AFIP ARCHIVES 1693 From the Archives of the AFIP Pilocytic Astrocytoma: Radiologic- Pathologic Correlation1 Kelly K. Koeller, CAPT, MC, USN ● Elisabeth J. Rushing, CME FEATURE RadioGraphics COL, MC, USA See accompanying test at http:// www.rsna.org /education Pilocytic astrocytoma is the most common pediatric central nervous /rg_cme.html system glial neoplasm and the most common pediatric cerebellar tu- mor. This tumor has a noteworthy benign biologic behavior that trans- LEARNING OBJECTIVES lates into an extremely high survival rate—94% at 10 years—that is by FOR TEST 6 far the best of any glial tumor. Most patients present in the first 2 de- After reading this cades, and clinical symptoms and signs are usually of several months article and taking the test, the reader duration and directly related to the specific location of the tumor. The will be able to: cerebellum, optic nerve and chiasm, and hypothalamic region are the Ⅲ Describe the salient most common locations, but the tumor can also be found in the cere- demographic and clinical features of bral hemisphere, ventricles, and spinal cord. Surgical resection is the pilocytic astrocy- treatment of choice for all tumors, except for those involving the optic toma. pathway and hypothalamic region, which may be treated with radiation Ⅲ Identify the charac- teristic imaging ap- therapy and chemotherapy. Cross-sectional imaging often demon- pearances of pilocytic strates a classic appearance: a cystic mass with an enhancing mural astrocytoma in chil- dren and adults, in- nodule. Less common appearances are quite nonspecific. Surrounding cluding the presence vasogenic edema is rarely present, and this feature provides a valuable of dissemination. Ⅲ Discuss the direct clue to the correct diagnosis. Accurate interpretation of imaging stud- correlation of the ies plays an essential role in directing treatment of these tumors, par- imaging appearances ticularly when they arise in the optic pathway of patients with neurofi- with the gross patho- logic and histologic bromatosis type 1. Disseminated disease and recurrence are extremely appearances in pilo- rare. cytic astrocytoma. Abbreviations: NF1 ϭ neurofibromatosis type 1, WHO ϭ World Health Organization Index terms: Astrocytoma, 10.3639 ● Brain neoplasms, 10.3639 ● Neoplasms, in infants and children, 10.3639 RadioGraphics 2004; 24:1693–1708 ● Published online 10.1148/rg.246045146 ● Content Codes: 1From 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, Rm M-121, Washington, DC 20306-6000; Department of Radiology and Radiological Sciences, 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 19, 2004; revision requested August 20 and received September 7; accepted September 7. Both authors have no financial relationships to disclose. Address cor- respondence to K.K.K. (e-mail: koeller@afip.osd.mil). The opinions and assertions contained herein are the private views of the authors and are not to be construed as official nor as representing the views of the Departments of the Navy, Army, or Defense. 1694 November-December 2004 RG f Volume 24 ● Number 6 Introduction Most of the lesions occur in or near the midline, Originally identified in a series of 76 cases of cer- usually arising from the cerebellum, the optic ebellar astrocytomas by Harvey Cushing in 1931, nerve and chiasm, or the region of the hypothala- the pilocytic astrocytoma occupies a unique place mus-thalamus. Less common locations include among cerebral neoplasms (1). With its notable the cerebral hemispheres, the cerebral ventricles, indolent biologic behavior, pilocytic astrocytoma velum interpositum, and spinal cord (5–9). In carries one of the highest survival rates of any adults, the tumor more frequently occurs in the brain tumor and certainly the highest rate for any cerebral hemisphere (8,10). astrocytoma. Yet, as reviewed herein, there are The association of pilocytic astrocytoma with numerous oddities about this neoplasm. It appears neurofibromatosis type 1 (NF1) is well docu- well circumscribed, yet occasionally it infiltrates mented. Pilocytic astrocytoma is the most com- the surrounding brain tissue, as seen at histologic mon tumor seen in this population, occurring in RadioGraphics examination. It enhances intensely, sometimes up to 15%–21% of all NF1 patients, and typically with a ringlike pattern that is more commonly involves the optic nerve or chiasm (3,11–16). Be- seen in highly malignant astrocytomas, yet it is cause the vast majority of optic pathway gliomas not a high-grade neoplasm. In rare cases, it can are histologically regarded as pilocytic astrocy- even produce widespread dissemination, which toma, it has been suggested that the most appro- seems incongruous for a brain tumor with slow priate term for this entity should be “pilocytic growth and fairly bland histologic characteristics. astrocytoma of the optic pathway” (16). Nearly Even more fascinating, such metastatic spread all optic pathway gliomas in NF1 patients mani- can occur without associated increased mortality, fest before the age of 6 years and females are more in contrast to the poor prognosis so common in commonly affected by a 2:1 ratio (16,17). Of all patients with metastatic high-grade tumors. In patients with an optic pathway glioma, about one- view of these many contradictions, pilocytic astro- third have NF1, and, of all tumors in this region, cytoma qualifies as “the tumor that is the excep- 40%–70% occur in NF1 patients (14,16,18). tion to the rule.” Pilocytic astrocytomas account for 1.5%–3.5% In this article, we use case material from the of all orbital neoplasms and two-thirds of all neo- Thompson Archives of the Department of Radio- plasms of the optic nerve (3). Most optic pathway logic Pathology at the Armed Forces Institute of pilocytic astrocytomas (75%) arise in children less Pathology to illustrate the spectrum of cross-sec- than 12 years old; in addition, the tumor is more tional imaging manifestations of this common likely to arise in the optic nerve in children, tumor and to present a comprehensive summa- whereas it is more commonly located in the optic tion of the history, pertinent clinical findings, chiasm in adolescents and young adults (19,20). pathologic features, histogenesis, and prognosis Involvement of the chiasm and hypothalamus has associated with this tumor. Salient demographic been reported to occur in 25%–60% of patients and imaging features of pilocytic astrocytoma are (11,19,20). Optic pathway gliomas much less listed in the Table. commonly manifest in adult patients without NF1; when they do, these tumors have a dramati- Epidemiologic Characteristics cally different biologic behavior and are regarded Pilocytic astrocytoma is the most common pediat- histologically as anaplastic astrocytoma or glio- ric cerebellar neoplasm and the most common blastoma multiforme (21). pediatric glioma, constituting 85% of all cerebel- lar astrocytomas and 10% of all cerebral astrocy- Clinical Features tomas in this age group (2). Overall, it accounts Clinical presentation of patients with a pilocytic for 0.6%–5.1% of all intracranial neoplasms and astrocytoma varies with its site of origin. Head- 1.7%–7% of all glial tumors (3). ache, vomiting, gait disturbance, blurred vision, Pilocytic astrocytoma occurs most commonly diplopia, and neck pain are common symptoms in in children and young adults, with most cases patients with a cerebellar pilocytic astrocytoma (75%) manifesting in the first 2 decades of life (22–24). Clinical signs usually include hydro- (2,4). No gender predilection is reported (2). cephalus, papilledema, truncal ataxia, appendicu- lar dysmetria, head tilt, sixth nerve palsy, and nys- tagmus (22,24). RG f Volume 24 ● Number 6 Koeller and Rushing 1695 Characteristics of Pilocytic Astrocytoma Feature Characteristic Manifestation Prevalence Most common (85%) pediatric cerebellar neoplasm and most common pediatric glioma; constitutes 10% of all childhood intracranial neoplasms, 0.6%–5% of all in- tracranial tumors, and 1.7%–7% of all gliomas Age Most patients present before 20 years of age; about 25% are older than 18 years at time of presentation Gender No predominance Location Cerebellum, brainstem, optic nerve and optic chiasm, hypothalamus/thalamus most common; cerebral hemisphere, ventricles, and spinal cord less common; in adults, more common in cerebral hemisphere RadioGraphics Clinical symptoms Dependent on location; typically long duration; tumors in the cerebellum manifest with and signs headache, vomiting, gait disturbance, blurred vision, papilledema, truncal ataxia Special features Association with neurofibromatosis type 1, especially for tumors located in the optic pathway Histologic features Reactive astrocytes with biphasic morphology (loose glial component and compact pi- loid regions), eosinophilic granular bodies (“protein droplets”), Rosenthal fibers; pi- lomyxoid subtype has affinity for hypothalamic region CT appearance Hypoattenuated cystlike component combined with isoattenuated soft-tissue mural nodule MR imaging ap- On T1-weighted images, intense to hypointense; on T2-weighted images, hyperintense pearance (cystic portion), mixed signal (soft-tissue portion); mural nodule shows intense en- hancement; other patterns: ringlike enhancement of cysts, solid near homogeneous enhancement, necrosis with central nonenhancing