DOI: 10.1148/rg.236035168
(Radiographics. 2003;23:1613-1637.)
From the Archives of the AFIP
Medulloblastoma: A Comprehensive Review with Radiologic-Pathologic Correlation1
Kelly K. Koeller, CAPT, MC, USN and
Elisabeth J. Rushing, COL, MC, USA
1 From the Departments of Radiologic Pathology (K.K.K.) and Neuropathology (E.J.R.), Armed Forces Institute of Pathology, 14th St at Alaska Ave, Bldg 54, Washington, DC 20306-6000; Departments of Radiology and Nuclear Medicine, Uniformed Services University of the Health Sciences, Bethesda, Md (K.K.K.); and Department of Pathology, George Washington University, Washington, DC (E.J.R.). Received July 17, 2003; revision requested July 30 and received August 14; accepted August 15. Address correspondence to K.K.K. (e-mail: koeller@afip.osd.mil).
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Abstract
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Medulloblastoma is the most common pediatric central nervous system malignancy and the most common primary tumor of the posterior fossa in children. This highly malignant neoplasm occurs more frequently in males and usually before 10 years of age. Clinical symptoms and signs are generally brief, typically less than 3 months in duration, and reflect the strong predilection of this tumor to arise within the cerebellum, most often in the vermis. Although much less common, the disease may also occur in adults, usually in the 3rd and 4th decades of life. Surgical resection, radiation therapy, and chemotherapy have substantially lowered the mortality associated with this tumor, with 5-year survival rates now commonly well above 50%. Still, both dissemination at the time of diagnosis and recurrence remain obstacles in achieving a cure. The tumor has characteristic hyperattenuation on unenhanced computed tomographic scans that reflects the high nuclear-cytoplasmic ratio seen at histologic analysis. The tumor typically appears heterogeneous on images, findings that are related to cyst formation, hemorrhage, and calcification and that are even more pronounced with magnetic resonance (MR) imaging. Evidence of leptomeningeal metastatic spread is present in 33% of all cases at the time of diagnosis and is well evaluated with contrast-enhanced MR imaging of the brain and the spine. Although controversial, postoperative surveillance with MR imaging is performed at most institutions in the hope of facilitating a better outcome. With continued research, treatment of these common neoplasms should improve, perhaps even achieving a cure in the future.
Index Terms: Brain neoplasms, 153.3637 • Medulloblastoma, 153.3637 • Neoplasms, in infants and children, 153.3637
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LEARNING OBJECTIVES FOR TEST 6
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After reading this article and taking the test, the reader will be able to:
- Recognize the distinguishing imaging features of medulloblastoma.
- Identify the characteristic imaging appearances of medulloblastoma in children and adults, including the presence of dissemination.
- Describe the direct correlation of the imaging appearance of medulloblastoma with its gross pathologic and histologic appearance.
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Introduction
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In the 78 years since the initial report, few neoplasms have been debated and scrutinized in the world’s literature as much as the medulloblastoma. With a near 100% mortality rate initially, it represented a neurosurgeon’s worst nightmare— an aggressive neoplasm located in one of the most challenging sites in a young child, who is almost certain to die from the disease within a matter of months or less. From these stark beginnings, substantial improvement in survival has been made because of a combination of several factors: (a) the implementation of radiation therapy to counter the rapid growth of the tumor; (b) improvements in neurosurgical equipment and technique that allowed greater accessibility to the posterior fossa and permitted a greater chance of gross total surgical resection; (c) the development of chemotherapy protocols that strive to optimize prevention of recurrence and minimize the chance of metastatic dissemination; and (d) the advent of modern cross-sectional imaging techniques, especially magnetic resonance (MR) imaging, that have completely changed the method of assessment for follow-up in affected patients.
Using case material from the Thompson Archives of the Department of Radiologic Pathology at the Armed Forces Institute of Pathology, we present the spectrum of cross-sectional imaging manifestations of this common tumor and a comprehensive summation of the history, pertinent clinical findings, pathologic characteristics, histogenesis, and prognosis associated with this tumor. Salient demographic and imaging features of medulloblastoma are listed in Table 1.
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Epidemiologic Characteristics
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Medulloblastoma is a highly malignant neuroepithelial tumor of the posterior fossa that is predominantly seen in children but may also occur in adults (1,2). Although it accounts for 6%–8% of all central nervous system tumors and 12%–25% of such tumors in the pediatric age group, it constitutes only 0.4%–1% of all adult central nervous system tumors (1,3–6). Medulloblastoma is the most common malignant central nervous system tumor in children and the second most common pediatric brain neoplasm, following only astrocytoma. It accounts for up to 38% of all pediatric posterior fossa tumors and represents the most common pediatric posterior fossa tumor overall (7,8).
From the single largest collection (532 cases) of medulloblastoma as part of the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) program, boys are more commonly affected (61.5%) (1). The overall mean age at diagnosis for all age groups is about 13 years (median age, 9 years), with most (77.4%) patients presenting before 19 years of age (1). Within this younger group of patients, the mean age at diagnosis is 7.3 years with small peaks at 3 years and 7 years (1). When medulloblastoma occurs in "adults," variably described in the literature as those older than 15–18 years of age, most (63%) manifest in patients 20–40 years of age (9,10). It is rare in patients older than 50 years of age, and the oldest patient on record was 73 years old at the time of diagnosis (9–11). Occasional familial cases have been reported (12). First-degree relatives of patients with medulloblastoma also appear to have increased rates of cancer (4).
By far, the cerebellum is the most common location for medulloblastomas (94.4% of cases in the SEER study), and most (>75%) of these arise in the midline cerebellar vermis (1,2). More lateral locations within the cerebellar hemisphere are typical when these tumors manifest in older children, adolescents, and adults. This difference in location is thought to be related to the migration of undifferentiated cells from the posterior medullary velum in a lateral and superior direction (1,5). Early in life, these cells are still located close to the midline and theoretically would give rise to midline tumors in the cerebellar vermis. Later in life, the cells have migrated further laterally, and, accordingly, the tumors that arise during this period of time would be expected to be within the cerebellar hemisphere, away from midline (13). Brain stem infiltration is common (33% of 144 cases in a series reported by Park et al) (14). Other less common locations include the fourth ventricle (3% of cases), other areas of the brain (2.1%), and the spinal cord (0.6%) (1).
The reported incidence of medulloblastoma ranges from one per 178,000 to one per 201,000 children aged 19 years or younger (4). From the Connecticut Tumor Registry, the prevalence of the tumor was noted to increase in the late 1950s and early 1960s, only to return to its baseline level thereafter (4). It is speculated that polio vaccine, containing the neoplasm-inducing papovavirus simian virus 40 from 1955 to 1961, may have played a role in the increased prevalence during this interval (4). Curiously, one report noted a seasonal increased prevalence, peaking in July, August, September, and October, based on the birth month of patients with medulloblastoma (15).
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Clinical Characteristics
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Typical clinical histories are usually brief and reflect the aggressive biologic behavior of the tumor. Most (75%) patients have symptoms for less than 3 months (14,16). Headache (generalized or localized to the suboccipital region) and persistent vomiting (without or with nausea) are common symptoms (14,16). Seizure activity is uncommon and may herald metastatic spread (16). Truncal ataxia, secondary to destruction of the cerebellar vermis, is the most common objective clinical sign and is frequently accompanied by spasticity (14,16). Other common clinical signs include papilledema (related to hydrocephalus), nystagmus, limb ataxia, and dysdiadokokinesis, with the last two findings reflecting a more laterally located mass within the cerebellar hemisphere (14,16). One-third of patients have positive Babinski and Hoffmann signs (16). Abducens nerve palsy, resulting from compression of the relatively exposed nucleus of the sixth cranial nerve along the anterior margin of the fourth ventricle, is also a common manifestation of the extraventricular tumor extension (16). Rare clinical findings include sudden neurologic deterioration and death secondary to acute hemorrhage into a medulloblastoma and spinal cord compression resulting from diffuse cerebrospinal fluid (CSF) seeding (14,16,17).
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Therapy
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Surgical resection and reestablishment of normal CSF flow remain the cornerstones of treatment of medulloblastoma in virtually all cases (1). With numerous technical improvements in neurosurgical techniques, equipment, and postoperative care and the development of a reliable operative staging system in 1969 (Table 2), the overalloperative mortality rate associated with these predominantly posterior fossa masses has plummeted from 50% in the mid-1900s to less than 10% today (16,18,19).
The tumor is very radiosensitive, and radiation therapy has been used since Bailey and Cushing (20) documented the initial cases. Not surprisingly, the combination of surgery and radiation therapy is most commonly used (1). The institution of presymptomatic craniospinal radiation therapy is probably the single most important factor responsible for the improved survival rates in these patients compared with those in the 1960s and early 1970s (1–4,14,21). Currently, radiation doses of 54 Gy to the posterior fossa, 30–36 Gy to the whole brain, and 26–32 Gy to the spine are typically employed in fractionated form (22–25).
Unfortunately, radiation therapy is not without substantial side effects. Radiation therapy has been implicated in the development of telangiectasia or cavernous malformation, which is easily detected on conventional T2-weighted MR images as focal hypointense regions confined to the radiated field (26–28). Because radiation therapy induces luminal narrowing that leads to increased venous pressure and occlusion, it is believed that venous restrictive disease is the most likely cause for development of these vascular malformations (28). On the arterial side, radiation injury induces hyalinization and fibrinoid necrosis within small arteries and arterioles, which leads to endothelial proliferation and occlusion (26,27). Although more commonly seen in patients receiving chemotherapy (eg, methotrexate), even mineralizing microangiopathy may occur in patients treated with radiation therapy alone (29).
Even more serious is radiation therapy’s staggering effect on the immature developing central nervous system of a young child. Impaired cognitive function, intellectual deterioration, and growth retardation are seen in virtually all treated patients in this group (14,24). Atrophy, especially of the posterior portions of the corpus callosum, is seen in over half of the cases (51%) (29,30). Calcification (28% of cases) and white matter abnormalities (26%) are also common, particularly in patients younger than 3 years of age (29,31). Consequently, craniospinal radiation therapy is strictly avoided in children younger than 2 years of age unless there is documented evidence of CSF dissemination or recurrence (21,32).
Since the 1980s, the role of adjuvant chemotherapy in the treatment of childhood medulloblastoma has steadily increased for several reasons. The use of either preoperative or postoperative chemotherapy is associated with an increase in survival rates in high-risk children with medulloblastoma (ie, those with fourth ventricle invasion and children less than 2 years of age) and in patients with recurrent or advanced disease (1,33). It also allows a reduction in the radiation therapy dose to the whole brain and spinal cord in patients with nondisseminated disease and is used to delay the onset of radiation therapy in young children (32,34,35). It is highly likely that the role of chemotherapy in the treatment of this tumor will expand and be refined in the future (25,36). The role of adjuvant postoperative therapy in adult patients with the disease is less certain, as both standard-risk and poor-risk patients have approximately the same rate of disease-free survival (37).
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Pathologic Characteristics
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At gross inspection, medulloblastomas have a variable appearance. Some are firm and discrete masses, whereas others may be soft and less well defined (Fig 1) (2). On occasion, prominent hemorrhage may also occur (2).
The World Health Organization classifies medulloblastoma as a grade IV lesion and recognizes four major subtypes of the tumor: classic, desmoplastic, extensively nodular with advanced neuronal differentiation, and large cell (2). Other less common subtypes include medullomyoblastoma and melanotic medulloblastoma (10,38).
The classic subtype is defined by dense, sheetlike growth of cells with hyperchromatic round-to-oval nuclei accompanied by increased mitotic activity and conspicuous apoptosis (Fig 2) (2). Areas of necrosis are less common. Neuroblastic or Homer-Wright rosettes, consisting of neoplastic cell nuclei disposed in a radial arrangement around fibrillary processes, are common features (2).
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Figure 2. Classic medulloblastoma. Photomicrograph (original magnification, x400; hematoxylin-eosin stain) of a classic medulloblastoma reveals monomorphic sheets of closely apposed small cells with a high nuclear-cytoplasmic ratio, occasionally interrupted by neuroblastic rosettes (arrows).
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The desmoplastic subtype is characterized by nodular reticulin-free "pale islands" that are surrounded by reticulin-staining collagen fibers (Fig 3) (2). This tumor subtype was originally described as a "circumscribed arachnoidal cerebellar sarcoma," a term that is now obsolete (39).
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Figure 3. Desmoplastic-nodular medulloblastoma. Photomicrograph (original magnification x400; hematoxylin-eosin stain) of a desmoplastic-nodular medulloblastoma shows a prominent nodule, or "pale island," (I) containing small, uniform neurocytic cells with abundant cytoplasm. Smaller pale islands surround the dominant nodule. The internodular zones often contain abundant reticulin and are populated by more atypical cells.
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A third subtype—"medulloblastoma with extensive nodularity and advanced neuronal differentiation"—occurs primarily in children less than 3 years of age and is associated with a "grapelike" nodularity seen on cross-sectional images (2). Intranodular cellular uniformity, accompanied by a fine fibrillary matrix and occasional mature ganglion cells, are typical. This variant is also known by the term cerebellar neuroblastoma (40).
Finally, the large cell medulloblastoma is the least common form (about 4% of cases). The salient morphologic features include large round nuclei with prominent nucleoli, nuclear molding, and abundant cytoplasm (Fig 4) (2). This form carries the poorest prognosis of the four major histologic subtypes (2). Some authorities have also reported an anaplastic type with some features similar to the large-cell variant including its poor prognosis (41). Accordingly, it is sometimes called the "large cell–anaplastic" variant (42).
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Figure 4. Large cell-anaplastic medulloblastoma. Photomicrograph (original magnification x400; hematoxylin-eosin stain) of a large cell-anaplastic medulloblastoma demonstrates characteristic cells with large nuclei containing prominent nucleoli (arrowheads), accompanied by conspicuous apoptosis and numerous mitoses.
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As debate continues among neuropathologists, some authorities have merged some of these subtypes into hybrid forms based on their morphologic similarity and comparable clinical outcome. This has led to the description of a "nodular/desmoplastic" form, "medulloblastoma with neuroblastic or neuronal differentiation," and even "medulloblastoma with glial differentiation" (41,42). It is clear that the naming and categorization of these tumors is an evolving process, and more data and discussion are likely required to reach a consensus about the nomenclature of these lesions.
The entity previously known as "lipomatous medulloblastoma" is now designated "cerebellar liponeurocytoma" (43). The World Health Organization working group considers this lesion a distinct clinicopathologic entity with an overall good prognosis. In contrast to medulloblastoma, this low-grade neuronal tumor usually occurs in much older patients (range, 36–67 years) and does not require adjuvant postoperative therapy in most, if not all, cases (44). This lesion has a distinctive imaging appearance, being seen on cross-sectional images as a cerebellar mass containing areas of attenuation or signal intensity similar to those of fat (45).
A plethora of chromosomal abnormalities has been identified in medulloblastomas. The most common (30%–45% of cases) is the loss of genetic material from chromosomal arm 17p (46). This site is apparently the location of a suppressor gene, the removal of which allows for the expression of the tumor (46). Absence of this structure has also been linked with medulloblastomas with aggressive biologic behavior compared with those medulloblastomas without this genetic loss (47). Other identified chromosomal abnormalities in medulloblastomas, by either gains or losses, include chromosomes 1, 8, 9, 10, 11, and 16 (47).
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Histogenesis
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The cell of origin for a medulloblastoma has been controversial since Bailey and Cushing (20) first described the initial 29 cases in 1925 and noted its affinity to grow from the roof of the fourth ventricle. They hypothesized that the tumor arose from a "medulloblast," an undifferentiated embryonal cell located in the external granular layer of the cerebellum that could then give rise to other formative cells. Although an attractive theory in its time, no neuroanatomic proof of this cell was ever identified, and the theory was subsequently abandoned (2).
The three existing theories of medulloblastoma histogenesis also focus on the concept of an undifferentiated cell with the capacity to differentiate into other cell lines (2). The first proposes that the external granular layer itself is the site of origin. Cells located along the roof of the fourth ventricle and posterior medullary velum migrate laterally and upward to form this layer. This theory is supported by the observation of certain gene mutations in sporadic medulloblastoma that are also responsible for control of developing neurons in this layer and by the observation of neuronal differentiation in some medulloblastomas (1,13,48,49).
The second theory espouses the concept that all medulloblastomas are actually primitive neuroectodermal tumors (PNETs). This theory is supported by the observation that many medulloblastomas share common histologic features with supratentorial PNETs (50). However, recent investigations have revealed genetic differences between the two tumor types, casting some doubt on this theory (2).
The third hypothesis proposes that medulloblastomas may have more than one cell of origin. This theory is supported by the expression of immunoreactivity in two different cell types, one that is found associated with the developing ventricular system and the other that is found in cells derived from both the ventricular matrix and the external granular layer. It is proposed that this theory could account for the classic medulloblastoma arising from the ventricular matrix cell line, whereas desmoplastic medulloblastomas arise from the external granular layer (2).
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Imaging Features
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Computed Tomography
The classic computed tomographic (CT) appearance of a medulloblastoma is a hyperattenuated, well-defined vermian cerebellar mass with surrounding vasogenic edema, evidence of hydrocephalus, and homogeneous enhancement on contrast material–enhanced images in a child less than 10 years of age (Figs 5, 6) (16,51,52). From data collected on 420 patients in three studies, 89% of all medulloblastomas demonstrated at least some hyperattenuation compared with normal cerebellar attenuation on nonenhanced CT scans (16,51,53). In a review of 233 patients, Nelson et al (53) found that 95% had marginal vasogenic edema and 97% had at least some enhancement (Fig 5). However, variance from this imaging appearance is common, seen in about 40% of all cases (51,53,54). Cyst formation (59% of cases) and calcification (22%) (Figs 7, 8) were common in the study by Nelson et al (53). Other less common atypical features include ill-defined margins, absence of vasogenic edema or hydrocephalus, hypoattenuation, hemorrhage, absence of enhancement on contrast-enhanced images, and the appearance of "primary" leptomeningeal dissemination (Fig 9) (16,51,53,54,56).
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Figure 5a. Medulloblastoma in a 6-year-old girl with a 10-day history of nausea and vomiting. (a) Axial CT image shows a heterogeneous hyperattenuated mass in the right cerebellar hemisphere. (b) On an axial T1-weighted MR image, the mass has homogeneous hypointensity compared with normal cerebellar signal intensity. (c) On an axial T2-weighted MR image, the mass is heterogeneous with surrounding vasogenic edema. (d) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement of the mass.
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Figure 5b. Medulloblastoma in a 6-year-old girl with a 10-day history of nausea and vomiting. (a) Axial CT image shows a heterogeneous hyperattenuated mass in the right cerebellar hemisphere. (b) On an axial T1-weighted MR image, the mass has homogeneous hypointensity compared with normal cerebellar signal intensity. (c) On an axial T2-weighted MR image, the mass is heterogeneous with surrounding vasogenic edema. (d) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement of the mass.
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Figure 5c. Medulloblastoma in a 6-year-old girl with a 10-day history of nausea and vomiting. (a) Axial CT image shows a heterogeneous hyperattenuated mass in the right cerebellar hemisphere. (b) On an axial T1-weighted MR image, the mass has homogeneous hypointensity compared with normal cerebellar signal intensity. (c) On an axial T2-weighted MR image, the mass is heterogeneous with surrounding vasogenic edema. (d) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement of the mass.
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Figure 5d. Medulloblastoma in a 6-year-old girl with a 10-day history of nausea and vomiting. (a) Axial CT image shows a heterogeneous hyperattenuated mass in the right cerebellar hemisphere. (b) On an axial T1-weighted MR image, the mass has homogeneous hypointensity compared with normal cerebellar signal intensity. (c) On an axial T2-weighted MR image, the mass is heterogeneous with surrounding vasogenic edema. (d) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement of the mass.
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Figure 6a. Medulloblastoma in a 3-year-old boy with a 1-month history of progressively worsening clumsiness, ataxia, headache, nausea, and vomiting. Developmental delay in speech and motor skills was also present. Papilledema was noted on physical examination. (a) Axial CT image shows a nearly homogeneous hyperattenuated mass in the posterior fossa midline. A thin crescent of the fourth ventricle (arrowheads) is noted along the anterior margin of the mass. (b) On an axial T1-weighted MR image, the mass is hypointense compared with the surrounding normal cerebellum. (c) On an axial T2-weighted MR image, the mass shows mild hyperintensity compared with surrounding normal brain tissue. (d) Contrast-enhanced axial T1-weighted MR image shows intense but mildly heterogeneous enhancement of the mass. (e) Photograph of the resected specimen highlights the soft friable nature of the mass, characteristic of a medulloblastoma.
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Figure 6b. Medulloblastoma in a 3-year-old boy with a 1-month history of progressively worsening clumsiness, ataxia, headache, nausea, and vomiting. Developmental delay in speech and motor skills was also present. Papilledema was noted on physical examination. (a) Axial CT image shows a nearly homogeneous hyperattenuated mass in the posterior fossa midline. A thin crescent of the fourth ventricle (arrowheads) is noted along the anterior margin of the mass. (b) On an axial T1-weighted MR image, the mass is hypointense compared with the surrounding normal cerebellum. (c) On an axial T2-weighted MR image, the mass shows mild hyperintensity compared with surrounding normal brain tissue. (d) Contrast-enhanced axial T1-weighted MR image shows intense but mildly heterogeneous enhancement of the mass. (e) Photograph of the resected specimen highlights the soft friable nature of the mass, characteristic of a medulloblastoma.
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Figure 6c. Medulloblastoma in a 3-year-old boy with a 1-month history of progressively worsening clumsiness, ataxia, headache, nausea, and vomiting. Developmental delay in speech and motor skills was also present. Papilledema was noted on physical examination. (a) Axial CT image shows a nearly homogeneous hyperattenuated mass in the posterior fossa midline. A thin crescent of the fourth ventricle (arrowheads) is noted along the anterior margin of the mass. (b) On an axial T1-weighted MR image, the mass is hypointense compared with the surrounding normal cerebellum. (c) On an axial T2-weighted MR image, the mass shows mild hyperintensity compared with surrounding normal brain tissue. (d) Contrast-enhanced axial T1-weighted MR image shows intense but mildly heterogeneous enhancement of the mass. (e) Photograph of the resected specimen highlights the soft friable nature of the mass, characteristic of a medulloblastoma.
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Figure 6d. Medulloblastoma in a 3-year-old boy with a 1-month history of progressively worsening clumsiness, ataxia, headache, nausea, and vomiting. Developmental delay in speech and motor skills was also present. Papilledema was noted on physical examination. (a) Axial CT image shows a nearly homogeneous hyperattenuated mass in the posterior fossa midline. A thin crescent of the fourth ventricle (arrowheads) is noted along the anterior margin of the mass. (b) On an axial T1-weighted MR image, the mass is hypointense compared with the surrounding normal cerebellum. (c) On an axial T2-weighted MR image, the mass shows mild hyperintensity compared with surrounding normal brain tissue. (d) Contrast-enhanced axial T1-weighted MR image shows intense but mildly heterogeneous enhancement of the mass. (e) Photograph of the resected specimen highlights the soft friable nature of the mass, characteristic of a medulloblastoma.
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Figure 6e. Medulloblastoma in a 3-year-old boy with a 1-month history of progressively worsening clumsiness, ataxia, headache, nausea, and vomiting. Developmental delay in speech and motor skills was also present. Papilledema was noted on physical examination. (a) Axial CT image shows a nearly homogeneous hyperattenuated mass in the posterior fossa midline. A thin crescent of the fourth ventricle (arrowheads) is noted along the anterior margin of the mass. (b) On an axial T1-weighted MR image, the mass is hypointense compared with the surrounding normal cerebellum. (c) On an axial T2-weighted MR image, the mass shows mild hyperintensity compared with surrounding normal brain tissue. (d) Contrast-enhanced axial T1-weighted MR image shows intense but mildly heterogeneous enhancement of the mass. (e) Photograph of the resected specimen highlights the soft friable nature of the mass, characteristic of a medulloblastoma.
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Figure 7a. Medulloblastoma in a 4-year-old boy with a 2-week history of headaches and vomiting. (a) Axial CT image shows a heterogeneous mass in the posterior fossa midline. Soft-tissue portions are hyperattenuated whereas more cystlike areas are hypoattenuated. (b) On an axial T1-weighted MR image, the mass has similar heterogeneity. (c) Axial T2-weighted MR image demonstrates mild hyperintensity of the soft-tissue section and marked hyperintensity of the cystlike compartment. Note that the signal intensity of the cystlike portion (arrows) is even more intense than that of CSF, indicating that it is not simple fluid. (d) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement within the soft-tissue segment.
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Figure 7b. Medulloblastoma in a 4-year-old boy with a 2-week history of headaches and vomiting. (a) Axial CT image shows a heterogeneous mass in the posterior fossa midline. Soft-tissue portions are hyperattenuated whereas more cystlike areas are hypoattenuated. (b) On an axial T1-weighted MR image, the mass has similar heterogeneity. (c) Axial T2-weighted MR image demonstrates mild hyperintensity of the soft-tissue section and marked hyperintensity of the cystlike compartment. Note that the signal intensity of the cystlike portion (arrows) is even more intense than that of CSF, indicating that it is not simple fluid. (d) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement within the soft-tissue segment.
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Figure 7c. Medulloblastoma in a 4-year-old boy with a 2-week history of headaches and vomiting. (a) Axial CT image shows a heterogeneous mass in the posterior fossa midline. Soft-tissue portions are hyperattenuated whereas more cystlike areas are hypoattenuated. (b) On an axial T1-weighted MR image, the mass has similar heterogeneity. (c) Axial T2-weighted MR image demonstrates mild hyperintensity of the soft-tissue section and marked hyperintensity of the cystlike compartment. Note that the signal intensity of the cystlike portion (arrows) is even more intense than that of CSF, indicating that it is not simple fluid. (d) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement within the soft-tissue segment.
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Figure 7d. Medulloblastoma in a 4-year-old boy with a 2-week history of headaches and vomiting. (a) Axial CT image shows a heterogeneous mass in the posterior fossa midline. Soft-tissue portions are hyperattenuated whereas more cystlike areas are hypoattenuated. (b) On an axial T1-weighted MR image, the mass has similar heterogeneity. (c) Axial T2-weighted MR image demonstrates mild hyperintensity of the soft-tissue section and marked hyperintensity of the cystlike compartment. Note that the signal intensity of the cystlike portion (arrows) is even more intense than that of CSF, indicating that it is not simple fluid. (d) Contrast-enhanced axial T1-weighted MR image shows heterogeneous enhancement within the soft-tissue segment.
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Figure 8. Medulloblastoma in a 10-year-old boy. Axial CT image shows a heterogeneous hyperattenuated mass in the midline of the posterior fossa. Focal areas of hyperattenuation (arrows) represent calcification, an occasional manifestation of this disease. (Reprinted, with permission, from reference 55.)
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Figure 9a. Medulloblastoma in a 4-year-old boy with a 2-month history of ataxic gait. On day of admission, he hit his head on the floor and presented comatose to the emergency department. (a) Axial CT image shows a heterogeneous mass in the cerebellar vermis. Areas of hyperattenuation (arrowheads) are secondary to hemorrhage. The fourth ventricle is not seen. (b) Axial T1-weighted MR image shows mild hyperintensity in the hemorrhagic regions; otherwise the mass is predominantly hypointense. (c) Axial T2-weighted MR image reveals marked hypointensity in the hemorrhagic zones. These features are consistent with intracellular methemoglobin. (d) Contrast-enhanced axial T1-weighted MR image demonstrates heterogeneous but intense enhancement of the nonhemorrhagic portions. (e) Sagittal T1-weighted MR image shows complete filling of the fourth ventricle and upward extension of the posterior fossa mass through the cerebral aqueduct (arrow) into the third ventricle.
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Figure 9b. Medulloblastoma in a 4-year-old boy with a 2-month history of ataxic gait. On day of admission, he hit his head on the floor and presented comatose to the emergency department. (a) Axial CT image shows a heterogeneous mass in the cerebellar vermis. Areas of hyperattenuation (arrowheads) are secondary to hemorrhage. The fourth ventricle is not seen. (b) Axial T1-weighted MR image shows mild hyperintensity in the hemorrhagic regions; otherwise the mass is predominantly hypointense. (c) Axial T2-weighted MR image reveals marked hypointensity in the hemorrhagic zones. These features are consistent with intracellular methemoglobin. (d) Contrast-enhanced axial T1-weighted MR image demonstrates heterogeneous but intense enhancement of the nonhemorrhagic portions. (e) Sagittal T1-weighted MR image shows complete filling of the fourth ventricle and upward extension of the posterior fossa mass through the cerebral aqueduct (arrow) into the third ventricle.
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Figure 9c. Medulloblastoma in a 4-year-old boy with a 2-month history of ataxic gait. On day of admission, he hit his head on the floor and presented comatose to the emergency department. (a) Axial CT image shows a heterogeneous mass in the cerebellar vermis. Areas of hyperattenuation (arrowheads) are secondary to hemorrhage. The fourth ventricle is not seen. (b) Axial T1-weighted MR image shows mild hyperintensity in the hemorrhagic regions; otherwise the mass is predominantly hypointense. (c) Axial T2-weighted MR image reveals marked hypointensity in the hemorrhagic zones. These features are consistent with intracellular methemoglobin. (d) Contrast-enhanced axial T1-weighted MR image demonstrates heterogeneous but intense enhancement of the nonhemorrhagic portions. (e) Sagittal T1-weighted MR image shows complete filling of the fourth ventricle and upward extension of the posterior fossa mass through the cerebral aqueduct (arrow) into the third ventricle.
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Figure 9d. Medulloblastoma in a 4-year-old boy with a 2-month history of ataxic gait. On day of admission, he hit his head on the floor and presented comatose to the emergency department. (a) Axial CT image shows a heterogeneous mass in the cerebellar vermis. Areas of hyperattenuation (arrowheads) are secondary to hemorrhage. The fourth ventricle is not seen. (b) Axial T1-weighted MR image shows mild hyperintensity in the hemorrhagic regions; otherwise the mass is predominantly hypointense. (c) Axial T2-weighted MR image reveals marked hypointensity in the hemorrhagic zones. These features are consistent with intracellular methemoglobin. (d) Contrast-enhanced axial T1-weighted MR image demonstrates heterogeneous but intense enhancement of the nonhemorrhagic portions. (e) Sagittal T1-weighted MR image shows complete filling of the fourth ventricle and upward extension of the posterior fossa mass through the cerebral aqueduct (arrow) into the third ventricle.
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Figure 9e. Medulloblastoma in a 4-year-old boy with a 2-month history of ataxic gait. On day of admission, he hit his head on the floor and presented comatose to the emergency department. (a) Axial CT image shows a heterogeneous mass in the cerebellar vermis. Areas of hyperattenuation (arrowheads) are secondary to hemorrhage. The fourth ventricle is not seen. (b) Axial T1-weighted MR image shows mild hyperintensity in the hemorrhagic regions; otherwise the mass is predominantly hypointense. (c) Axial T2-weighted MR image reveals marked hypointensity in the hemorrhagic zones. These features are consistent with intracellular methemoglobin. (d) Contrast-enhanced axial T1-weighted MR image demonstrates heterogeneous but intense enhancement of the nonhemorrhagic portions. (e) Sagittal T1-weighted MR image shows complete filling of the fourth ventricle and upward extension of the posterior fossa mass through the cerebral aqueduct (arrow) into the third ventricle.
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The presence of falcine calcification in children with medulloblastoma may be a marker for nevoid basal cell carcinoma. Because patients with this tumor tend to develop numerous basal cell carcinomas in irradiated fields, scrutiny of CT studies in such patients is warranted, since it may affect therapeutic decisions in favor of chemotherapy or reduced-dose radiation therapy (57).
MR Imaging
At MR imaging, the typical appearance of a medulloblastoma is iso- to- hypointense relative to white matter with short repetition time/short echo time pulse sequences and variable signal intensity relative to white matter with long repetition time pulse sequences (58). Even greater degrees of heterogeneity among these lesions are described for those seen on MR images than on CT scans (58). As with CT, nearly all enhance following the intravenous administration of contrast material, but the enhancement is usually heterogeneous (Figs 10–13) (58). MR spectroscopy in cases of medulloblastoma typically shows elevated choline peaks, reduced N-acetyl aspartate and creatine peaks, and occasionally elevated lipid and lactic acid peaks, a characteristic spectrographic signature for a neuroectodermal tumor but not necessarily specific for medulloblastoma (59).
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Figure 10a. Medulloblastoma in a 6-year-old boy with recurrent headaches. (a) Axial T1-weighted MR image shows a heterogeneous soft-tissue mass (arrows) in the right cerebellar hemisphere with an associated peripheral cystlike region. The soft-tissue portion is hypointense relative to the normal cerebellum. Several focal areas of fluidlike hypointensity are noted within the mass. (b) Axial T2-weighted MR image shows that the soft-tissue component is slightly hyperintense relative to the normal cerebellum. The fluidlike areas are again noted. (c) Contrast-enhanced axial T1-weighted MR image demonstrates intense but heterogeneous enhancement of the soft-tissue portion. The nonenhancing regions represent either cystic degeneration or necrosis.
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Figure 10b. Medulloblastoma in a 6-year-old boy with recurrent headaches. (a) Axial T1-weighted MR image shows a heterogeneous soft-tissue mass (arrows) in the right cerebellar hemisphere with an associated peripheral cystlike region. The soft-tissue portion is hypointense relative to the normal cerebellum. Several focal areas of fluidlike hypointensity are noted within the mass. (b) Axial T2-weighted MR image shows that the soft-tissue component is slightly hyperintense relative to the normal cerebellum. The fluidlike areas are again noted. (c) Contrast-enhanced axial T1-weighted MR image demonstrates intense but heterogeneous enhancement of the soft-tissue portion. The nonenhancing regions represent either cystic degeneration or necrosis.
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Figure 10c. Medulloblastoma in a 6-year-old boy with recurrent headaches. (a) Axial T1-weighted MR image shows a heterogeneous soft-tissue mass (arrows) in the right cerebellar hemisphere with an associated peripheral cystlike region. The soft-tissue portion is hypointense relative to the normal cerebellum. Several focal areas of fluidlike hypointensity are noted within the mass. (b) Axial T2-weighted MR image shows that the soft-tissue component is slightly hyperintense relative to the normal cerebellum. The fluidlike areas are again noted. (c) Contrast-enhanced axial T1-weighted MR image demonstrates intense but heterogeneous enhancement of the soft-tissue portion. The nonenhancing regions represent either cystic degeneration or necrosis.
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Figure 11a. Medulloblastoma in a 4-month-old boy with irritability and vomiting. Physical examination revealed increased head circumference, bulging fontanelle, and left gaze preference. (a) Axial CT image shows a hyperattenuated heterogeneous mass in the midline of the posterior fossa with nearly complete effacement of adjacent cisternal spaces. (b) On an axial T1-weighted MR image, the mass is heterogeneous with focal areas of hyperintensity mixed with isointense signal. (c) On an axial T2-weighted MR image, the mass has mild hypointensity compared with gray matter and contains scattered areas of moderate hypointensity that correspond to regions of hemorrhage. (d) Contrast-enhanced sagittal MR image shows intense plaquelike enhancement of the mass with superior displacement of the straight sinus (arrowheads).
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Figure 11b. Medulloblastoma in a 4-month-old boy with irritability and vomiting. Physical examination revealed increased head circumference, bulging fontanelle, and left gaze preference. (a) Axial CT image shows a hyperattenuated heterogeneous mass in the midline of the posterior fossa with nearly complete effacement of adjacent cisternal spaces. (b) On an axial T1-weighted MR image, the mass is heterogeneous with focal areas of hyperintensity mixed with isointense signal. (c) On an axial T2-weighted MR image, the mass has mild hypointensity compared with gray matter and contains scattered areas of moderate hypointensity that correspond to regions of hemorrhage. (d) Contrast-enhanced sagittal MR image shows intense plaquelike enhancement of the mass with superior displacement of the straight sinus (arrowheads).
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Figure 11c. Medulloblastoma in a 4-month-old boy with irritability and vomiting. Physical examination revealed increased head circumference, bulging fontanelle, and left gaze preference. (a) Axial CT image shows a hyperattenuated heterogeneous mass in the midline of the posterior fossa with nearly complete effacement of adjacent cisternal spaces. (b) On an axial T1-weighted MR image, the mass is heterogeneous with focal areas of hyperintensity mixed with isointense signal. (c) On an axial T2-weighted MR image, the mass has mild hypointensity compared with gray matter and contains scattered areas of moderate hypointensity that correspond to regions of hemorrhage. (d) Contrast-enhanced sagittal MR image shows intense plaquelike enhancement of the mass with superior displacement of the straight sinus (arrowheads).
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Figure 11d. Medulloblastoma in a 4-month-old boy with irritability and vomiting. Physical examination revealed increased head circumference, bulging fontanelle, and left gaze preference. (a) Axial CT image shows a hyperattenuated heterogeneous mass in the midline of the posterior fossa with nearly complete effacement of adjacent cisternal spaces. (b) On an axial T1-weighted MR image, the mass is heterogeneous with focal areas of hyperintensity mixed with isointense signal. (c) On an axial T2-weighted MR image, the mass has mild hypointensity compared with gray matter and contains scattered areas of moderate hypointensity that correspond to regions of hemorrhage. (d) Contrast-enhanced sagittal MR image shows intense plaquelike enhancement of the mass with superior displacement of the straight sinus (arrowheads).
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Figure 12a. Medulloblastoma in a 10-month-old boy with nausea and vomiting for several months and recent onset of lethargy and failure to meet developmental milestones. (a) Axial CT image shows a heterogeneous mass involving the cerebellar vermis and hemisphere with extension toward the left cerebellopontine angle. The soft-tissue portion near midline is hyperattenuated, whereas the fluidlike compartment is more lateral and posterior in location. (b) Axial T1-weighted MR image reveals mild hypointensity of the soft-tissue portion with moderate hypointensity in the cystlike region. This latter signal intensity is more hyperintense relative to normal CSF, thereby indicating that it is not simple fluid but likely contains proteinaceous debris or possibly hemorrhage. The extension through the left foramen of Luschka (arrow) is bette | |
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Abstract
LEARNING OBJECTIVES FOR TEST...
