MAMC Journal of Medical Sciences

REVIEW ARTICLE
Year
: 2021  |  Volume : 7  |  Issue : 3  |  Page : 187--203

Neuroimaging of Pediatric Brain Tumors − A Review


Harish C Sneha, Sapna Singh, Rashmi Dixit, Anjali Prakash 
 Department of Radiodiagnosis, Maulana Azad Medical College & Lok Nayak Hospital, New Delhi, India

Correspondence Address:
Harish C Sneha
Department of Radiodiagnosis, Maulana Azad Medical College & Lok Nayak Hospital, New Delhi-110002
India

Abstract

Brain tumors are the second most common malignancy and the most common solid tumors in the pediatric population. Most brain tumors in the pediatric population are primary in origin contrary to the adult population. The various factors useful for establishing the diagnosis include the age of the patient, imaging characteristics, and location of the tumor. Infratentorial tumors are more common between 4 and 10 years of age, whereas supratentorial tumors are common in neonates and infants up to 3 years. Conventional computed tomography and magnetic resonance imaging are of paramount importance in the diagnostic evaluation of these tumors which help in their characterization and allow accurate assessment of their extent. The updated World Health Organization classification of brain tumors has incorporated various genetic and molecular parameters. It is essential for the radiologists to be familiar with the imaging features of genetic tumor subtypes as it plays a role in patient management and prognostication. Advanced neuroimaging provides additional information regarding the metabolism and physiology of these lesions, thereby aiding in their diagnosis and follow-up.



How to cite this article:
Sneha HC, Singh S, Dixit R, Prakash A. Neuroimaging of Pediatric Brain Tumors − A Review.MAMC J Med Sci 2021;7:187-203


How to cite this URL:
Sneha HC, Singh S, Dixit R, Prakash A. Neuroimaging of Pediatric Brain Tumors − A Review. MAMC J Med Sci [serial online] 2021 [cited 2022 Aug 19 ];7:187-203
Available from: https://www.mamcjms.in/text.asp?2021/7/3/187/328060


Full Text



 Introduction



Brain tumors are the most common cause of cancer-related mortality in the pediatric population.[1] The incidence of childhood central nervous system (CNS) tumors in the urban Indian population has been found to be 10 to 20 per million children, per year.[2] The risk of malignancy seems to be higher in younger children.[3] Common tumors in the neonatal period include teratomas and tumors of embryonal origin. The supratentorial tumors include astrocytomas, dysembryoplastic neuroepithelial tumor (DNET), and desmoplastic infantile gangliogliomas (GGs).[4] Infratentorial tumors include pilocytic astrocytomas, medulloblastomas, and ependymomas.

The pathogenesis of most pediatric brain tumors is not well known. An association with certain genetic syndromes, such as neurofibromatosis types 1 and 2 (NF-1 and NF-2), Turcot syndrome, Li–Fraumeni syndrome, Gorlin syndrome has been established. Radiation exposure has also been found to increase the risk of brain tumors.[1]

Clinical presentation depends on the location of the tumors in the CNS and age of the patient. They vary from macrocephaly, irritability, loss of developmental milestones in infants to neurologic deficits, and symptoms of increased intracranial pressure including headache, nausea, vomiting, and altered mental status in older children.[1] They can also present with seizures, behavioral changes, difficulty in speech, cerebellar signs, decreased vision, and other cranial nerve abnormalities depending on the location of the tumor.

Classification

The World Health Organization (WHO) classification of brain tumors was updated in 2016 and the nomenclature of various previously recognized tumors, such as gliomatosis cerebri, primitive neuroectodermal tumors, and oligoastrocytoma have been redefined or eliminated. On the other hand, multiple new entities have been described, including multinodular and vacuolating tumor of the cerebrum, diffuse leptomeningeal glioneuronal tumor, and so on. The latest classification incorporates several molecular and genetic factors in addition to the traditional histological parameters as these factors have been found to contribute significantly to patient care and prognosis. It is possible to identify some of these molecular subtypes based on imaging. Hence, it is essential for radiologists to be familiar with the characteristic imaging patterns that correlate with the particular disease subtypes.[5]

Embryonal tumors

The term primitive neuroectodermal tumor has been excluded from the lexicon in the recent brain tumor classification. Instead, the tumor entities in this group are addressed by their individual names such as medulloblastoma, atypical teratoid rhabdoid tumors (ATRTs), and so on.[5]

Medulloblastomas

These are high-grade tumors of embryonal origin and the most common malignant brain tumors in the pediatric population.[1] They are usually diagnosed before 15 years of age and have a male predominance. Uncommonly they can be seen in adults in the third and fourth decades of life. They usually occur in the midline involving the vermis. However, certain adult variants tend to occur in the cerebellar hemispheres.

In the 2007 WHO classification, medulloblastoma was divided into four histologic variants, including classical, anaplastic/large-cell variant, desmoplastic/nodular, and medulloblastoma with extensive nodularity. The 2016 classification has incorporated both histological and molecular findings and the tumor has been divided into: wingless (WNT), Sonic hedgehog (SHH), group 3, and group 4.[1]

WNT medulloblastoma: This is the subtype with the most favorable prognosis and accounts for approximately 10% of medulloblastomas. They usually occur in children older than 3 years and both sexes are equally affected. These tumors are usually off-midline, seen as cerebellopontine angle masses.[6]

SHH medulloblastoma: This subtype is seen in approximately 30% of medulloblastomas. It has a better prognosis compared with group 3 tumors. This is the most common subtype seen in the adult population. Recently, these tumors have been further divided into SHHα, SHHβ, SHHγ, and SHHΔ medulloblastomas. These tumors are located laterally in the cerebellar hemispheres [Figure 1] with vermis being the next most common location.[6]{Figure 1}

Group 3 medulloblastoma: These are usually midline in location, affect infants and children with a male predilection. Almost 50% patients have metastasis at presentation [Figure 2]. It has been further divided into three subtypes namely α, β, and γ.[6]{Figure 2}

Group 4 medulloblastoma: This is the most common subtype comprising of nearly 40% of all medulloblastomas with an intermediate level of prognosis. These are seen predominantly in children with a male predilection. On imaging, these are seen as midline tumors involving the vermis and fourth ventricle showing minimal or no enhancement [Figure 3].[6]{Figure 3}

Imaging: Medulloblastomas typically appear as relatively well-defined midline lesions involving the fourth ventricle. In keeping with their high cellularity, they typically appear hyperdense on noncontrast computed tomography (NCCT) scan. On postcontrast scans, they show moderate to intense homogenous enhancement. Cystic changes and necrosis are less common with hemorrhage being rare. Calcification is seen in approximately 20% cases.

On magnetic resonance imaging (MRI), they appear hypo-isointense on T1 weighted image (T1WI) and T2 weighted image (T2WI). Presence of hemorrhage, calcification, and necrosis are responsible for signal heterogeneity. They often show restricted diffusion on DWI. Moderate to strong enhancement is seen on post-contrast scans. On magnetic resonance spectroscopy (MRS), they show elevated choline, taurine, and lipid levels and low N-acetyl aspartate peaks. However, SHH medulloblastomas have been found to have low or absent taurine peak.[6]

Atypical teratoid/rhabdoid tumors

These are highly aggressive WHO grade IV tumors which frequently demonstrate biallelic inactivation of SMARCB1 gene on chromosome 22.[6] Histologically, they have varying proportions of mesenchymal, epithelial, glial, and neuronal elements. These are seen in children under 3 years of age with a moderate male predominance. An association with rhabdoid tumors of the kidney is known.[3] ATRTs can occur in both supra- and infratentorial location with almost equal frequency involving the cerebral and the cerebellar hemispheres, respectively. In contrast to medulloblastomas, ATRTs occur in a younger age group, tend to involve the cerebellopontine angle, and often show hemorrhage.[7]

Imaging: On NCCT, they appear hyperdense with areas of cystic changes, hemorrhage, and calcification. Tumors are usually large with marked perilesional edema and cause mass effect on surrounding structures leading to hydrocephalus when seen in the posterior fossa. They show strong heterogenous contrast enhancement.

On MRI, they are iso-hypointense on T1W1 and so-hypointense on T2WI, and show restricted diffusion on DWI with areas of blooming on GRE/SWI sequences corresponding to foci of hemorrhage or calcification. Heterogenous postcontrast enhancement is noted [Figure 4]. On magnetic resonance spectroscopy (MRS), elevated choline peak can be seen with decreased or absent N-Acetyl aspartate (NAA) peak. Leptomeningeal spread of the tumor is very common.{Figure 4}

Embryonal tumor with multilayered rosettes (ETMR)

This is a recently described tumor in children less than 4 years of age, usually affecting infants with a very poor prognosis. Histologically these tumors show small, blue, tumor cells forming multilayered rosettes in a background of neoplastic neuropils. If the characteristic genetic alteration, that is, if C19MC alteration is present, they are called ETMR-C19MC altered and if these alterations are absent, they are referred to as C19MC-NOS.[5] More than 70% are located in the cerebrum with the remaining involving the brainstem or cerebellum.

Imaging: They typically appear as large, relatively well-defined masses with minimal or no peritumoral edema [Figure 5]. On NCCT, they appear as iso-hyperdense masses with areas of cyst formation and calcification within. On MRI, they show variable signal intensity depending on the presence of hemorrhage, necrosis, or calcification. They restrict on DWI due to high cellularity and show strong heterogenous contrast enhancement in the solid components. These tumors also tend to show cerebrospinal fluid density (CSF) dissemination.{Figure 5}

Low-grade gliomas

Gliomas account for nearly 50% of pediatric brain tumors. Low-grade gliomas (LGGs) are WHO grades I and II tumors.[6] They are usually located in the cerebellum, although tumors in the midline diencephalon are also quite common.

Pilocytic astrocytomas

This is the most common pediatric brain tumor and accounts for nearly 15% of all brain tumors in children.[6] These are benign WHO grade I tumors commonly occurring in the cerebellum. They can occur sporadically or can have a syndromic association, most common being NF-1. Sporadic tumors are commonly associated with B-Raf proto-oncogene serine/threonine-protein kinase (BRAF fusion).[6] In patients with NF-1, tumors frequently occur around the optic pathway and hypothalamus. Peak incidence is in the age group of 5 to 15 years.

Imaging: Hemispheric tumors are classically described as nonenhancing cystic lesions with enhancing mural nodules on both CT and MRI [Figure 6]. However, they can appear as solid enhancing lesions especially when seen around the hypothalamus and optic chiasma and can show central nonenhancing necrotic components.{Figure 6}

On MRI, the solid component appears hypointense on T1WI and hyperintense on T2WI with intense postcontrast enhancement. The cystic component shows a subtle hyperintense signal compared to the CSF on both T1WI and T2WI with incomplete suppression on FLAIR and no restriction on DWI. Contrary to other benign neoplasms, they exhibit elevated choline and low NAA peak on MRS. The regional cerebral blood volume has been found to be close to or mildly higher than normal brain parenchyma.[3]

Dysembryoplastic neuroepithelial tumors

These are WHO grade I glioneuronal tumors and are one of the common causes of tumor-associated intractable epilepsy. DNETs are frequently associated with FGFR1 mutation.[6] An association with cortical dysplasia has been described. Temporal lobe is the most common location followed by frontal lobe. Patients usually present before 20 years of age.

Imaging: These are well-defined cortical/subcortical tumors that characteristically show a “bubbly” appearance on imaging [Figure 7]. They appear hypodense on NCCT with calcification seen in 20% of tumors. On MRI, they appear as well-demarcated multilobulated masses, hypointense on T1WI, and hyperintense on T2WI. Blooming foci may be seen on T2-star sequences. On FLAIR, a characteristic hyperintense rim can be seen. No significant mass effect or postcontrast enhancement is seen.{Figure 7}

Gangliogliomas

These are well-differentiated WHO grade I tumors containing both neuronal and glial elements. The commonly occurring genetic alteration is the BRAF V600E point mutation.[6] These are the most common cause of tumor-associated temporal lobe epilepsy. The peak incidence is between 15 and 20 years. Temporal lobe is commonly involved followed by the frontal and parietal lobes.

Imaging: GGs are cortically based tumors which can be completely solid or partially cystic with an enhancing mural nodule [Figure 8]. They can have a variable attenuation on NCCT and about 40% cases show calcification within. No significant mass effect or peritumoral edema is seen. Approximately, half of the tumors show postcontrast enhancement. On MRI, these tumors appear hypo-isointense on T1WI and hyperintense on T2WI with variable contrast enhancement.{Figure 8}

High-grade gliomas

These include WHO grade III anaplastic astrocytoma and WHO grade IV diffuse midline gliomas. Most of the infiltrating gliomas involve the brainstem. A subtype known as infantile high-grade glioma (HGG) has lesser mutational burden and is seen in children under 3 years of age with a better prognosis compared to other HGGs.[6] Most of the adult infiltrating gliomas are supratentorial, whereas the brainstem is the most common location in the pediatric population. Moreover, the genetic alterations such as IDH mutation and 1p/19q codeletion which are frequently seen in adult infiltrating gliomas are rarely seen in children.[5]

Although a significant overlap exists in the imaging features of both LGGs and HGGs, the presence of irregular ill-defined margins, significant peritumoral edema, and restricted diffusion point towards the diagnosis of HGGs.[6]

Diffuse midline glioma, histone H3 K27M mutant

Infiltrating gliomas of the brainstem in children were traditionally referred to as diffuse intrinsic pontine glioma (DIPG). Majority of the brainstem gliomas have the K27M mutation and are high grade tumors. As these tumors can also involve other midline structures such as thalami, cerebellum, and spinal cord, they have been placed under the recently defined category of diffuse midline gliomas, H3 K27M mutant.[6]

Imaging: DIPGs are diffusely infiltrating lesions of the brainstem with epicenter in the pons and cause expansion of the same. They appear hypointense on T1W1 and hyperintense on T2/FLAIR with indistinct margins. They can have an exophytic component which encroaches upon the basilar artery. They show minimal or no postcontrast enhancement [Figure 9]. Occasionally, areas of necrosis or hemorrhage may be present. Due to the aggressive nature of the tumor, contiguous involvement of the thalami and upper cervical spinal cord is often seen. Distant discontiguous supratentorial spread and leptomeningeal spread of disease are not infrequent.{Figure 9}

Ependymal tumors

These are a heterogenous group of tumors with distinct genetic alterations depending on the tumor location in the CNS. The tumor most commonly found in the pediatric population is ependymoma.

Ependymomas

Ependymomas are common tumors accounting for 10% of pediatric brain tumors. Most occur in the posterior fossa in children between 1 and 5 years of age. The classical ependymomas are WHO grade II tumors, whereas RELA fusion-positive ependymomas are assigned grade II or III depending on the amount of anaplasia.[5]

The infratentorial ependymomas are further classified into two subgroups based on the DNA methylation profiling as PF-EPN-A and PF-EPN-B. Although both these subtypes appear similar pathologically and radiologically, the PF-EPN-B subtype is more commonly seen in older children and young adults and tends to have a better prognosis compared to PF-EPN-A ependymomas and RELA fusion-positive ependymomas which occur in infants and young children with a less favorable prognosis. The supratentorial ependymomas are generally RELA fusion-positive ependymomas but less frequently have yes-associated protein 1 mutation. The former occurs in older children with a poor prognosis, whereas the latter occurs in infants and has a good prognosis. Spinal ependymomas are very rare in children and can be either classic or myxopapillary subtype. Deletion of chromosome 22q is encountered in the classic ependymoma, whereas myxopapillary ependymomas are characterized by a Warburg phenotype.[6]

Imaging: Almost 70% of ependymomas are infratentorial arising from the floor of the fourth ventricle.[7] They are relatively well-defined and plastic in nature. Tumors in the fourth ventricle can extend through the outflow foramina [Figure 10]. Supratentorial tumors are seen within the lateral ventricles or brain parenchyma and tend to be more bulky, aggressive looking with diffusion and perfusion characteristics compatible with high-grade tumors.{Figure 10}

On NCCT, these appear as mixed density lesions with the soft-tissue component appearing iso-hyperdense and intratumoral cysts appearing hypodense. Calcification is seen in approximately 50% of patients. Hemorrhage is also not uncommon. On MRI, the tumors appear heterogeneously hypointense on T1WI and hyperintense on T2WI with blooming foci seen on T2-star sequences. Usually, they do not show restricted diffusion on DWI. On postcontrast studies, solid components show heterogenous enhancement. On MRS, high myo-inositol levels can be seen. Ependymomas can also have CSF dissemination warranting imaging of the entire neuraxis.

Choroid plexus tumors

These tumors arise from the epithelium of the choroid plexus and three histological subtypes of the neoplasm are described, namely, choroid plexus papilloma (CPP; WHO grade I), atypical choroid plexus papilloma (aCPP; WHO grade II), and choroid plexus carcinoma (CPCa; WHO grade III). Based on molecular studies, three subgroups have been established: clusters 1 and 3 seen in children and cluster 2 seen in the adults. Cluster 3 tumors are aggressive and include most aCPP and all CPCa.[8]

Choroid plexus tumors (CPTs) are uncommon accounting for 2% to 4% of pediatric brain tumors.[9] CPPs are the fifth most common congenital brain tumors. CPPs are frequently seen in infants with the trigone of the lateral ventricle being the most common site. In adults, they are frequently infratentorial seen in the fourth ventricle and cerebellopontine angle. Imaging cannot distinguish CPPs from aCPPs. CPCas are rare tumors seen almost exclusively in the lateral ventricles in children less than 3 years of age. They are frequently associated with TP53 mutation when seen in patients with Li–Fraumeni syndrome. Hemorrhage and areas of necrosis are frequently seen with evidence of invasion of the adjacent brain parenchyma and distal metastasis.[10]

Imaging: CPPs are characteristically iso-hyperdense on NCCT and appear as lobulated masses with frond-like projections in the ventricles [Figure 11]. Hydrocephalus is very common partly due to abnormal secretion of CSF by the tumor. CPCas are more heterogenous with significant peritumoral edema and signs of parenchymal invasion [Figure 12]. On MRI, CPTs appear iso-hypointense on T1WI and hyperintense on T2WI with prominent flow voids. Blooming foci seen on T2-star sequences. correspond to areas of hemorrhage and calcification. Intense postcontrast enhancement is seen which is heterogenous in case of CPCas. CPCa also shows higher cerebral blood flow on perfusion imaging compared to CPP. CSF dissemination can be seen in CPPs, aCPPs, as well as CPCas.{Figure 11}{Figure 12}

Pineal parenchymal tumors

These are primary tumors of the pineal gland arising from the pinealocytes or from their precursors.

Pineoblastomas

These are uncommon WHO grade IV tumors of children comprising undifferentiated pineal cells with dismal prognosis. They can occur in association with familial retinoblastoma in which scenario they are referred to as trilateral retinoblastomas.[11]

Imaging: Pineoblastomas appear as large, bulky irregular masses, often with surrounding parenchyma invasion and hydrocephalus [Figure 13]. They appear hyperdense on NCCT. When calcifications are present, they occur at the periphery of the lesion as the tumor originates from the pineal gland. On MRI, they appear iso-hypointense on T1WI and iso-hyperintense on T2WI. The presence of hemorrhage and necrosis is responsible for tumor heterogeneity. They show restricted diffusion on DWI with strong heterogenous postcontrast enhancement. CSF dissemination is quite frequently seen.{Figure 13}

Germ cell tumors

Germ cell tumors (GCTs) are the most common neoplasms involving the pineal gland and account for approximately 3% to 8% of pediatric brain tumors.

Germinomas

Germinomas are the most common intracranial GCTs accounting for 50% to 60% of intracranial GCTs.[6] Majority are located in the pineal region followed by suprasellar region. Most people are younger than 20 years.[12] The earliest clinical presentation is diabetes insipidus in most cases of suprasellar germinomas.

Imaging: Germinomas appear as well-defined relatively homogenous lesions that are hyperdense on NCCT. Pineal gland calcifications are typically engulfed by the tumor. On contrast-enhanced computed tomography (CECT), avid homogenous enhancement is seen. On MRI, they appear hypointense on TIWI and hyperintense on T2WI with restricted diffusion on DWI due to high cellularity. Foci of blooming on GRE/SWI sequences represent areas of calcification. Strong nearly homogenous enhancement is seen on postgadolinium MRI. They have a tendency for CSF dissemination.

Teratomas

Teratomas comprise only 0.3% to 0.6% of all intracranial neoplasms.[13] These are the most common congenital brain tumors.[7] Three subtypes have been recognized, namely, mature, immature teratomas, and teratomas with malignant transformation. Mature teratomas consist of well-differentiated tissue elements derived from more than one germ cell layer.

Imaging: The appearance on imaging depends upon the types of tissues and their relative proportions [Figure 14]. On CT, they are heterogenous due to the presence of bone, fat, calcification, cystic components, etc. Similarly, the MR signal characteristics depend on the tumor composition. Teratomas can rupture resulting in chemical meningitis. Malignant transformation is indicated by invasion of adjacent brain parenchyma. Obstructive hydrocephalus can also occur. MRS shows an elevated lipid peak.{Figure 14}

Tumors of the sellar region

These include craniopharyngiomas (CPs), pituicytomas, and so on.

Craniopharyngiomas

These are benign, WHO grade I neoplasms accounting for approximately 5% to 10% of childhood brain tumors.[1] Tumors are primarily suprasellar in location with two subtypes, namely, adamantinomatous CP and papillary CP. Mutation involving the WNT signaling pathway has been detected in the more common adamantinomatous subtype.[14] This subtype is mostly seen in children between 5 and 15 years of age.

Imaging: The adamantinomatous subtype frequently shows a mixed solid-cystic appearance with areas of calcification within [Figure 15]. The rule of 90 applies to this subtype, wherein 90% tumors are solid-cystic, 90% calcify, and 90% show enhancement on postcontrast imaging. On CT, the cystic components appear hypodense, whereas foci of calcification appear hyperdense. On MRI, cyst fluid can have variable signal intensity depending on the presence of hemorrhage, proteinaceous contents, or cholesterol granules. Classically, the cyst appears hyperintense on T1WI giving “motor oil” appearance. The solid component is usually calcified and appears hypointense on T2WI. Postgadolinium scans show enhancement of solid components and cyst walls. This subtype tends to be locally invasive. On the other hand, papillary tumors tend to be solid, encapsulated frequently located in the third ventricle with calcification being very rare.{Figure 15}

Hypothalamic hamartoma

Although considered to be non-neoplastic congenital anomalies of neuronal migration, these have been discussed under the sellar tumors due to their location. Most are located in the tuber cinereum which is the region between the infundibular stalk anteriorly and the mammillary bodies posteriorly. They can be associated with Pallister–Hall syndrome. Patients present with precocious puberty and occasionally gelastic seizures. The lesions can either be sessile or pedunculated.[15]

Imaging: They are homogenous lesions appearing isodense to brain on NCCT with no enhancement on CECT. On MRI [Figure 16], they appear isointense to the normal gray matter on T1WI/T2WI although they may appear mildly hyperintense on T2WI. No enhancement is seen following gadolinium administration. MRS shows elevated myoinositol peak.[15]{Figure 16}

Lymphomas

They can be primary or secondary to systemic involvement. They are usually seen in the elderly population and rarely seen in children. Non-Hodgkin’s B-cell lymphomas are the most common primary CNS lymphomas.[16] Lymphomas in the CNS can show focal or diffuse involvement of the dura, leptomeninges, or calvarial bone marrow. Parenchymal involvement is common in primary CNS lymphomas, whereas secondary lymphomas tend to involve the leptomeninges and have a poor prognosis.[16] Spinal involvement is not uncommon with lymphomatous infiltrates seen in the bone marrow or meninges.[17]

Imaging: Due to the high cellularity of the lesion lymphomas appear hyperdense on NCCT compared to the brain. Marked perilesional edema is frequently seen. They show relatively homogenous postcontrast enhancement. Abnormal leptomeningeal enhancement can be seen in case of involvement. On MRI, they appear hypointense on T1WI and T2WI showing homogenous enhancement on T1+C images [Figure 17]. Calcification, necrosis, and hemorrhage are very rare unless the patient is immunocompromised. Bone marrow involvement appears as low signal intensity on T1WI.{Figure 17}

Miscellaneous

Tumors associated with neurocutaneous syndrome

Neurofibromatosis: NF-1 and NF-2 are genetically distinct inherited autosomal dominant disorders. NF-1 is the most common phacomatoses having numerous systemic manifestations.[18] The CNS tumors commonly associated include optic nerve glioma and astrocytoma. NF-2 predisposes to the development of acoustic schwannomas, meningiomas, ependymomas, and gliomas. The term “MISME” has been used for the spectrum of imaging findings in NF-2 which include multiple inherited schwannomas (MIS), meningiomas (M), and ependymomas (E) [Figure 18]. Spinal involvement by tumors is not uncommon and aids in the diagnosis of NF-2.[19]{Figure 18}Tuberous sclerosis (TS): It is a rare congenital phacomatosis involving primarily the skin and CNS. It is characterized by the presence of epilepsy, mental retardation, and adenoma sebaceum.[20] CNS involvement is seen in the form of cortical tubers, subependymal nodules and white matter abnormalities, and subependymal giant-cell astrocytomas (SGCAs).SGCAs : These are benign WHO grade I tumors seen in 1.7% to 26% patients with TS occurring frequently in patients between 8 and 18 years of age.[20] They are slow growing tumors typically located at the foramen of Monro.Imaging: On NCCT, they appear as well-defined iso-hypoattenuating masses which may show foci of calcification within. They are usually larger than 1 cm and show more avid enhancement compared to subependymal nodules. Hence, whenever a subependymal incompletely calcified nodule more than 5 mm in size is encountered at the foramen of Monro, follow-up imaging is advised. On MRI, they show heterogenous signal on T1WI/T2WI with uniform postcontrast enhancement [Figure 19]. MRS may help in distinguishing SEGA from nodules as SGCAs show high Cho/Cr and low NAA/Cr ratios.[21]{Figure 19}Von Hippel–Lindau disease (VHL): The VHL is an autosomal dominant disorder causing ocular and CNS hemangioblastomas along with various other neoplasms throughout the body. Hemangioblastomas are seen commonly in the cerebellum, spine, and medulla. About 5% to 30% of cerebellar hemangioblastomas are associated with VHL and occur in younger patients with worse prognosis.[22] On imaging, they appear as well-defined lesions which are entirely solid or cystic with a mural nodule that enhances on postcontrast studies.

Metastases

Brain metastases are uncommon in the pediatric population. The tumors commonly causing metastases include Ewing sarcoma, neuroblastoma, Wilms tumor, soft-tissue sarcoma, osteogenic sarcoma, and GCTs.[23] The imaging characteristics are variable with most hematogenous tumors being located in the cortical/subcortical location appearing isointense to gray matter on T1WI and mildly hyperintense on T2WI. Peritumoral edema, hemorrhage, and calcification can occur depending on the primary. They can restrict on DWI. Enhancement is variable.

Tumor-like lesions

Epidermoid cysts: These are the most common embryonal intracranial lesions thought to arise from displaced ectodermal cell rests resulting from aberrant neural tube closure. These are commonly located in the cerebellopontine angle. On CT, they appear as well-demarcated low-density lesions with scalloped/irregular margins. The adjacent bone may show resorption. Occasionally, calcification may be seen within. No obvious postcontrast enhancement is seen. On MRI, they appear heterogenous with low signal intensity on T1WI and high signal on T2WI with no gadolinium enhancement. They characteristically show incomplete suppression on FLAIR and restricted diffusion on DWI [Figure 20]. They surround adjacent vessels, whereas arachnoid cysts displace them.[24]{Figure 20}Arachnoid cysts: These are congenital intra-arachnoid CSF collections forming intracranial mass-like lesions comprising ∼1% of all intracranial lesions.[24] The middle cranial fossa is the most common location followed by cerebellopontine angle. On CT, they appear as sharply defined cystic extra-axial lesions of CSF density with rounded margins exerting mass effect on adjacent brain parenchyma. On MRI, they follow CSF signal intensity on all sequences. They do not show restricted diffusion on DWI and do not enhance on postgadolinium images.[24]

 Conclusion



Brain tumors are the most common solid pediatric neoplasms. They differ from adult neoplasms and have distinct genetic and imaging characteristics. The diagnosis depends on the age of the patient, tumor location, and imaging characteristics. Medulloblastomas show the highest correlation between imaging and tumor genetics. Patients with the low-risk WNT subtype benefit from surgery and chemotherapy, whereas the groups 3 and 4 medulloblastomas require a more aggressive multimodality approach along with more frequent tumor monitoring and can benefit from targeted therapies.[25] As the genetic and molecular subtype of the tumors influence patient management and prognosis, it is essential for the radiologists to be familiar with the imaging features of genetic tumor subtypes.

Acknowledgment

The authors acknowledge Dr Vijaylaxmi for her valuable inputs toward the making of this article.

Authors’ contributions

All authors have contributed in the design and conceptualization of the article, literature search, manuscript preparation, review, and editing.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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