AUTHOR AND EDITOR INFORMATION

Section 1 of 12  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 12  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Background

Of primary brain tumors in children, one half originate in the posterior fossa. Medulloblastomas are highly malignant tumors representing the most common malignant posterior fossa tumor in the pediatric population. They are characterized by their tendency to seed along the neuraxis, following cerebrospinal fluid (CSF) pathways, and they represent one of the few brain tumors, including ependymoma, pinealoblastoma, and lymphoma, to metastasize to extraneural tissues. Originally classified as a glioma, medulloblastoma is now referred to as a primitive neuroectodermal tumor (PNET).

Of medulloblastoma patients, 10-30% demonstrate CSF dissemination at diagnosis, mandating evaluation of the entire neuraxis with contrast-enhanced studies. Extra-axial metastases account for 5% of cases; most metastases are to the bone, followed less frequently by the liver and lymph nodes.

Medulloblastomas have been associated with basal nevus syndrome (Gorlin syndrome), Turcot syndrome, ataxia telangiectasia, xeroderma pigmentosum, and blue rubber bleb syndrome.

Standard treatment is surgery followed by radiation to the entire neuraxis. Medulloblastomas are radiosensitive.

Pathophysiology

Medulloblastomas are believed to arise from the primitive neuroepithelial cells located in the roof of the 4th ventricle. These cells migrate outward and laterally to form the external granular layer of the cerebellum, which in normal circumstances involute by a gestational age of 18 months. Therefore, it is reasonable to presume that medulloblastomas can occur anywhere along the migratory pathway. Medulloblastomas are highly cellular, soft, and friable tumors with a deeply basophilic nucleus of variable size and shape, often with multiple mitoses. This histologic aspect is not particular to medulloblastomas, since other embryonal tumors (neuroblastoma, pineoblastoma) can exhibit the same appearance, constituting the primitive neuroectodermal tumor group.

Hyperdiploidy in tumor cells may represent a favorable factor, while an isochromosome of 17q appears to be unfavorable. Invasion of the leptomeninges through CSF pathways is frequent. Spinal drop metastases in the subarachnoid space are seen in approximately 40% of patients, most frequently at the level of the thoracic and lumbosacral spine. In rare instances, intramedullary metastases have been reported.

Frequency

United States

Medulloblastomas represent 15-20% of intracranial neoplasms and 30-40% of posterior fossa tumors in the pediatric population. In the adult population, medulloblastomas represent less than 1% of CNS neoplasms.

Mortality/Morbidity

Generally, the survival rate has improved markedly since the 25% rate reported in the 1960s. Current large series approximate 60% disease control. In selected experiences, aggressive postradiation chemotherapy demonstrated disease-free rates of 85% at 5 years, as reported by Kun.

Race

No racial predilection is noted.

Sex

Male-to-female ratio is 2-4:1 in most series.

Age

Medulloblastomas demonstrate a bimodal age distribution with a larger peak at age 2-8 years and a smaller peak at age 20-30 years.

Anatomy

Exclusively cerebellar, medulloblastomas typically arise from the cerebellar vermis and the roof of the fourth ventricle in the younger age group and, less commonly, from the cerebellar hemisphere in the older age group.

Clinical Details

Duration of symptoms usually is less than 1 month at diagnosis. Patients often present with clumsiness, loss of motor skills, diplopia, and dizziness.

On physical examination, cerebellar signs dominate. Morning headache, nausea, and vomiting occur in 70-90% of patients secondary to increased intracranial pressure. Seizures are rare.

Preferred Examination

Although the appearance of CT findings in medulloblastoma are highly characteristic, MRI is the preferred tool since its multiplanar capability provides better 3-dimensional appreciation of the tumor's extent, edema, and herniation when present. MRI also provides better evaluation for metastasis on the remainder of the neuraxis. In addition, MRI spectroscopy may help better delineate the tumor's boundaries.

Limitations of Techniques

On CT, only axial images can be obtained compared to MRI, in which any plane can be used for imaging. On CT, posterior fossa images often are degraded by beam-hardening artifacts.

DIFFERENTIALS

Section 3 of 12  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Other Problems to be Considered

Ependymoma
Astrocytoma
Meningioma

RADIOGRAPH

Section 4 of 12  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

No specific findings are seen on plain radiographs.

CT SCAN

Section 5 of 12  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

• Medulloblastomas are highly cellular tumors; therefore, their classic appearance on noncontrast CT is a high-density midline mass with, in most patients (90%), a varying degree of hydrocephalus.

• Variable amounts of asymmetric edema are seen in approximately 90% of patients.

• On enhanced CT, a marked homogeneous enhancement of the tumor is seen.

• In rare circumstances, calcifications can be found (13%).

• Metastatic nodular seeding may be seen in the supratentorial subarachnoid space on contrast enhanced CT and in the spinal canal on CT myelography.

• The presence of necrotic, cystic areas and hemorrhage is unusual and found in approximately 10-16% and 3% of patients, respectively.

Degree of Confidence

A high-density midline posterior fossa mass with diffuse marked enhancement in a child, especially boy, is highly suspicious for medulloblastoma.

CT is superior to MRI in depicting small punctate calcifications.

MRI

Section 6 of 12  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

• Medulloblastomas are hypointense to isointense on T1-weighted images.



• T2-weighted appearance can vary from isointense to hyperintense.



• Medulloblastomas classically demonstrate heterogeneous hypointense or isointense signal.



• Calcifications appear as signal void on T2-weighted images.



• The pattern of enhancement after intravenous injection of gadolinium is similar to that after injection of iodinated contrast material on CT. However, the greater sensitivity of MRI often enables appreciation of a slightly heterogenous enhancing pattern not as readily evident with CT.

  Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with troublemovingorstraightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.

• The blurring of cerebellar folia and fissures representing tumor spread via CSF pathways (best depicted on midline sagittal images) is a helpful sign. Subarachnoid or intraventricular seeding usually demonstrates contrast enhancement.



• Drop metastases appear as high signal foci on contrast-enhanced T1-weighted images in the extramedullary, intradural space and, occasionally, subpial in location.



• Proton spectroscopy demonstrates nonspecific elevation of the choline peak, translating cell membrane turnover; decreased aspartate peak, translating loss of neuronal tissue; and variable lipid and lactate.

Degree of Confidence

Because of the age group, location, and general appearance of the tumors, the degree of confidence usually is high with MRI.

ULTRASOUND

Section 7 of 12  

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• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

Ultrasound has no significant role in medulloblastoma.

NUCLEAR MEDICINE

Section 8 of 12  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

No specific findings are described; however, single-photon emission CT (SPECT) and positron emission tomography (PET) complement CT and MRI. Although the mechanism of uptake is not clearly understood, 80% of pediatric tumors show uptake of thallium-201 chloride (²⁰¹TI). These techniques also are important in differentiating high-grade from low-grade tumors and residual tumor from postoperative changes.

Degree of Confidence

Thallium SPECT and fluorine-18-flurodeoxyglucose PET are complementary in diagnosing gliomas, although thallium SPECT was found to correlate more significantly with malignancy. In a series of 19 patients, Kahn et al demonstrated that the sensitivity and specificity for tumor recurrence is 69% and 40%, respectively, for ²⁰¹TI and 81% and 40%, respectively, for PET.

ANGIOGRAPHY

Section 9 of 12  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

Angiogram findings are not diagnostic. Medulloblastoma may demonstrate abnormal neovascularity. Since it is a posterior fossa tumor, anterior displacement of the precentral cerebellar vein may be seen. Posterior and inferior displacement of the inferior vermian vein also may be seen.

Degree of Confidence

Angiographic findings are nonspecific for diagnosis and are only indicative of a space-occupying lesion.

INTERVENTION

Section 10 of 12  

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• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Gross total resection of the tumor, when possible, is the aim of surgery. Resection usually is achieved in 50% of patients, according to Thapar et al.

Surgery is followed by irradiation of the entire neuraxis: 54 Gy to the tumor bed, 35 Gy to the other areas of the brain, and 24 Gy to the spinal deposit.

MULTIMEDIA

Section 11 of 12  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Media file 1:  Medulloblastoma. Unenhanced CT shows a high-density midline tumor in the posterior fossa with a small amount of surrounding vasogenic edema exerting mass effect on the fourth ventricle, with a moderate degree of hydrocephalus.
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Media type:  CT

Media file 2:  Medulloblastoma. Same patient as Image 1. Following intravenous injection of contrast material, the tumor shows marked diffuse and homogeneous enhancement.
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Media type:  CT

Media file 3:  Medulloblastoma in a 27-year-old man. Nonenhanced sagittal T1-weighted image shows a poorly defined, laterally situated, hypointense cerebellar mass with a small cystic area.
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Media type:  MRI

Media file 4:  Medulloblastoma. Axial MRI of the posterior fossa of the same patient as Image 3 shows a right-sided laterally located mass with mixed iso- and hyperintense signal intensity. Surrounding edema is seen as high signal intensity.
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Media type:  MRI

Media file 5:  Medulloblastoma. Coronal T1-weighted postcontrast image in the same patient as Image 3 shows a markedly enhancing peripheral tumor.
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Media type:  MRI

Media file 6:  Medulloblastoma in a 6-year-old boy. Sagittal T1 weighted image shows a slightly hypointense mass in the region of vermis with compression of the fourth ventricle and obstructive hydrocephalus. The brain stem is also compressed by this mass.The lateral and third ventricles are dilated.
	View Full Size Image
Media type:  MRI

Media file 7:  Medulloblastoma. Axial T1 weighted image shows a hypointense mass in the midline, just posterior to the fourth ventricle. The fourth ventricle and brain stem are displaced anteriorly and compressed (same patient as Image 6).
	View Full Size Image
Media type:  MRI

Media file 8:  Medulloblastoma. Axial T2 weighted image reveals a predominantly isointense mass to grey matter with small foci of cystic changes (same patient as Images 6 and 7).
	View Full Size Image
Media type:  MRI

Media file 9:  Medulloblastoma. Axial T1 weighted postcontrast image demonstrates an irregular, heterogenous enhancing mass. Note the dilatation of both temporal horns, indicating obstructive hydrocephalus (same patient as Images 6-8).
	View Full Size Image
Media type:  MRI

REFERENCES

Section 12 of 12

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

• Bloom HJ, Glees J, Bell J, et al. The treatment and long-term prognosis of children with intracranial tumors: a study of 610 cases, 1950-1981. Int J Radiat Oncol Biol Phys. Apr 1990;18(4):723-45. [Medline].
• Dahnert W. Radiology Review Manual. 4th ed. Williams & Wilkins;1999:249-50.
• Kahn D, Follett KA, Bushnell DL, et al. Diagnosis of recurrent brain tumor: value of 201Tl SPECT vs 18F- fluorodeoxyglucose PET. AJR Am J Roentgenol. Dec 1994;163(6):1459-65. [Medline].
• Kun LE. Brain tumors. Challenges and directions. Pediatr Clin North Am. Aug 1997;44(4):907-17. [Medline].
• Lizak P,, Woodruff W. Posterior fossa neoplasms: Multiplanar imaging. Sem.Ultrasound CT MRI. 1992;13:182-206.
• Pizza PA, Poplack DD. Principles and Practice of Pediatric Oncology. 3rd ed. Lippincott-Raven;1997:651-2.
• Ramsey RG. Posterior compartment masses: medulloblastoma. In: Neuroradiology. 2nd ed. W B Saunders Co;1987:557-8.
• Rutka JT. Medulloblastoma. Clin Neurosurg. 1997;44:571-85. [Medline].
• Stark DD, Bradley WG. Medulloblastoma. In: Magnetic Resonance Imaging. 3rd ed. Mosby-Year Book;1999:1474.
• Thapar K, Laws ED. Tumors of the central nervous system. In: Clinical Oncology. Am Cancer Soc;1995:396-7.
• Zee C, Segall HD, Miller C. Less common CT features ofmedulloblastoma. Radiology. 1982;144:97-102.
• Zee CS, Segall HD, Nelson M. Infratentorial Tumors in Children. Neuroimaging Clinics of North Am. 1993;3(4):705-714.
• Zimmerman RA, Bilaniuk LT, Pahlajani H. Spectrum of medulloblastomasdemonstrated by computed tomography. Radiology. 1978;126:137-141.

Article Last Updated: Apr 12, 2007