Arch Pathol Lab Med—Vol 133, January 2009 Intracranial Lesions Mimicking Neoplasms—Cunliffe et al 101 Review Article Intracranial Lesions Mimicking Neoplasms Clare H. Cunliffe, MD; Ingeborg Fischer, MD; David Monoky, MD; Meng Law, MD, MBBS, FRACR; Carolyn Revercomb, MD; Susan Elrich, MD; Michael Jered Kopp, BA; David Zagzag, MD, PhD ● Context.—A broad spectrum of nonneoplastic conditions can mimic a brain tumor, both clinically and radiologically. In this review we consider these, taking into consideration the following etiologic categories: infection, demyelin- ation, vascular diseases, noninfectious inflammatory dis- orders, and iatrogenic conditions. We give an overview of such diseases, which represent a potential pitfall for pa- thologists and other clinicians involved in patient care, and present selected cases from each category. Objective.—To illustrate the radiologic and pathologic features of nontumoral intracranial lesions that can clini- cally and radiologically mimic neoplasia. Data Sources.—Case-derived material and literature re- view. Conclusions.—A variety of nonneoplastic lesions can present clinically and radiologically as primary or meta- static central nervous system tumors and result in surgical biopsy or resection of the lesion. In such situations, the pathologist has an important role to play in correctly de- termining the nature of these lesions. Awareness of the en- tities that can present in this way will assist the pathologist in the correct diagnosis of these lesions. (Arch Pathol Lab Med. 2009;133:101–123) A broad spectrum of nonneoplastic conditions can radio- logically and clinically mimic an intracranial neo- plasm. In this review, we have compiled a unique series of cas- es that presented both clinically and radiologically as in- tracranial mass lesions. Tumor was initially considered in each of the cases. However, pathology revealed a variety of nonneoplastic etiologies, including demyelinating dis- ease, vascular disease, inflammation, and infection, as well as posttreatment effects. Although tumor is often the most likely diagnostic consideration in a patient presenting with a contrast-enhancing mass lesion within the brain paren- chyma with surrounding edema and mass effect, that is not always the case. Not uncommonly, there can be sig- nificant overlap in the radiologic presentation between neoplastic and nonneoplastic diseases. Both neoplastic and nonneoplastic diseases can produce abnormal contrast en- hancement, mass effect, and perilesional edema on both computed tomography (CT) and magnetic resonance im- aging (MRI). Occasionally, some of these nonneoplastic etiologies may produce signs and symptoms mimicking tumoral disease clinically. 1 As such, these situations may Accepted for publication July 25, 2008. From the Department of Pathology, Division of Neuropathology (Drs Cunliffe, Fischer, and Zagzag) and Department of Radiology, Division of Neuroradiology (Dr Monoky), NewYork University Medical Center, New York; the Departments of Radiology and Neurosurgery, Mount Sinai Medical Center, NewYork, NY (Dr Law); the Office of the Chief Medical Examiner, Washington, DC (Dr Revercomb); the Department of Neurology,Yale University Hospital, New Haven, Conn (Dr Elrich); and the Stern School of Business, New York University, NewYork (Mr Kopp). The authors have no relevant financial interest in the products or companies described in this article. Reprints: Clare H. Cunliffe, MD, Department of Pathology, Division of Neuropathology, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029 (e-mail: clare@drcunliffe.com). offer a diagnostic challenge to both the clinician and ra- diologist, and often these patients undergo biopsy. In most cases, the pathologist can readily differentiate between neoplasia and nonneoplastic imitators. However, because the benign nature of some pseudoneoplastic lesions may not be immediately apparent on pathologic examination, it behooves the pathologist to be aware of their existence. The purpose of this case series is to alert pathologists, radiologists, and other clinicians involved in the care of neurooncologic patients to consider nonneoplastic etiolo- gies in the differential diagnosis of both intra-axial and extra-axial mass lesions. Tumor-mimicking conditions from several etiologic cat- egories are presented in tabular form, including infection and inflammation, demyelinating disease, vascular dis- ease, and posttreatment conditions, with accompanying il- lustrations and discussion of the current and pertinent lit- erature. Case examples of each condition discussed are described in the Table. INFECTIONS Case Example 1: Aspergilloma The radiologic finding of erosion of the skull base by this mass lesion may have contributed to its interpretation as a destructive neoplasm, with the differential diagnosis including chondrosarcoma, metastatic lesion, osteosarco- ma, and meningioma. However, the histology in this case ruled out a diagnosis of neoplasm. Based on the hematoxylin-eosin morphology of a granulomatous process, a diagnosis of tuberculosis came to mind. Special stains for microorganisms solved this differential diagnostic dilemma, highlighting fungal hyphae with the characteristic acute angle branching of Aspergillus species. In retrospect, the history of otitis me- dia and mastoidectomy in this patient pointed toward an infectious process, even in the absence of predisposing factors such as immunosuppression or diabetes. Even