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Primitive Neuroectodermal Tumors of the Central Nervous System Workup

  • Author: Subrata Ghosh, MD, MBBS, MS; Chief Editor: Tarakad S Ramachandran, MBBS, MBA, MPH, FAAN, FACP, FAHA, FRCP, FRCPC, FRS, LRCP, MRCP, MRCS  more...
 
Updated: Dec 09, 2015
 

Laboratory Studies

Lab tests are not helpful in the diagnosis of primitive neuroectodermal tumors (PNET).

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Imaging Studies

Diagnosis of these clinical entities is confirmed or excluded by lumbar puncture and CT scan and/or MRI. Presence of a mass lesion on an imaging study precludes lumbar puncture because of the risk of herniation.

Clinical diagnosis of these tumors is not possible. Radiologic features unique to each type of tumor may be helpful, but the only possible absolute confirmation is by pathologic examination of the surgical specimen.

MRI

MRI is the imaging technique of choice. The typical tumor is a heterogeneous mass with ill-defined margins arising from the vermis, which fills the fourth ventricle.

Typical findings include moderate to intense enhancement of the tumor, which is not homogenous (see image below).

Cerebellar medulloblastoma. This MRI (axial view, Cerebellar medulloblastoma. This MRI (axial view, T2-weighted image) demonstrates the heterogeneity of the tumor.

Accompanying hydrocephalus is common (see image below), and associated cystic changes can occur (see image below).

Cerebellar medulloblastoma. This sagittal view MRI Cerebellar medulloblastoma. This sagittal view MRI without contrast demonstrates characteristic midline cerebellar location with mild obstructive hydrocephalus.

The entire neuraxis should be imaged to detect spinal metastases, which may occur via subarachnoid dissemination.

CT scan

In emergent situations, CT scan is preferred over MRI because of its easy accessibility. However, CT scan resolution is inferior to that of MRI. The mass is typically midline, relatively heterogeneous, and variably contrast enhancing. (See the image below.)

Cerebellar medulloblastoma. This axial view CT sca Cerebellar medulloblastoma. This axial view CT scan with contrast shows a partially enhancing mass arising in the midline from cerebellum and filling the fourth ventricle.

CT myelogram may be used to rule out spinal dissemination in cases in which MRI is contraindicated.

MR spectroscopy

As compared to the normal cerebellum, these tumors on MR spectroscopy reveal a heterogeneous picture with decreased N- acetyl-aspartate (NAA) and creatine peaks and increased choline peaks.

The technique is still considered experimental.

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Procedures

See the list below:

  • Ventriculostomy is rarely done preoperatively because of the risk of upward herniation.
  • Preoperative lumbar puncture is avoided because of the risk of downward herniation.
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Histologic Findings

See the list below:

  • Primitive cells are observed growing in sheets or cords of dense cellularity with increased mitotic index and increased nuclear-cytoplasmic ratio.
  • Formation of Homer-Wright rosettes (ie, neuroblastic rosettes consisting of tumor cell nuclei disposed in a circular fashion about tangled cytoplasmic processes) is typical but not always seen and is not essential for diagnosis. When present, it is frequently associated with marked nuclear pleomorphism and high mitotic activity.
  • Associated gross pathologic findings may include cystic changes, although the tumors are usually solid. They may vary from soft to firm in consistency. Geographic areas of necrosis, vascular proliferation, or calcification are less common, while hemorrhage is rare.
  • Immunohistochemical markers can confirm differentiation toward astrocytic or neuronal lineage.
  • Unusual variants include those with melanin deposition, rhabdomyoblastic differentiation, or desmoplastic features, among others.
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Contributor Information and Disclosures
Author

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.

Coauthor(s)

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.

Specialty Editor Board

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.

Chief Editor

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.

Additional Contributors

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.

References
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Cerebellar medulloblastoma. This MRI (axial view, T2-weighted image) demonstrates the heterogeneity of the tumor.
Cerebellar medulloblastoma. This sagittal view MRI without contrast demonstrates characteristic midline cerebellar location with mild obstructive hydrocephalus.
Cerebellar medulloblastoma. This axial view CT scan with contrast shows a partially enhancing mass arising in the midline from cerebellum and filling the fourth ventricle.
 
 
 
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