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Magnetic Resonance Imaging Features of Pilocytic Astrocytoma of the Brain Mimicking High-Grade Gliomas

Kumar, Ashok J. MD; Leeds, Norman E. MD; Kumar, Vinodh A. MD; Fuller, Gregory N. MD, PhD; Lang, Frederick F. MD; Milas, Zvonimir MD; Weinberg, Jeffrey S. MD; Ater, Joann L. MD; Sawaya, Raymond MD

Journal of Computer Assisted Tomography: July 2010 - Volume 34 - Issue 4 - pp 601-611
doi: 10.1097/RCT.0b013e3181d77d52
Neuroradiology

Objective: The typical magnetic resonance/computed tomographic imaging appearance of pilocytic astrocytoma (PA) is that of a cyst with an intensely enhancing mural nodule. The purpose of this study was to illustrate the aggressive imaging features of PA.

Methods: One hundred patients referred to the cancer center with brain tumors histologically proven to be PA were retrospectively reviewed (95 by magnetic resonance imaging and 5 by computed tomographic imaging) and analyzed.

Results: The patient population includes 76 pediatric patients younger than 18 years and 24 adults ranging from 19 to 45 years old. Tumor locations consisted of the following: optic chiasm (22), lateral ventricle (3), thalamus (12), basal ganglia (1), cerebral hemisphere (10), corpus callosum (2), brain stem (26), fourth ventricle (1), and cerebellum (23). The imaging appearance of PA consisted of typical features in 71 cases and aggressive features in 29 cases.

Conclusions: It is important to recognize the aggressive imaging appearance of PA (grade 1 astrocytoma) because it can be mistaken for high-grade gliomas and may thus lead to inappropriate therapy. Despite the aggressive imaging appearance of PA, there is no histopathologic evidence of anaplasia.

From the *Division of Diagnostic Imaging, †Section of Neuropathology, ‡Department of Neurosurgery, and §Department of Pediatric Neuro-Oncology, University of Texas, MD Anderson Cancer Center, Houston, TX.

Received for publication November 10, 2009; accepted February 3, 2010.

Reprints: Ashok J. Kumar, MD, Division of Diagnostic Imaging, MD Anderson Cancer Center, Unit 370, 1515 Holcombe Blvd, Houston, TX 77030 (e-mail: akumar@mdanderson.org).

Advances in knowledge: This article provides new knowledge on the magnetic resonance imaging appearance of pilocytic astrocytoma (PA) with emphasis on aggressive imaging findings described in a large series.

Implications for patient care:

1. The aggressive magnetic resonance imaging appearance of PA has been mistaken for high-grade tumors, such as grade 2 astrocytoma, anaplastic astrocytoma, glioblastoma, ependymoma, and other tumors, such as primitive neuroectodermal tumor and hemangioblastoma.

2. Thus, it is important to entertain the diagnosis of PA in the differential diagnosis of aggressive-appearing tumors in the brain, particularly in the pediatric age group, so that the surgeon and oncologists will be prepared to develop appropriate definitive diagnosis and treatment strategies.

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