Primitive Neuroectodermal Tumors of the Central Nervous System

Primitive Neuroectodermal Tumors of the Central Nervous System

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Primitive neuroectodermal tumors (PNET) are neoplasms of which medulloblastoma is the prototype. These are small cell, malignant embryonal tumors showing divergent differentiation of variable degree along neuronal, glial, or rarely mesenchymal lines.

The most recent WHO categorization of embryonal tumors is as follows: [1]

Only tumors of the CNS are discussed here. Peripheral primitive neuroectodermal tumors are regarded as distinct entities. [2]

PNET of the CNS can be divided grossly into infratentorial tumors (medulloblastoma or iPNET) and supratentorial tumors (sPNET).

Considerable controversy exists regarding the histogenesis of these tumors. Initially, these dense, cellular, embryonal tumors were thought to have a common origin from primitive neuroectodermal cells and to differ only in their location, type, and degree of differentiation. In the revised World Health Organization (WHO) classification, however, many of these tumors are given a separate niche on the basis of the assumption that these embryonal tumors also could arise from cells already committed to differentiation. [3]

Regardless of the controversy, these tumors are discussed as infratentorial (medulloblastoma) and supratentorial. The latter occur rarely (25:1) and are more common in young adults than infratentorial tumors.

Spinal dissemination via the cerebrospinal fluid (CSF) is the most common form of metastatic spread of PNETs.

United States

Medulloblastoma represents the most common type of primary solid malignant brain tumor in children (as many as 30% of all solid brain tumors). In contrast, only 1% of brain tumors in adults are medulloblastomas. The overall annual incidence is approximately 0.5 case per 100,000 children. Seventy-five percent arise in the midline (vermis), while 25% occur in the lateral cerebellum.


The Swedish Cancer Registry reported, as part of a population-based study, that medulloblastomas represented 21% of all primary brain tumors in children. Similar figures were provided by the British Tumor Registry and from the United States (Surveillance, Epidemiology and End Results Program).

Risk of sudden death secondary to obstructive hydrocephalus has been hypothesized; however, it is not often observed clinically.

National Cancer Survey suggests a slightly higher incidence in white than in blacks.

A slight male preponderance is observed (male-to-female ratio 1.8:1).

Three fourths of these tumors appear in children younger than 15 years, and 50% are seen in the first decade of life. A second, smaller peak occurs in young adults (aged 21-40 y). [2] Children are 4.6 times as likely to be afflicted by a PNET than adults. [4] Cerebellar medullobastoma occurs rarely in the elderly. [5]

The overall 5 year survival rate is about 53%. [6]

Louis DN, Ohgaki H, Wiestler OD, Cavenee WK, Burger PC, Jouvet A, et al. The 2007 WHO classification of tumours of the central nervous system. Acta Neuropathol. 2007 Aug. 114 (2):97-109. [Medline].

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Kleihues P, Burger PC, Scheithauer BW. The new WHO classification of brain tumours. Brain Pathol. 1993 Jul. 3(3):255-68. [Medline].

Smoll NR, Drummond KJ. The incidence of medulloblastomas and primitive neurectodermal tumours in adults and children. J Clin Neurosci. 2012 Nov. 19 (11):1541-4. [Medline].

Huppmann AR, Orenstein JM, Jones RV. Cerebellar medulloblastoma in the elderly. Ann Diagn Pathol. 2009 Feb. 13(1):55-9. [Medline].

Smoll NR. Relative survival of childhood and adult medulloblastomas and primitive neuroectodermal tumors (PNETs). Cancer. 2012 Mar 1. 118 (5):1313-22. [Medline].

Gulino A, Arcella A, Giangaspero F. Pathological and molecular heterogeneity of medulloblastoma. Current Opinions in Oncology. November 2008. 20(6):668-75.

Guessous F, Li Y, Abounader R. Signalling pathways in Medulloblastoma. Journal of Cell Physiology. December 2008. 217(3):577-583.

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Crawford JR, Rood BR, Rossi CT, Vezina G. Medulloblastoma associated with novel PTCH mutation as primary manifestation of Gorlin syndrome. Neurology. 2009 May 5. 72(18):1618. [Medline].

Allen JC, Donahue B, DaRosso R, Nirenberg A. Hyperfractionated craniospinal radiotherapy and adjuvant chemotherapy for children with newly diagnosed medulloblastoma and other primitive neuroectodermal tumors. Int J Radiat Oncol Biol Phys. 1996 Dec 1. 36(5):1155-61. [Medline].

Ajeawung NF, Wang HY, Kamnasaran D. Progress from clinical trials and emerging non-conventional therapies for the treatment of Medulloblastomas. Cancer Lett. April 2013. 330 (2):130-40. [Medline].

Min HS, Lee JY, Kim SK, Park SH. Genetic grouping of medulloblastomas by representative markers in pathologic diagnosis. Transl Oncol. June 2013. 6 (3):265-72. [Medline].

Albright AL, Pollack IF, Adelson PD. Principles and Practice of Pediatric Neurosurgery. 1st ed. New York: Thieme. 1999: 591-608.

Goldwein JW, Radcliffe J, Johnson J, et al. Updated results of a pilot study of low dose craniospinal irradiation plus chemotherapy for children under five with cerebellar primitive neuroectodermal tumors (medulloblastoma). Int J Radiat Oncol Biol Phys. 1996 Mar 1. 34(4):899-904. [Medline].

Graham DI, Lantos PL. Greenfield’s Neuropathology. 6th ed. New York: Oxford University Press; 1997. Vol 2: 698-710.

Kay A, et al. Brain tumors. First ed. New York: Churchill Livingstone; 1997. 561-574.

Kleihues P, Cavanee WK. Pathology and genetics of tumours of the nervous system. Lyon, France: International Agency for Research on Cancer (IARC); 1997. 49-55.

Kun LE. Brain tumors. Challenges and directions. Pediatr Clin North Am. 1997 Aug. 44(4):907-17. [Medline].

Prados MD, Wara W, Edwards MS, et al. Treatment of high-risk medulloblastoma and other primitive neuroectodermal tumors with reduced dose craniospinal radiation therapy and multi-agent nitrosourea-based chemotherapy. Pediatr Neurosurg. 1996 Oct. 25(4):174-81. [Medline].

Rood BR, Macdonald TJ, Packer RJ. Current treatment of medulloblastoma: recent advances and future challenges. Semin Oncol. 2004 Oct. 31(5):666-75. [Medline].

Russell DS, et al. Pathology of Tumors of the Nervous System. 4th ed. Baltimore: Williams & Wilkins; 1977. 203-26.

Subrata Ghosh, MD, MBBS, MS Staff Physician, Division of Neurosurgery, St. Luke’s Episcopal Hospital, Texas Medical Center, Houston; Assistant Professor of Neurosurgery, Baylor College of Medicine

Subrata Ghosh, MD, MBBS, MS is a member of the following medical societies: American Association of Neurological Surgeons, American Medical Association, Texas Medical Association, Congress of Neurological Surgeons

Disclosure: Nothing to disclose.

Draga Jichici, MD, FRCP, FAHA Associate Clinical Professor, Department of Neurology and Critical Care Medicine, McMaster University School of Medicine, Canada

Draga Jichici, MD, FRCP, FAHA is a member of the following medical societies: American Academy of Neurology, Royal College of Physicians and Surgeons of Canada, Canadian Medical Protective Association, Canadian Medical Protective Association, Neurocritical Care Society, Canadian Critical Care Society, Canadian Critical Care Society, Canadian Neurocritical Care Society, Canadian Neurological Sciences Federation

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Jorge C Kattah, MD Head, Associate Program Director, Professor, Department of Neurology, University of Illinois College of Medicine at Peoria

Jorge C Kattah, MD is a member of the following medical societies: American Academy of Neurology, American Neurological Association, New York Academy of Sciences

Disclosure: Nothing to disclose.

Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS Professor Emeritus of Neurology and Psychiatry, Clinical Professor of Medicine, Clinical Professor of Family Medicine, Clinical Professor of Neurosurgery, State University of New York Upstate Medical University; Neuroscience Director, Department of Neurology, Crouse Irving Memorial Hospital

Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS is a member of the following medical societies: American College of International Physicians, American Heart Association, American Stroke Association, American Academy of Neurology, American Academy of Pain Medicine, American College of Forensic Examiners Institute, National Association of Managed Care Physicians, American College of Physicians, Royal College of Physicians, Royal College of Physicians and Surgeons of Canada, Royal College of Surgeons of England, Royal Society of Medicine

Disclosure: Nothing to disclose.

Roberta J Seidman, MD Associate Professor of Clinical Pathology, Stony Brook University; Director of Neuropathology, Department of Pathology, Stony Brook University Medical Center

Roberta J Seidman, MD is a member of the following medical societies: American Academy of Neurology, Suffolk County Society of Pathologists, New York Association of Neuropathologists (The Neuroplex), American Association of Neuropathologists

Disclosure: Nothing to disclose.

Primitive Neuroectodermal Tumors of the Central Nervous System

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