Conventional and Advanced MRI Features of Pediatric Intracranial Tumors: Posterior Fossa and Suprasellar Tumors

Transcription

1 Neuroradiology/Head and Neck Imaging Review Plaza et al. MRI of Posterior Fossa and Suprasellar Tumors Neuroradiology/Head and Neck Imaging Review Michael J. Plaza 1 Maria J. Borja 1 Nolan Altman 2 Gaurav Saigal 1 Plaza MJ, Borja MJ, Altman N, Saigal G Keywords: advanced neuroimaging, diffusion-weighted imaging, MR spectroscopy, pediatric brain tumors, perfusion MRI, posterior fossa, tractography DOI: /AJR Received August 5, 2012; accepted after revision November 18, Department of Radiology, University of Miami/Jackson Memorial Hospital, 1611 NW 12th Ave, West Wing 279, Miami, FL Address correspondence to M. J. Borja (MBorja2@med.miami.edu). 2 Department of Radiology, Miami Children s Hospital, Miami, FL. CME/SAM This article is available for CME/SAM credit. AJR 2013; 200: X/13/ American Roentgen Ray Society Conventional and Advanced MRI Features of Pediatric Intracranial Tumors: Posterior Fossa and Suprasellar Tumors OBJECTIVE. In this article, we review the most common posterior fossa and suprasellar intracranial neoplasms in the pediatric population. We briefly discuss basic MRI concepts used in the initial evaluation of a pediatric brain tumor and then discuss sophisticated MRI techniques that give insight into the physiology and chemical makeup of these tumors to help the radiologist make a more specific diagnosis. CONCLUSION. Diagnosis and treatment of pediatric CNS tumors necessitate a multidisciplinary approach and require expertise and diligence of all parties involved. Imaging is an essential component has evolved greatly over the past decade. We are becoming better at making a preoperative diagnosis of that tumor type, detecting recurrence, and guiding surgical management to avoid injury to vital brain structures. I nfratentorial tumors account for 45 60% of all pediatric brain tumors, and the most common infratentorial tumors include juvenile pilocytic astrocytoma (JPA), medulloblastoma, ependymoma, and brainstem glioma [1]. Less commonly we encounter atypical teratoid-rhabdoid tumor (ATRT) and hemangioblastoma, but they are important to recognize and discuss because they mimic the more common tumors radiologically. An accurate diagnosis has important clinical implications related to prognosis and treatment. Pediatric suprasellar tumors are unique in their differential diagnosis and differ from adult tumors in the same region in incidence and treatment. We focus on craniopharyngiomas because they are one of the most common tumors arising from the pituitary region in children and on suprasellar gliomas and hypothalamic hamartomas because of their unique clinical presentations and imaging features. The differential diagnosis of pediatric brain tumors begins with an accurate assessment of lesion location, which is often the most important diagnostic feature provided by conventional MRI. Advanced MR neuroimaging techniques allow assessment of the physiologic features of brain tumors, resulting in better preoperative characterization and often in better outcomes. Posterior Fossa Tumors Pilocytic Astrocytoma Cerebellar astrocytomas account for 30% of all posterior fossa tumors in children, with the most common histologic subtype being JPA [2]. The majority of JPAs, 60%, arise from the cerebellum. Five percent of patients with neurofibromatosis type 1 (NF1) will develop a cerebellar JPA, although the most common location for pilocytic astrocytoma in NF1 patients is the optic nerve or optic chiasm [3]. Clinical presentation varies with the site of origin, but most patients present with headache, neck pain, gait disturbance, and vomiting. The classic imaging appearance of a JPA, which is observed in 30 60% of cases, is of a large cyst with a solid mural nodule within one of the cerebellar hemispheres; less commonly, JPA may present on imaging as a predominantly solid mass with little to no cystlike component [4]. On MRI, the cystic portion is hypointense relative to gray matter on T1-weighted images and hyperintense relative to gray matter on T2-weighted images. JPA is a low-grade neoplasm (World Health Organization [WHO] grade I [5]) that results in diminished surrounding vasogenic edema in comparison with highgrade tumors. Enhancement patterns may vary, but JPA most commonly (46%) appears as a cyst with an enhancing wall and an intensely enhancing mural nodule [6] (Fig. 1). AJR:200, May

2 Plaza et al. Fig. 1 2-year-old boy who presented with severe headaches due to cerebellar pilocytic astrocytoma. A and B, Axial unenhanced CT (A) and T2-weighted MR (B) images show predominantly right cystic hemispheric mass with nodular mural wall. C and D, Unenhanced (C) and contrast-enhanced (D) sagittal T1-weighted MR images show enhancing cyst wall and enhancing mural nodular components. E, MR spectroscopy image (TE = 80 ms) with region of interest over solid component of mass shows paradoxical aggressive metabolite pattern (increased choline [Cho] and reduced N-acetyl aspartate [NAA] levels) despite classification as low-grade tumor with nonaggressive clinical behavior. Glx = glutamine and glutamate, mi = myoinositol, Cr = creatine. Diffusion-weighted imaging (DWI) of JPAs shows no restricted diffusion, which is consistent with the characteristics of a low-grade tumor. MR spectroscopy (MRS) performed on the solid portion of pilocytic astrocytomas shows elevated choline-to N-acetyl aspartate (NAA) ratios and elevated lactate levels, which is an aggressive metabolite pattern. This pattern is paradoxical because it does not reflect the quiescent clinical behavior of the tumor [7]. The elevated lactate levels in JPAs do not reflect necrosis, which is rare in pilocytic astrocytomas and, rather, reflect aberrant glucose utilization [7]. Although there are no diffusion-tensor imaging (DTI) data in reference to cerebellar JPAs to date, DTI has been shown to be a useful adjunct in differentiating thalamopeduncular pilocytic astrocytomas from infiltrating tumors in the posterior fossa because pilocytic astrocytomas displace corticospinal tracts, whereas other tumors may encase them or disrupt them [8]. JPAs may mimic hemangioblastomas on conventional MRI by appearing as a cystic mass with an enhancing mural nodule; however, perfusion MRI may confidently allow distinction between these tumors because relative cerebral blood volume (rcbv) has been shown to be significantly less in JPAs than in hemangioblastomas [9] (Fig. 2). The treatment goal in patients with JPA is gross total resection; this goal is achieved in 60 80% of operative cases with a 10-year survival rate of more than 94% [6, 10]. Medulloblastoma Medulloblastoma accounts for 35 40% of all posterior fossa tumors in children with peak occurrence at approximately 4 years old [2, 11]. Patients typically present with hydrocephalus, headache, and ataxia. Classic medulloblastoma typically arises from the roof of the fourth ventricle and is midline in location in 75 90% of cases. Desmoplastic medulloblastoma is a rare histologic variant that typically occurs off midline in the cerebellar hemisphere [1, 12]. Classic medulloblastoma is a highly cellular, densely packed tumor, which is reflected on imaging; it appears hyperdense relative to brain on CT (89% of cases) and shows restricted diffusion on DWI [13] (Fig. 3). Investigations of the utility of DWI for differentiating among posterior fossa tumors have shown that apparent diffusion coefficient (ADC) values are significantly lower in medulloblastoma. This feature of medulloblastoma allows differentiation from JPA, ependymoma, and brainstem glioma [1]. In fact, in one study, cutoff ADC values of less than mm 2 /s for medulloblastoma and of more than mm 2 /s for JPA were found to be 100% specific [14]. On the other hand, the ADC values of medulloblastoma and ATRT overlap [1]. Medulloblastoma is a high-grade tumor, so it can be differentiated from low-grade posterior fossa tumors on the basis of its increased rcbv on perfusion MRI [15]. T2-weighted imaging shows heterogeneous signal: The solid components appear hypointense relative to gray matter because of the highly cellular nature of the tumor and the cystic components, which are seen in 59% of cases, appear hyperintense [13]. Calcifications can be found in up to 20% of cases and hemorrhage is rare [1]. Approximately 92% of medulloblastomas enhance; however, enhancement may be variable in degree, ranging from diffuse homogeneous enhancement to very little patchy enhancement [16, 17]. Medulloblastomas generally have the characteristic spectrographic signature for a neuroectodermal tumor with high taurine, depleted NAA, and prominent choline and lipid peaks [18]. Because treatment of patients with medulloblastoma involves craniospinal radiation, DTI and DWI are potentially useful in early detection and monitoring of radiation-induced white matter injury through the measure of fractional anisotropy (FA) and ADC values [19, 20]. At diagnosis, 14 43% of patients with medulloblastoma are reported to have microscopic or nodular seeding of the subarachnoid space; therefore, at the time of diagnosis, an MRI examination of the entire spine should be performed to determine if there is leptomeningeal dissemination [21]. Treatment includes surgical excision with adjuvant chemotherapy and craniospinal irradiation if the child is older than 3 years old. Patients with average-risk disease that is, those with no metastases or gross residual tumor after resection have a 5-year survival of 80% [22]. The 5-year sur AJR:200, May 2013

3 MRI of Posterior Fossa and Suprasellar Tumors vival was shown to be 100% in one series of 26 patients with average-risk disease and tumor markers negative for ERBB2 [23]. This survival rate is in comparison with the 20% 5-year survival in patients with high-risk disease according to their clinical profile. Atypical Teratoid-Rhabdoid Tumor ATRT constitutes 1 2% of pediatric brain tumors and has a predilection for infants; it most commonly occurs in children younger than 3 years old [24]. Within the CNS, ATRT most commonly occurs infratentorial and off midline, 38 65%; however, in 4 8% of the cases, tumors are present at multiple CNS sites at the time of diagnosis [25]. ATRT mimics medulloblastoma radiologically and histologically and has been misdiagnosed in the past. ATRTs can now be differentiated from medulloblastomas using specific immunohistochemical markers and by detecting certain gene mutations or deletions, such as the lack of INI1 expression on immunohistochemical stains [26]. Conventional MRI shows heterogeneous signal intensity on T1- and T2-weighted pulse sequences because the mass commonly contains cysts, hemorrhage, and calcifications [26]. Eccentrically located cysts may favor the diagnosis of ATRT over primitive neuroectodermal tumor and medulloblastoma [26]. A highly aggressive appearance of a tumor with skull invasion may favor ATRT over other cystic masses such as JPA or desmoplastic infantile ganglioglioma. The enhancement pattern of ATRTs is most commonly heterogeneous and is rarely homogeneous, reflecting the complex histopathology of this tumor [25]. Restricted diffusion is typi- Fig. 2 5-year-old girl with pathologically proven pilocytic astrocytoma. A and B, Axial unenhanced (A) and coronal contrastenhanced (B) T1-weighted MR images show right cerebellar cystic mass with enhancing solid mural component medially. C and D, Perfusion MRI. Source image (C) and color map of cerebral blood volume (D) show minimal angiogenesis within medial solid component of mass. L3 and L1 = regions of interest. cal. MRS shows an aggressive metabolite pattern with elevated choline, decreased or absent NAA, and prominent lipid and lactate peaks (Fig. 4). Treatment of ATRT involves surgery and chemotherapy. Radiation is rarely an option because of the young age of the patient; however, some evidence suggests that early radiotherapy in patients younger than 3 years may be beneficial [27]. Distinguishing between an ATRT and a medulloblastoma is important because the prognosis associated with ATRT is worse than that associated with medulloblastoma. The mean survival time of patients with ATRT is 11 months, necessitating highly aggressive chemotherapy regimens different from those used to treat patients with medulloblastoma [25, 26]. The ADC values of the two tumors are similar: ATRT, 0.55 ± mm 2 /s (mean ± SD); and medulloblastoma, 0.47 ± mm 2 /s [28]. A younger patient age, intratumoral hemorrhage, and cerebellopontine angle involvement favor a preoperative diagnosis of ATRT over medulloblastoma [28]. Ependymoma Ependymoma is the third most common posterior fossa tumor in children. Incidence peaks in patients 0 4 years old. Approximately 70% of intracranial ependymomas are infratentorial and arise from ependymal cells lining the floor of the fourth ventricle and foramen of Luschka [29]. Patients most commonly present with headache, nausea, and vomiting and have a prolonged time to presentation, reflecting the slow growth of the tumor. Neurofibromatosis type 2 (NF2) is the only known genetic disorder associated with a predisposition for ependymomas; however, NF2 patients typically develop the intramedullary spinal type of ependymoma [29]. Histologically, ependymomas tend to have a high proportion of intracellular myxoid accumulation and cyst formation. These features are reflected on conventional MRI as high signal intensity relative to uninvolved gray matter on T2-weighted and FLAIR pulse sequences [29]. Areas of low signal intensity relative AJR:200, May

4 Plaza et al. to gray matter on T2-weighted images and FLAIR images may represent calcifications or hemorrhage. Sagittal images may be the key to the diagnosis in some cases because sagittal images can be used to identify the point of origin as the floor of the fourth ventricle, as seen in ependymoma, versus the roof, as seen in medulloblastoma. Calcification is a common feature seen in 50% of ependymoma cases and contrast enhancement is heterogeneous. Although not pathognomonic, the plastic nature of ependymoma results in the classic presentation of a fourth ventricle mass extending through the foramen of Luschka (15%) or foramen of Magendie (60%) [29] (Fig. 5). Some ependymomas may show restricted diffusion, but diffusivity values are not completely reliable in making a histologic diagnosis. Perfusion MRI patterns for ependymomas are variable and are likely related Fig. 3 5-year-old boy with pathologically proven medulloblastoma. A, Axial unenhanced CT image shows hyperdense mass in fourth ventricle. Dilatation of temporal horns is noted. This finding is consistent with hydrocephalus. B, Axial T2-weighted image shows mass to be predominantly isointense relative to normal gray matter. C and D, Axial diffusion-weighted image (C) and apparent diffusion coefficient map (D) show restricted diffusion within mass. to the histologic subtype [18, 29]. However, in general, perfusion MRI of ependymomas shows markedly elevated cerebral blood volume (CBV) and poor return to baseline CBV, which is attributable to the fenestrated blood vessels observed microscopically [29]. MRS generally shows depleted NAA and elevated choline and lactate levels, but the primary application of MRS in the setting of ependymoma is to evaluate for tumor recurrence versus posttreatment change [29]. The most important prognostic factor is the extent of surgical resection, so the goal of treatment is gross total resection [30]. However, complete resection of posterior fossa ependymomas is often difficult because of adherence and infiltration of vital structures. Thus, radiation is considered the standard adjuvant treatment of ependymomas in older children. Radiotherapy may also be combined with chemotherapy when postoperative residual disease is present. Brainstem Glioma Brainstem gliomas comprise approximately 10 20% of all intracranial tumors in children and 75% of brainstem gliomas occur in patients younger than 10 years [31, 32]. Brainstem gliomas are not designated as a specific pathologic category in the WHO classification of CNS tumors [5] and are classified by location rather than histology. They are classified broadly as diffuse intrinsic gliomas or as nondiffuse brainstem tumors. The diffuse intrinsic tumor type is the most common, with an approximate frequency of 75 85% [33]. The peak incidence of brainstem gliomas is in patients 3 10 years old. The classic triad of presentation long tract signs, cranial nerve deficits, and ataxia is seen simultaneously in 35% of patients, but most patients present with at least one of these symptoms [34]. Of interest are brainstem gliomas in NF1 patients because the tumors are more commonly in the medulla than the pons and because NF1 patients with brainstem gliomas have a more favorable prognosis than non-nf1 patients [1, 35]. On MRI, diffuse pontine gliomas characteristically expand the pons and are usually hypointense relative to gray matter on T1- weighted images and hyperintense relative to gray matter on T2-weighted and FLAIR images (Fig. 6). Most diffuse brainstem gliomas do not enhance; however if they do enhance, enhancement is very little and heterogeneous [1]. The focal midbrain tumor type has variable enhancement depending on which part of the midbrain is involved, the cervicomedullary tumor type commonly enhances, and the dorsal exophytic tumor type commonly enhances homogeneously [33]. The utility of assessing enhancement of brainstem gliomas is in the follow-up of patients to identify response to therapy or recurrence [36]. Currently, the data in the literature about whether tumor enhancement at baseline and over 1118 AJR:200, May 2013

5 MRI of Posterior Fossa and Suprasellar Tumors Fig. 4 4-month-old female infant with pathologically proven atypical teratoid-rhabdoid tumor. A, Axial T1-weighted image shows heterogeneous posterior fossa mass and punctate areas that are hyperintense (arrow) relative to gray matter; these areas represent subacute hemorrhage. B, Axial T2-weighted image shows heterogeneous signal within mass with eccentric high-signal-intensity cysts (arrow). C and D, Axial diffusion-weighted image (C) and apparent diffusion coefficient map (D) show restricted diffusion in mass. E, MR spectroscopy image (TE = 80 ms) shows choline (Cho) peak is markedly elevated, which is consistent with highly aggressive metabolite pattern. Markedly elevated lipid (lip) peak is also noted. Cr = creatine, NAA = N-acetyl aspartate. Fig. 5 6-year-old girl with pathologically proven ependymoma. A, Axial T1-weighted image shows mass is hypointense relative to gray matter and that it arises from fourth ventricle and extends through right foramen of Luschka into cerebellopontine angle (arrow). B, Axial contrast-enhanced T1-weighted image shows heterogeneous enhancement of mass (arrow). C, Sagittal contrast-enhanced T1-weighted image shows heterogeneously enhancing mass arises from floor of fourth ventricle with relative uninvolvement of roof (arrow). AJR:200, May

6 Plaza et al. Fig. 6 7-year-old girl who presented with left facial palsy secondary to diffuse intrinsic brainstem glioma. A C, Axial unenhanced (A), axial contrast-enhanced (B), and coronal contrast-enhanced (C) T1-weighted images show diffuse infiltrative mass centered in pons. Mass is hypointense relative to gray matter on T1-weighted pulse sequences with peripheral enhancement. Mass effect and displacement of fourth ventricle are visible. D, Axial FLAIR MR image shows indiscrete areas of hyperintensity relative to gray matter. E, Diffusion-tensor image in coronal plane shows left-sided corticospinal tracts (arrow) are deviated toward right secondary to brainstem glioma. time provides prognostic information related to survival are conflicting [37]. Most diffuse gliomas do not show restricted diffusion and ADC values are characteristically higher than in medulloblastomas [1]. Most diffuse brainstem gliomas are histologically low grade, but a subset rapidly evolves into highgrade neoplasms; on advanced imaging techniques, high-grade neoplasms are suggested by focal areas of restricted diffusion and increased rcbv. These findings likely correspond to areas of anaplasia [38]. DWI and perfusion MRI allow us to analyze the tumor field by region rather than globally so early identification of focal anaplasia in a brainstem glioma is possible. This information has implications in terms of prognosis, management, and biopsy guidance [38]. Moreover, MRS shows utility in establishing a brainstem glioma s baseline metabolic profile so subsequent metabolic changes on serial MRS can be used as markers for disease progression [18]. Malignant degeneration is suggested by increased lipids and reduced NAA-to-choline, creatine-to-choline, and myoinositol-to-choline ratios. Importantly, identifying increased choline concentrations on serial MRS may precede clinical worsening by up to 5 months [18]. Last, in a review of MR spectra acquired from various pediatric brain tumors, diffuse intrinsic brainstem gliomas had higher 1120 AJR:200, May 2013

7 MRI of Posterior Fossa and Suprasellar Tumors mean concentrations of citrate than ependymomas, medulloblastomas, and JPAs [39]. With respect to brainstem gliomas, DTI plays an essential role in diagnosis and surgical planning. Demyelinating diseases may mimic diffuse intrinsic brainstem gliomas clinically and on conventional imaging techniques; however, tractography clearly distinguishes between the two because brainstem gliomas deflect white matter tracts whereas demyelinating diseases result in truncated fibers [40] (Fig. 6). Tractography allows visualization of spatial relations between tumor and adjacent fiber tracts; in operable brainstem glioma tumor types, tractography provides important presurgical information because preservation of white matter tracts correlates with better neurologic and functional outcomes after surgery [1]. Diffuse intrinsic gliomas are nonoperative. The standard treatment is fractionated external beam radiotherapy, with chemotherapy reserved for cases of tumor progression despite radiotherapy. The diffuse intrinsic type has the worst prognosis of all brainstem gliomas, with median survival rarely exceeding 9 months [41]. Focal midbrain tumors have a more indolent course and a more favorable prognosis. In fact, some small tectal gliomas can be followed often with serial MRI and alleviation of hydrocephalus as needed with shunt placement or third ventriculostomy [42]. Tegmental and other nontectal midbrain tumors tend to be larger and benefit from resection or debulking [43]. Surgery is the mainstay of treatment of dorsally exophytic tumors and cervicomedullary tumors. Tractography reportedly has potential use in assessing response to treatment of brainstem gliomas and may be diagnostic of tumor progression [44]. Hemangioblastoma Hemangioblastomas account for 1 3% of all intracranial neoplasms, and most occur in middle-aged adults. In children younger than 18 years old, these tumors are extremely rare, with an incidence of less than 1 per 1 million [45]. One of the most common manifestations of von Hippel Lindau (VHL) syndrome is Fig year-old man with von Hippel Lindau syndrome. A C, Axial unenhanced (A), axial contrast-enhanced (B), and coronal contrast-enhanced (C) T1-weighted images show cystic mass in cerebellum with homogeneously enhancing mural nodule medially; these findings are consistent with hemangioblastoma. D, FLAIR image shows solid component of mass to be hyperintense to gray matter. E, Diffusion-weighted image. Solid component of mass shows no restricted diffusion. AJR:200, May

8 Plaza et al. multiple CNS hemangioblastomas, with the most common site of presentation being in the cerebellum (44 72%) [46]. Approximately 25 40% of hemangioblastomas are associated with VHL syndrome. Patients with cerebellar hemangioblastomas typically present with headache, vertigo, ataxia, and ninth cranial nerve palsy; in some cases, polycythemia has been noted given that up to 40% have been reported to secrete erythropoietin [47]. Hemangioblastomas are highly vascular tumors and may present as a mural nodule within a large cyst cavity (45%) or a purely solid tumor (45%) [47]. Typical hemangioblastomas are hypo- to isointense relative to gray matter on T1-weighted pulse sequences and hyperintense relative to gray matter on T2-weighted pulse sequences with enhancement of the mural nodule (Fig. 7). The cyst wall most commonly does not enhance unless lined by neoplasm [47]. Large feeding and draining vessels in the periphery and within the solid component appear as tubular flow voids on T2-weighted imaging. Hemangioblastomas mimic pilocytic astrocytomas and pleomorphic xanthoastrocytomas in their imaging appearance, but because of their intrinsic high vascularity, hemangioblastomas have the highest rcbv [48]; thus, perfusion MRI may be a useful diagnostic adjunct. En bloc surgical resection is considered the standard of care in adults with cerebellar hemangioblastomas. Data about the appropriate management of children and adolescents with VHL presenting with multiple hemangioblastomas are limited. Recurrence rates range from 8% to 25% and the recurrent tumor may not necessarily have the same morphology as the original tumor [47, 49]. Sellar and Suprasellar Tumors Craniopharyngioma Craniopharyngiomas are benign tumors that arise from squamous epithelium. They represent 50% of suprasellar tumors in children; most cases are diagnosed in children who are 4 5 years old, with a second incidence peak during the fourth to fifth decades [50, 51]. Craniopharyngiomas can arise in the sellar region, suprasellar region, or both. Because of the location of this tumor, patients commonly present clinically with visual disturbance, due to compression of the optic chiasm; endocrinologic disorders, from involvement of the hypothalamus and pituitary; or headache and hydrocephalus. Nearly 90% of craniopharyngiomas are suprasellar, are cystic with calcifications, and have nodular or rim enhancement on CT [50, 52]. CT is particularly helpful in the identification of these lesions because of its high sensitivity for calcification. On MRI, the cystic component may be hypo- or hyperintense relative to gray matter on T1-weighted pulse sequences (Fig. 8) because of the liquid cholesterol component, methemoglobin, or proteinaceous fluid [52]. The solid component may be iso- or hypointense on T1-weighted images and iso- or hyperintense relative to gray matter on T2-weighted images. Calcifications usually appear as low signal on T2-weighted imaging. The signal characteristics of craniopharyngiomas on DWI and FLAIR imaging may vary depending on the viscosity of the fluid. If there is a high degree of viscosity, the tumor may appear hyperintense on FLAIR imaging and isointense on DWI with a slightly lower ADC than CSF [52]. MRS may help differentiate craniopharyngiomas from other suprasellar masses by depicting prominent peaks of lipids and cholesterol [52]. The differential diagnosis includes hypothalamic glioma, Rathke cleft cyst, and germ cell tumors [18]. Optic DTI may help in the preoperative evaluation and treatment of craniopharyngiomas because DTI has been proven useful in differentiating the optic nerves from chiasmatic or suprasellar tumors. Normal white matter tracts are usually associated with high FA values, which will allow depiction of the tracts by fiber-tracking software. On the contrary, abnormal white matter tracts with low FA values may not be seen on tractography [53]. Surgery of craniopharyngiomas is often limited because of the size of the tumor and invasion of adjacent structures, with a reported recurrence rate of 86% in tumors larger than 5 cm [50]. Radiotherapy may be needed in cases of subtotal resection, although complications from intracranial radiation, such as radiation-induced vasculopathy, may occur. Rarely, vasculopathy can progress to the development of moyamoya disease from occlusion of the internal carotid arteries. This complication occurs predominantly in children with tumors located in the parasellar region and near the circle of Willis, such as craniopharyngiomas and optic gliomas [54]. Hypothalamic Hamartoma Hypothalamic hamartomas are not true neoplasms. They are considered developmental malformations from mature ganglionic tissue that involve the tuber cinereum. Clinically patients with hypothalamic hamartoma can present with gelastic seizures, precocious puberty, and developmental delay. On CT, hypothalamic hamartoma appears as a homogeneous isodense suprasellar mass. On Fig. 8 5-year-old boy with craniopharyngioma. A, Axial unenhanced CT image on bone windows shows calcification (arrow) in suprasellar region. B and C, Sagittal unenhanced (B) and contrast-enhanced (C) T1-weighted images show large cystic, peripherally enhancing suprasellar mass (arrow) AJR:200, May 2013

9 MRI of Posterior Fossa and Suprasellar Tumors Fig year-old boy who presented with gelastic seizures secondary to surgically proven hypothalamic hamartoma. A and B, Axial T2-weighted (A) and sagittal T1-weighted (B) images show round mass (arrow) with homogeneous isointense signal relative to gray matter at level of tuber cinereum without significant mass effect on surrounding structures. No contrast enhancement was noted within mass (not shown). MRI, hypothalamic hamartoma can be identified by the presence of a small, well-defined pedunculated or sessile mass [55]. It is isointense relative to gray matter on T1-weighted images and is iso- to slightly hyperintense relative to gray matter on T2-weighted imaging, FLAIR imaging, and DWI without enhancement or calcification [55] (Fig. 9). Cysts are rarely visualized. MRS has shown increased myoinositol levels with decreased or normal NAA levels [55, 56]. Data regarding the use of perfusion MRI and tractography of this malformation for the pediatric population are limited. The differential diagnosis includes germinoma and hypothalamic glioma [56]. Treatment of hypothalamic hamartomas involves medical management of the seizures and hormonal imbalance. Surgery is required if medical management fails. Hypothalamic and Chiasmatic Gliomas Hypothalamic and chiasmatic gliomas represent 10 15% of pediatric supratentorial tumors, 20 50% of which are associated with NF1 [50]. Histologically, they are mostly pilocytic astrocytomas and low-grade astrocytomas and the distinction between chiasmatic origin and hypothalamic origin may be difficult [50]. Clinical presentation includes visual abnormalities, hypothalamic dysfunction, hypopituitarism, precocious puberty, and hydrocephalus. Hypothalamic and chiasmatic gliomas appear hypointense relative to gray matter on T1-weighted pulse sequences and hyperintense relative to gray matter on FLAIR and T2-weighted pulse sequences with homogeneous enhancement. The MRS spectral pattern is similar to those of other astrocytomas with a dominant choline peak [15]. Elevated ADC values ( 1.41 μm 2 /ms) similar to those of pilocytic astrocytomas are also found [57]. Optic DTI is helpful for planning surgery of these tumors, as with craniopharyngiomas, by differentiating glioma from the optic nerve [53]. The differential diagnosis includes germ cell tumors, Langerhans cell histiocytosis, and inflammatory conditions. Hypothalamic and chiasmatic gliomas may be differentiated from germ cell tumors by the usual hyperintense signal on T2-weighted images compared with the hypointense signal of germ cell tumors [18]. The growth of these tumors is usually slow and may sometimes show spontaneous regression. Conclusion Diagnosis and treatment of pediatric CNS tumors necessitate a multidisciplinary approach and require the expertise and diligence of all parties involved. Imaging is an essential component in the care of these patients and has evolved greatly over the past decade. We are becoming better at making a preoperative diagnosis of the tumor type, detecting recurrence, and guiding surgical management to avoid injury to vital brain structures. Advanced neuroimaging, in combination with refined surgical techniques and progress in chemoradiation treatments, is resulting in better outcomes for affected children. References 1. Poretti A, Meoded A, Huisman TA. Neuroimaging of pediatric posterior fossa tumors including review of the literature. J Magn Reson Imaging 2012; 35: Drevelegas A. Imaging of brain tumors with histological correlations, 2nd ed. New York, NY: Springer-Verlag, Li J, Perry A, James CD, Gutmann DH. Cancer-related gene expression profiles in NF1-associated pilocytic astrocytomas. Neurology 2001; 56: Reddy ATM, Timothy B. Chapter 74: cerebellar astrocytoma. In: McLone DG, ed. Pediatric neurosurgery: surgery of the developing nervous system, 4th ed. New York, NY: Saunders, 2000: Louis DN, Ohgaki H, Wiestler OD, Cavenee WK, eds. WHO classification of tumours of the central nervous system, 4th ed. Lyon, France: The International Agency for Research on Cancer, Koeller KK, Rushing EJ. From the archives of the AFIP: pilocytic astrocytoma radiologic-pathologic correlation. RadioGraphics 2004; 24: Hwang JH, Egnaczyk GF, Ballard E, Dunn RS, Holland SK, Ball WS Jr. Proton MR spectroscopic characteristics of pilocytic astrocytomas. AJNR 1998; 19: Broadway SJ, Ogg RJ, Scoggins MA, Sanford R, Patay Z, Boop FA. Surgical management of tumors producing the thalamopeduncular syndrome of childhood. J Neurosurg Pediatr 2011; 7: Bing F, Kremer S, Lamalle L, et al. Value of perfusion MRI in the study of pilocytic astrocytoma and hemangioblastoma: preliminary findings. J Neuroradiol 2009; 36: Campbell JW, Pollack IF. Cerebellar astrocytomas in children. J Neurooncol 1996; 28: Gurney JG, Smith MA, Bunin GR. CNS and miscellaneous intracranial and intraspinal neoplasms. In: Ries LAG, Smith MA, Gurney JG, et al., eds. Cancer incidence and survival among children and adolescents: United States SEER Program Bethesda, MD: National Cancer Institute, 1999: NIH publication no Levy RA, Blaivas M, Murasko K, et al. Desmoplastic medulloblastoma: MR findings. AJNR 1997; 18: Koeller K, Rushing EJ. From the archives of the AFIP: medulloblastoma a comprehensive review with radiologic-pathologic correlation. RadioGraphics 2003; 23: Rumboldt Z, Camacho DL, Lake D, et al. Apparent diffusion coefficients for differentiation of cerebellar tumors in children. AJNR 2006; 27: Law M, Kazmi K, Wetzel S, et al. Dynamic susceptibility contrast-enhanced perfusion and conventional MR imaging findings for adult patients with cerebral primitive neuroectodermal tumors. AJNR 2004; 25: Nelson M, Diebler C, Forbes WS. Paediatric medul- AJR:200, May

10 Plaza et al. loblastoma: atypical CT features at presentation in the SIOP II Trial. Neuroradiology 1991; 33: Kumar R, Achari G, Banerjee D, et al. Uncommon presentation of medulloblastoma. Childs Nerv Syst 2001; 17: Panigrahy A, Bluml S. Neuroimaging of pediatric brain tumors: from basic to advanced MRI. J Child Neurol 2009; 24: Khong PL, Kwong DL, Chan GC, et al. Diffusiontensor imaging for the detection and quantification of treatment-induced white matter injury in children with medulloblastoma: a pilot study. AJNR 2003; 24: Mabbott DJ, Noseworthy MD, Bouffet E, Rockel C, Laughlin S. Diffusion tensor imaging of white matter after cranial radiation in children for medulloblastoma: correlation with IQ. Neuro Oncol 2006; 8: Tarbell NJ, Loeffler JS, Silver B, et al. The change in patterns of relapse of medulloblastoma. Cancer 1991; 68: Packer RJ, Gajjar A, Vezina G, et al. Phase III study of craniospinal radiation therapy followed by adjuvant chemotherapy for newly diagnosed average-risk medulloblastoma. J Clin Oncol 2006; 24: Gajjar A, Hernan R, Kocak M, et al. Clinical, histopathologic, and molecular markers of prognosis: toward a new disease risk stratification system for medulloblastoma. J Clin Oncol 2004; 22: Louis DN, Ohgaki H, Wiestler OD, et al. The 2007 WHO classification of tumours of the central nervous system. Acta Neuropathol 2007; 114: Meyers SP, Khademian ZP, Biegel JA, Chuang SH, Korones DN, Zimmerman RA. Primary intracranial atypical teratoid/rhabdoid tumors of infancy and childhood: MRI features and patient outcomes. AJNR 2006; 27: Arslanoglu A, Aygun N, Tekhtain D, et al. Imaging findings of CNS atypical teratoid/rhabdoid tumors. AJNR 2004; 25: Chi SN, Zimmerman MA, Yao X, et al. Intensive multimodality treatment for children with newly diagnosed CNS atypical teratoid rhabdoid tumor. J Clin Oncol 2009; 27: Koral K, Gargan L, Bowers DC, et al. Imaging characteristics of atypical teratoid-rhabdoid tumor in children compared with medulloblastoma. AJR 2008; 190: Yuh EL, Barkovich AJ, Gupta N. Imaging of ependymomas: MRI and CT. Childs Nerv Syst 2009; 25: Tihan T, Zhou T, Holmes E, Burger PC, Ozuysal S, Rushing EJ. The prognostic value of histological grading of posterior fossa ependymomas in children: a Children s Oncology Group study and a review of prognostic factors. Mod Pathol 2008; 21: Farwell JR, Dohrmann GJ, Flannery JT. Central nervous system tumors in children. Cancer 1977; 40: Panitch HS. Brain stem tumors of childhood and adolescence. Am J Dis Child 1970; 119: Freeman CR. Pediatric brainstem gliomas: a review. Int J Radiat Oncol Biol Phys 1998; 40: Farmer JP, Montes JL, Freeman CR, et al. Brainstem gliomas: a 10 year institutional review. Pediatr Neurosurg 2001; 34: Ullrich NJ, Raja AI, Irons MB, et al. Brainstem lesions in neurofibromatosis type 1. Neurosurgery 2007; 61: ; discussion, Moghrabi A, Kerby T, Tien RD, et al. Prognostic value of contrast-enhanced magnetic resonance imaging in brainstem gliomas. Pediatr Neurosurg 1995; 23: Poussaint TY, Kocak M, Vajapeyam S, et al. MRI as a central component of clinical trials analysis in brainstem glioma: a report from the Pediatric Brain Tumor Consortium (PBTC). Neuro Oncol 2011; 13: Löbel U, Sedlacik J, Reddick WE, et al. Quantitative diffusion-weighted and dynamic susceptibility-weighted contrast-enhanced perfusion MR imaging analysis of T2 hypointense lesion components in pediatric diffuse intrinsic pontine glioma. AJNR 2011; 32: Seymour ZA, Panigrahy A, Finlay JL, Nelson MD Jr, Blüml S. Citrate in pediatric CNS tumors? AJNR 2008; 29: Giussani C, Poliakov A, Ferri RD, et al. DTI fiber tracking to differentiate demyelinating diseases from diffuse brainstem glioma. Neuroimage 2010; 52: Frappaz D, Schell M, Thiesse P, et al. Preradiation chemotherapy may improve survival in pediatric diffuse intrinsic brainstem gliomas: final results of BSG 98 prospective trial. Neuro Oncol 2008; 10: Bowers DC, Georgiades C, Aronson LJ, et al. Tectal gliomas: natural history of an indolent lesion in pediatric patients. Pediatr Neurosurg 2000; 32: Vandertop WP, Hoffman HJ, Drake JM, et al. Focal midbrain tumors in children. Neurosurgery 1992; 31: Prabhu SP, Ng S, Vajapeyam S, et al. DTI assessment of the brainstem white matter tracts in pediatric BSG before and after therapy: a report from the Pediatric Brain Tumor Consortium. Childs Nerv Syst 2011; 27: Fisher PG, Tontiplaphol A, Pearlman EM, et al. Childhood cerebellar hemangioblastoma does not predict germline or somatic mutations in von Hippel-Lindau tumor suppressor gene. Ann Neurol 2002; 51: Leung RS, Biswas SV, Duncan M, Rankin S. Imaging features of von Hippel-Lindau disease. RadioGraphics 2008; 28:65 79; quiz, Ho VB, Smirniotopoulos, Murphy FM, Rushing EJ. Radiologic-pathologic correlation: hemangioblastoma. AJNR 1992; 13: Cho SK, Na DG, Ryoo JW, et al. Perfusion MR imaging: clinical utility for the differential diagnosis of various brain tumors. Korean J Radiol 2002; 3: Hasselblatt M, Jeibmann A, Gerss J, et al. Cellular and reticular variants of haemangioblastoma revisited: a clinicopathologic study of 88 cases. Neuropathol Appl Neurobiol 2005; 31: Poussaint TY. Magnetic resonance imaging of pediatric brain tumors: state of the art. Top Magn Reson Imaging 2001; 12: Castillo M, Smith JK, Kwock L. Correlation of myo-inositol levels and grading of cerebral astrocytomas. AJNR 2000; 21: Sener RN. Proton MR spectroscopy of craniopharyngiomas. Comput Med Imaging Graph 2001; 25: Salmela MB, Cauley KA, Andrews T, et al. Magnetic resonance diffusion tensor imaging of the optic nerves to guide treatment of pediatric suprasellar tumors. Pediatr Neurosurg 2009; 45: Lee HS, Seol HJ, Kong DS, Shin HJ. Moyamoya syndrome precipitated by cranial irradiation for craniopharyngioma in children. J Korean Neurosurg Soc 2011; 50: Saleem SN, Said AH, Lee DH. Lesions of the hypothalamus: MR imaging diagnostic features. RadioGraphics 2007; 27: Booth TN, Timmons C, Shapiro K, et al. Pre- and postnatal MR imaging of hypothalamic hamartomas associated with arachnoid cysts. AJNR 2004; 25: Jost SC, Ackerman JW, Garbow JR, Manwaring LP, Gutmann DH, McKinstry RC. Diffusionweighted and dynamic contrast-enhanced imaging as markers of clinical behavior in children with optic pathway glioma. Pediatr Radiol 2008; 38: FOR YOUR INFORMATION This article is available for CME/SAM credit. To access the exam for this article, follow the prompts associated with the online version of the article AJR:200, May 2013