Intracranial aneurysms in children most commonly come to clinical attention following rupture, with associated subarachnoid hemorrhage (SAH) . A review of several patient series suggests that approximately 52–67 % of pediatric intracranial aneurysms are ruptured at diagnosis [5]. Ruptured aneurysm is believed to be the most common etiology of SAH among patients younger than 20 years. In a series of 167 children with proven subarachnoid hemorrhage, 52 % were found to have ruptured aneurysms , while 26 % had bleeding AVMs, and 19 % of cases were idiopathic [9]. The onset of subarachnoid hemorrhage is typically sudden, with headache, fever, vomiting, meningismus, cranial nerve palsy, seizure, paresis, deterioration in consciousness , and coma being common signs.

Enlargement of an unruptured aneurysm most commonly leads to cranial nerve findings related to the location of the aneurysm. Classically, anterior communicating artery aneurysms are associated with optic nerve findings, posterior communicating artery and basilar tip aneurysms with third nerve palsy, and posterior circulation aneurysms with lower cranial nerve palsies. Chronic nerve compression can also lead to unilateral papilledema ipsilateral to the aneurysm. Third nerve palsy manifests as ptosis and mydriasis (drooping eyelid and dry eye) and ophthalmoplegia (inability to move the eye vertically or medially). Lower cranial nerve palsies in children are most evident as difficulty swallowing and snoring or apnea at night.

While seizures are rarely associated with unruptured aneurysms , seizures do occur in 15–25 % of children with subarachnoid hemorrhage [5]. Seizures following subarachnoid hemorrhage are particularly dangerous in the cases of ruptured aneurysms . These seizures can cause dangerous increases in blood pressure that can precipitate rebleeding from the aneurysm, a major cause of morbidity and mortality. Therefore, anticonvulsants are used acutely for seizure management and prophylaxis. Seizures following subarachnoid hemorrhage rarely progress to epilepsy .

Intracranial aneurysms reach “giant” size (>2.5 cm) with much greater frequency in children than in adults. “Tumorlike presentation” is therefore significantly higher in early childhood (18.1 %) than in adulthood (2.5 %) [10]. Common presenting signs include lethargy, vomiting, and papilledema; infants may demonstrate a tense anterior fontanelle and splayed sutures. In the case of giant aneurysms , focal neurologic findings from mass effect may be due to the aneurysm itself. In approximately one-third of cases, hematoma was present at diagnosis [11].

Hydrocephalus often develops following aneurysmal subarachnoid hemorrhage. Subarachnoid and intraventricular blood impairs resorption of cerebrospinal fluid (CSF) at the arachnoid granulations, leading to hydrocephalus. In these cases, emergent surgical intervention may be necessary to divert the cerebrospinal fluid in order to control intracranial pressure; in the acute setting, a ventriculostomy may be performed emergently for placement of an external ventricular drain, both to monitor intracranial pressure and to divert CSF. Many children will never fully recover sufficient capacity to resorb CSF and may require permanent shunting to divert cerebrospinal fluid.

In the adult literature, cerebral vasospasm is well known to contribute significantly to morbidity and mortality following SAH. Case series data suggest, however, that in children vasospasm is not as significant a concern. While approximately 25 % of children develop severe angiographic vasospasm following aneurysmal subarachnoid hemorrhage and another 25 % develop mild radiographic vasospasm, no associated increase in morbidity or mortality has been shown in these children [5].

The autosomal dominant form of polycystic kidney disease (ADPKD) affects multiple organs including the heart, gastrointestinal tract, and kidneys. This form of the disease is associated with an increased risk of intracranial aneurysms , although a review of several series reveals that the observed prevalence of aneurysms in these patients varies from 0 to 41 % [5]. In 85 % of cases, adult polycystic kidney disease is attributable to a defect in the gene PKD1 on chromosome 16; the remaining 15 % of cases are attributable to a defect in PKD2 on chromosome 4. Both genes encode proteins with postulated roles in cell-cell matrix interactions and are thought to be relevant in vessel wall development [12].

Tuberous sclerosis (TS) is classically described as a developmental dysplasia affecting both ectodermal and mesodermal derivatives, and so the disease has manifestations in multiple organ systems, including the kidneys (renal cysts) and the brain (cortical tubers, subependymal nodules, subependymal giant cell astrocytomas, and intracranial aneurysms ). Clinically, it is associated with the triad of mental retardation, epilepsy, and adenoma sebaceum (red facial angiofibromas). The syndrome is known to be associated with mutations in two genes, TSC1 and TSC2, which encode the proteins hamartin and tuberin, respectively. The latter gene collocates on chromosome 16 with PKD1, explaining some of the associations with polycystic kidney disease. Tuberous sclerosis is thought to give rise to a congenital defect in the arterial wall, predisposing to the formation of multiple and fusiform (as opposed to saccular) intracranial aneurysms .

Coarctation of the aorta (narrowing at the insertion of the ligamentum arteriosum) is consistently reported to be associated with single or multiple intracranial aneurysms . The true strength of this association is difficult to estimate because the majority of intracranial aneurysms do not come to clinical attention until adulthood. However, one review of 200 patients with aortic coarctation reported only five patients (2.5 %) diagnosed in life with cerebral aneurysms [13].

Ehlers–Danlos refers to a group of disorders in collagen synthesis. The best known clinical manifestations of these syndromes are hyperelastic skin and hyperextensible joints. The classic phenotype is not present in Ehlers–Danlos type IV (defective type III collagen synthesis), which carries an association with intracranial aneurysm formation [14]. In Marfan syndrome, the genetic defect is in the FBN1 gene on chromosome 15, encoding a connective tissue matrix glycoprotein [15].

Histologically, pediatric intracranial aneurysms resemble their adult counterparts. Within the aneurysm, intima and smooth muscle are absent, and the wall of the aneurysm is formed only by the external elastic membrane. Saccular aneurysms form at arterial branch points, where shear forces are high. The walls of the cerebral vasculature are considerably thinner than those of systemic arteries; types I and III collagen predominate in these vessels. Detailed work by Stehbens has suggested that even in children, aneurysm formation may reflect a process involving hypertension, birth or in utero injury, and trauma [16].

Traumatic aneurysms are false or pseudoaneurysms, meaning there is disruption of the entire vessel wall. Rather than being contained by vascular tissue, the aneurysm has no true wall and is contained by surrounding neural structures—for this reason, they are friable, highly unstable lesions, and more prone to rupture than a true aneurysm [5, 17]. Traumatic aneurysms are more common in children due to their increased brain mobility and more fragile vessels. The presentation of traumatic aneurysms includes epistaxis, otorrhagia (bleeding from the ear), and cranial nerve palsy. These patients may also present with signs of hemorrhage with a history of trauma or penetrating injuries that could result in direct vessel injury. Cases presenting with epistaxis and otorrhagia are typically the result of carotid injuries associated with skull base fractures. To avoid operative morbidity and mortality, these lesions are commonly observed, with surgical or endovascular treatment reserved for cases demonstrating progressive enlargement. Overall morbidity and mortality from this condition is reportedly as high as 50 % [17].

The term “giant aneurysm” refers to a saccular aneurysm greater than 25 mm in maximal diameter. It is not known whether they expand dynamically, growing rapidly early in life from smaller initial lesions. It is known, however, that giant aneurysms make up a greater proportion of aneurysms seen in young children than they do in other age groups. While case series of intracranial aneurysms suggest that giant aneurysms represent 2–5 % of cases across all age groups, among children less than 5 years old, 30–50 % of aneurysms are giant.

Though still used in reference to infectious aneurysms , the term “mycotic,” introduced by Sir William Osler in 1885, is misleading as it suggests a fungal etiology. Most infectious aneurysms in children are associated with bacterial rather than fungal infections. The most common causative organisms in children are alpha Streptococcus, Staphylococcus, Pseudomonas, and Haemophilus species. Aneurysms attributable to fungal infections are rare, but when they do occur, typically in immunocompromised patients, Aspergillus and Candida are the organisms most frequently responsible.

Infectious aneurysms may be classified into three primary types [18]. The first type is most common and occurs in the setting of bacterial endocarditis with subsequent embolization to the intracranial circulation. The second type involves direct extension from an adjacent infectious source, as may occur in meningitis, osteomyelitis, or sinusitis. The third type of infectious aneurysm is isolated to the intracranial circulation, with no identifiable source elsewhere in the body.

Surgical treatment is not typically indicated for these lesions, both for technical reasons and because they commonly stabilize and regress with medical therapy alone. Antibiotic therapy for 4–6 weeks should be initiated, with serial imaging at 3, 6, and 12 months. Typically, surgical treatment is indicated only in the setting of aneurysmal rupture or progression despite appropriate antibiotic therapy.

The natural history of asymptomatic, unruptured intracranial aneurysms is a subject of ongoing interest to investigators and has been addressed in a number of large longitudinal studies over the past several decades [23]. There is general agreement that no intervention is indicated for such aneurysms when the diameter is <7 mm and that these lesions may be safely observed with interval MRI; intervention may be considered for symptomatic, large, or expanding lesions.

The estimated immediate mortality after aneurysmal subarachnoid hemorrhage is approximately 10–20 % in children, as compared with 20–30 % in adults. Estimates of overall mortality range from 13 to 34 % in the literature [5], as compared with approximately 45 % in adults [24].

Definitive treatment of a ruptured intracranial aneurysm is obliteration of the aneurysm through microsurgical or endovascular treatment. In children, evidence suggests that surgical or endovascular treatment should almost always be attempted, as intervention consistently yields better outcomes than medical management alone [5]. Emergent referral to a center with a neurosurgeon on staff should be a priority in cases of suspected aneurysmal rupture.

Cavernous malformations, also known as cavernomas, cavernous angiomas, or cavernous hemangiomas, are abnormal collections of dilated blood vessels that can be found throughout the central nervous system. These lesions do not contain normal brain parenchyma. They are low-flow, dynamic lesions and may therefore appear spontaneously and change in size over time.

There are two principal varieties of cavernous malformation: sporadic and familial. Familial lesions tend to appear at younger ages, more commonly present with multiple lesions, and carry an overall higher risk of hemorrhage [5, 7, 17]. The familial form appears to be inherited in an autosomal dominant manner with variable penetrance [5, 7, 17]. However, no clear guidelines currently exist regarding the screening of patients with strong family history of cavernous malformations , as is further discussed below.

Cavernous malformations have been estimated to be present in approximately 0.4–0.8 % of the population [7], and approximately 25 % of these lesions affect children [5, 7, 17]. No significant difference in prevalence between genders has been noted [7]. Several studies have commented on a bimodal distribution of ages at presentation with patients between 1–3 and 11–16 years having higher incidence of symptomatic lesions [7]. Rarely, however, are lesions clinically evident before 1 year of age [7]. Cranial irradiation has been noted in several studies to be a risk factor for development of cavernous malformations [7, 17]. The average time from radiation to detection of these lesions is approximately 9 years [14], and they appear more prone to hemorrhage than sporadic cavernous malformations (Fig. 23.2).

Reports have indicated that up to 40 % of cavernous malformations are asymptomatic [17]. Since children are less likely to undergo neuroimaging, the reported proportions of lesions that are clinically silent may be underestimated, as many of them may go undetected. Only 14.2 % of childhood cavernous malformations are detected incidentally [7].

Seizure is the most common presenting symptom for patients with symptomatic cavernous malformations . Such seizures may be partial or generalized and are the presenting symptoms in up to 70 % of cases [5]. Other signs and symptoms of cavernous malformation are related to hemorrhage, including signs of increased intracranial pressure and acute onset neurological deficits [7, 14, 17]. Importantly, cavernous malformations in children are approximately two to three times more likely to present with hemorrhage than corresponding lesions in adults [7, 14, 21], and cavernomas found in children tend to be larger than those in adults [7].

MRI is the most important diagnostic study for cavernous malformations . The sensitivity and specificity of MRI are superior to CT [7, 14, 17], and the findings of these lesions on MRI are so distinct as to be pathognomonic for cavernous malformation [7]. The classic MRI findings of cavernous malformations are a reticulated core of mixed signal intensity with a rim of decreased signal intensity on a T2-weighted series [23]. The sensitivity and specificity of CT are inferior to MRI for detecting cavernous malformations [23], but CT does readily detect acute hemorrhage and may lead to the acquisition of more correct or specific investigations [7].

Cavernous malformations are dilated vascular spaces lined by a single layer of endothelial cells [17, 23]. Typically, these spaces do not have smooth muscle or elastin [17]; histologically, cavernous malformations do not resemble capillaries, arteries, or veins [17, 23]. No normal intervening neural tissue is contained in these lesions [7, 17, 21, 24]. Neural tissue surrounding cavernous malformations shows accumulation of hemosiderin-laden macrophages, reactive gliosis, and deposits of lead and calcium [17]. The mechanisms causing cavernous malformations are unclear, although some have suggested disrupted cerebral hemodynamics, due to the presence of developmental venous anomalies [25, 26].

The vast majority of patients with diagnosed cavernous malformations should be referred for neurosurgical evaluation. The largest question is whether these evaluations need to be made on an emergent basis. Clearly, patients with evidence of acute hemorrhage should be emergently referred to the care of a neurosurgeon. For clinically stable patients without evidence of hemorrhage, the referral is less urgent, but all symptomatic patients should have a neurosurgical consultation.

As previously stated, there are no clear guidelines regarding whom to screen or when to screen in cases of strongly suspected or genetically confirmed familial cavernous malformations . It is well recognized that the familial form of the disease produces highly dynamic lesions, with de novo cavernoma formation a common event over the natural history of these patients [27, 28]. If a patient is screened, MRI is certainly the modality of choice; however, it is not clear that MRI screening of asymptomatic family members of those with confirmed or suspected familial cavernous malformations can improve outcomes .

It is generally agreed that asymptomatic cavernous malformations should be treated conservatively and observed for clinical signs of hemorrhage and with serial imaging studies to assess for lesion progression [7, 14, 17]. This is particularly true for cavernomas located in eloquent cortex or in the brain stem or other locations difficult to access surgically [7].

For symptomatic cavernous malformations , the total surgical excision is the treatment of choice [7, 14, 17, 24]. Complete excision of the lesion eliminates the risk of bleeding from remnant lesion, which may occur in up to 25 % of subtotal excisions [7]. Results of surgical series have shown drastic improvement in seizure control of patients with seizures referable to the cavernous malformation [5, 7]. Early removal of cavernous malformations causing seizures can be curative [5, 7], and as a result, more patients are having early surgical excision of these cavernomas [7]. Surgery is also the recommended management strategy for cavernous malformations causing hemorrhage or worsening neurological deficits [7, 14].

Radiosurgery has been suggested as an alternative to surgery for cavernous malformations located in surgically inaccessible areas. The results obtained through radiosurgery have not consistently demonstrated a significant improvement over the natural history of these cavernous malformations [7, 14]; radiosurgery is not currently a recommended treatment strategy for pediatric cavernous malformations.

The annual risk of hemorrhage from cavernous malformations inclusive of all age groups is approximately 1.6 % per year [29]. Cavernoma hemorrhage appears to produce less harm and presents more insidiously than hemorrhage from higher flow lesions such as arteriovenous malformations [17]. However, these lesions may rebleed and produce recurrent seizures or progressive neurologic deficits [7, 17]. Surgical treatment tends to produce good outcomes in children—preventing subsequent hemorrhage and curing or significantly reducing the frequency of seizures [7, 17]; the surgical treatment of brain stem lesions is less straightforward, as resection has a higher probability of temporary or permanent neurological deficits [30, 31].

Cerebral venous malformations, also referred to as venous angiomas or developmental venous anomalies, are benign congenital anomalies of the venous circulation. These lesions consist of an area of anomalous veins draining into a larger trunk. Depending on location, this trunk may drain into the superficial or deep cerebral venous system. These anomalous veins are intertwined with otherwise normal brain parenchyma, and there are no associated anomalous arterial vessels. Although they are developmental venous anomalies, these venous malformations provide venous drainage to normal brain tissue.

Venous malformations constitute the most common form of intracerebral vascular lesion, with a population prevalence of approximately 3 % [25]. The risk of spontaneous intracranial hemorrhage from a venous angioma is very low, with annual hemorrhage rates of between 0.15 and 0.34 % per patient per year confirmed in several natural history studies [25].

Venous malformations are most commonly asymptomatic. They are found in association with cavernous malformations and may be discovered incidentally during the workup of symptoms related to the cavernous malformation. In rare cases, venous malformations will produce symptoms, most commonly seizures or hemorrhage. It is very important to bear in mind, however, that intracranial hemorrhage in patients with cerebral venous malformations is not typically due to the venous malformation; instead, it is more commonly due to a more pernicious, coexisting lesion, such as a cavernous malformation.

Venous malformations may be diagnosed incidentally on CT or MR imaging or on cerebral angiograms performed for other indications. They appear on contrast-enhanced CT as linear enhancing structures in the hemispheric white matter. On MRI, they are classically described as producing contrast-enhancing “stellate flow voids” that extend toward the ventricles. Angiography usually demonstrates a prominent vein passing through the white matter, ending in a “caput medusae” of draining veins.

When a patient presents with new neurologic symptoms and is found to have a venous malformation, alternate explanations for the symptoms should still be sought; venous angiomas should be regarded as incidental in patients with recurrent headache and certain other symptoms [32].

Cerebral venous malformations are thought to arise as aberrations in regional vein development, as brain parenchyma in the vicinity of these lesions tends to be poor in normal-appearing veins. The classic “caput medusae” appearance of venous angiomas on angiogram is due to the configuration of dilated medullary veins running through normal brain parenchyma and arranged around venous channels into which they drain. Again, venous angiomas function as a component of the cerebral arteriovenous network, draining the normal brain parenchyma incorporated by these lesions .

Many patients with cerebral venous malformation may already have been referred to a neurosurgeon at the time of diagnosis due to the association of these lesions with other vascular malformations, particularly cavernous malformations . Incidental discovery of an asymptomatic venous malformation does not warrant neurosurgical referral. However, decisions regarding treatment for venous malformations that are thought to be symptomatic should include a neurosurgeon.

Given the low risk of spontaneous intracranial hemorrhage and their role in cerebral venous drainage, cerebral venous malformations are typically managed conservatively.

Radiation is not typically advised, as this modality carries a high risk of complications (in approximately 30 % of patients) and may not completely obliterate a venous malformation.

It is very important to recognize that these lesions drain normal areas of the brain. Therefore, excisional surgery eliminates venous drainage from a region of normal brain and may result in venous infarction and cerebral edema. For this reason, surgical excision is not typically pursued in asymptomatic cases.

An arteriovenous malformation (AVM) is a vascular malformation in which arterial circulation flows directly into the venous drainage system without an intervening capillary bed. The center of such a lesion, where there is a transition from the arterial to the venous system, is known as the nidus and contains no neural parenchyma. The fundamental danger of these lesions arises from the feeding of the high-flow, high-pressure arterial system into the low-pressure venous system; these configurations establish the potential for a pressure-flow mismatch that overcomes the strength of the vascular wall, resulting in vascular rupture and hemorrhage.