting aneurysms have been reported with increasing frequency in recent years probably due to a higher awareness of the disease and to more accurate diagnostic imaging methods. However, the diagnosis of intracranial arterial dissection is still often difficult and the imaging signs are subtle. The most common angiographic signs are the “pearl and string” sign, meaning an aneurysmal dilation preceding or following a stenosis, the “string” sign, signifying an arterial stenosis or occlusion, and the fusiform or saccular aneurysmal dilation with stagnation of contrast agent inside [17–21]. Other less common signs include the double lumen and the intimal flap [17–21]. Repeated follow-up angiography may show different imaging signs, due to the fast morphological evolution of these lesions [21]. In adults it may be difficult to distinguish an arterial dissection from an atherosclerotic lesion [17, 20, 22] or from a saccular aneurysm with concomitant vasospasm, which is generally diffuse and delayed in onset after the bleeding [20, 23]. Moreover, the differentiation between intraluminal and mural thrombosis based only on imaging methods may be also troublesome. Nonetheless, whenever there is an aneurysm associated with proximal or distal parent vessel stenosis and/or with stagnation of contrast agent inside, the diagnosis of dissecting aneurysm should be considered [24].

In series of paediatric aneurysms reported by Patel and Richardson [7], Amacher et al. [25] and Storrs et al. [26], there is no mention of spontaneous dissecting aneurysms, in contrast to traumatic aneurysms that have always been a frequently recognized type of aneurysm in children. In more recent series, spontaneous dissection as been inconsistently pointed out as a cause of paediatric aneurysms. Allison et al. [11], in 1998, reviewing a series of patients over a period of 20 years, made no mention of spontaneous dissecting aneurysms. In a paediatric aneurysm series from the Hospital for Sick Children in Toronto [16] there was at least one dissecting aneurysm and, more recently, in a paediatric aneurysm series from the Bicêtre Hospital in Paris spontaneous intradural dissecting aneurysms accounted for up to 45% of all paediatric aneurysms. However, in the latter series a more broad definition of dissecting aneurysms was used including not only acute but also subacute and chronic dissecting aneurysms such as fusiform aneurysms and partially thrombosed aneurysms [4].

In general, PCA aneurysms are rare, accounting for 0.8–1.4% of all aneurysms [9, 27, 28], and 12% of these aneurysms occur in the paediatric age group [27]. Indeed, if one considers that the underlying aetiology of PCA fusiform aneurysms may be the same as that proposed for spontaneous fusiform MCA aneurysms and they may therefore correspond to chronic dissecting lesions [4, 29], some of these reported PCA aneurysms [27, 28, 30–32] may have corresponded to dissecting aneurysms. Paediatric spontaneous dissecting PCA aneurysms are extremely rare, being less commonly described than traumatic dissecting aneurysms, and, to the best of our knowledge, there are only three case reports of spontaneous dissecting PCA aneurysms in the literature [4, 14, 16], two presenting with subarachnoid haemorrhage [4, 14] and one with ischaemic stroke [16].

Vertebrobasilar dissections are more frequently extracranial [12, 14, 21, 27–35]. The intradural dissections more commonly affect the vertebral or the basilar arteries that are also the most common locations for dissecting aneurysms of the posterior circulation [12, 14, 21, 27–35]. Trauma is the most common predisposing factor to extracranial and intracranial dissecting aneurysms in the vertebrobasilar territory [8, 21, 36, 37].

The natural history of intracranial dissections remains poorly understood. The dynamic nature of this disease, reflecting injury and healing processes during a period of time that may last for several months after the initial insult, may lead to distinct outcomes. The cases reported here illustrate two different evolutions of similar PCA aneurysms: spontaneous thrombosis and haemorrhage. Spontaneous disappearance of aneurysms is common in children and its occurrence is unpredictable [1, 2, 4]. It is estimated to occur in 1–2% of saccular aneurysms [38–43], more commonly in large or giant aneurysms [44], being associated with complete thrombosis of the parent vessel in up to 38% of cases [38, 40, 44]. Spontaneous thrombosis has also been reported in traumatic [45, 46] and in dissecting aneurysms [4, 23, 40, 44, 47–49]. In paediatric dissecting aneurysms spontaneous thrombosis is not uncommon and it may occur in up to 28% of cases [4]. The mechanisms responsible for spontaneous thrombosis and the imaging features that could point to such evolution remain obscure. A high ratio of aneurysm sac volume to neck size may be the cause of a low aneurysmal blood inflow that may promote the spontaneous thrombosis of aneurysms [50]. The associated proximal parent artery stenosis, that reduces the inflow and causes blood stagnation inside the aneurysm, may facilitate aneurysmal thrombosis. The dissection progression/recurrence causing proximal artery occlusion or parent artery compression by enlarging the aneurysm can also be responsible for spontaneous thrombosis of dissecting aneurysms.

Ruptured intracranial dissections carry an ominous prognosis and warrant early active treatment. In the paediatric population dissecting aneurysms have a worse prognosis than saccular aneurysms [4]. Dissecting aneurysms have an extremely high rebleeding rate, estimated to be in the range 30–58%, occurring during the acute phase, mostly in the first 24 h, with an associated high mortality rate [24, 51–56]. In contrast, unruptured intracranial dissections have a high recovery potential, including the possibility for spontaneous resolution [20, 23, 38, 39, 57], and can be managed conservatively, the exceptions being the presence of a large symptomatic aneurysmal dilation, aneurysmal enlargement in the follow up studies, and progression of the dissection [20, 23, 38, 39, 57].

There is no evidence that paediatric intracranial dissections will behave differently from those in adults. For unruptured lesions, conservative measures include bed rest and blood pressure control [19]. Antiplatelet or anticoagulant therapy is controversial and may be offered to patients harbouring unruptured stenotic or occlusive lesions without aneurysmal dilation [22]. Although still controversial, conservative treatment has also been advocated for stenotic ruptured intracranial dissections without aneurysmal dilation or the “pearl and string” sign since a significant number of these cases, up to 44%, have a favourable outcome under conservative treatment [56].

Endovascular treatment is a valuable treatment option for intracranial dissecting aneurysms [17] with lower mortality and morbidity than surgery [19, 56]. Intracranial dissecting aneurysms have been treated by parent vessel occlusion and by aneurysmal coiling with or without stent placement [17]. Distal PCA aneurysm surgery has had distinct reported outcomes [33, 58], but is generally associated with high surgical risk [19, 53, 58–65], and the endovascular approach has been suggested for these surgically challenging cases [66]. Some authors have reported successful PCA dissecting aneurysmal embolization with coiling of the aneurysmal false sac and preservation of the parent artery [37]. We have generally favoured an urgent endovascular deconstructive approach, in view of the fact that the wall of these aneurysms is weak and may easily rupture during coiling. We occlude the PCA with endovascular coil deposition at the lesion, avoiding packing the dissecting aneurysm sac, and just proximal to the aneurysm in order to prevent incomplete thrombosis of the aneurysm. However, if there is significant associated arterial vasospasm we delay the treatment and if there is a known underlying arterial disease predisposing for arterial dissection and recurrence, the management should favour a constructive approach.

There are some anatomic considerations that may predict the probability of neurological deficit after a deconstructive approach to PCA aneurysms. A balloon occlusion tolerance test is the best method to access the outcome of parent vessel occlusion. However, in children this clinical evaluation is not feasible and the physiological evaluation, such as EEG monitoring, may not be entirely reliable. Therefore, a correct anatomic analysis may allow the risk estimation according to the segment of PCA occlusion. The neurological deficit after PCA surgical and endovascular occlusion ranges from 0% to 17% [37, 67–70]. It is important to differentiate the deficit resulting from occlusion of the perforators from that ensuing from the reduced antegrade PCA blood flow. Generally, providing that great care is taken to preserve the central perforator branches, namely those that irrigate the thalamus and midbrain, PCA occlusion beyond the origin of the posterior (inferior) temporal branch is associated with a low morbidity rate [37, 47, 67–71]. According to the anatomic PCA division of Zeal and Rhoton [72], from the P2a segment originate the thalamogeniculate and hippocampal arteries and from the P2b segment arise the medial anterior and lateral posterior choroidal arteries. Distal to these segments, there is a rich cortical leptomeningeal anastomosis between the splenial artery and the posterior pericallosal branch of the anterior cerebral artery, and between the inferior temporal artery and the superior temporal branches of the MCA. These anastomoses may overcome the proximal PCA occlusion. These anastomoses are expected to be well functioning in children without an underlying occlusive vasculopathy.

Finally, there are anecdotal reports of recanalization of thrombosed aneurysms [73–78] and of rebleeding after proximal artery occlusion [19, 60] indicating that there is a need for follow-up studies to ensure definitive aneurysmal thrombosis.

Conclusions

Spontaneous arterial dissection is a rare, probably still under recognized, cause of intracranial aneurysms. Dissecting aneurysms may be responsible for a significant number of the spontaneous aneurysmal thrombosis in children. Dissecting aneurysms are dynamic lesions with variable and unpredictable evolution and close follow-up and/or early treatment is warranted. The natural history in children needs to be further elucidated but according to the present knowledge, these lesions should be managed in the same manner as dissecting aneurysms in adults.