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Show EDITORIAL Inflammatory Dural Masses: If It's Not One Thing, It's Another Andrew P. Lieberman, MD, PhD Diffuse or localized dural thickening associated with a dense inflammatory infiltrate presents a challenging differential diagnosis. In the absence of evidence to support other possibilities, the differential quickly narrows to idiopathic hypertrophic pachymeningitis ( IHP), a term used to describe instances in which a chronically inflamed dura is thickened by fibrosis. However, a dense inflammatory infiltrate in the dura may also serve as a veil concealing an underlying neoplasm, such as a lymphoplasmacyte- rich meningioma ( LRM). The difficulties distinguishing between these possibilities are highlighted in two complementary reports in this issue of the Journal ( 1,2). IHP is a clinicopathologic correlation that first requires the exclusion of other causes of a thickened, inflamed dura. Because infections, autoimmune and vasculitic disorders, and malignancies also cause abnormal dural enhancement on imaging studies ( 3), a thorough evaluation is required. Biopsies show a chronic inflammatory infiltrate involving the fibrotic dura ( Fig. 1). The infiltrate typically consists of lymphocytes, plasma cells, and macrophages and does not involve dural blood vessels or the underlying arachnoid or pia. That this inflammatory infiltrate is reactive and not neoplastic is supported by immunohistochemical stains identifying a mixture of B and T lymphocytes and confirming both K and X light chain expression by plasma cells. This appearance on biopsy, coupled with negative tests for microorganisms, most often results in a descriptive pathologic diagnosis also indicating that these findings are consistent with IHP in the appropriate clinical setting. Macrophages are a component of this inflammatory infiltrate, and cases of IHP with noncaseating granulomas have been reported ( 3,4). Others might disagree with the inclusion of granulomatous inflammation in the spectrum of pachymeningitis, instead preferring alternative diagnostic categories such as sarcoidosis. Our current understanding of the pathogenesis of these disorders is incomplete, and consensus criteria for the diagnosis of IHP do not exist. Therefore, we are left to use our discretion in handling such cases, with the comfort of knowing that treatment is similar regardless of the final classification. A pair of studies ( 3,4), which together included a retrospective analysis of cases, documents the most common presentation and course of IHP. The patients were 17 men and 9 women who ranged in age from 37 to 88 years. Headache or cranial neuropathy was the most common presenting symptom, with each affecting - 75% of patients. All showed localized or diffuse dural enhancement on MRI studies. Cerebrospinal fluid lymphocytic pleocytosis was documented in just over half of the patients, and the final classification of the disease process required evaluation by dural biopsy. Worsening clinical symptoms before the initiation of treatment was observed in a minority of patients. A response to antiinflammatory medications was documented in nearly 90% of patients, but benefits were sometimes temporary and partial, and symptoms occasionally recurred as treatment was tapered. Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan. Address correspondence to Andrew P. Lieberman, MD, PhD, 3510 MSRB 1 1150 West Medical Center Drive, Ann Arbor, MI 48109- 0605; E- mail: liebermn( S), umich. edu J Neuro- Ophthalmol, Vol. 27, No. 2, 2007 89 J Neuro- Ophthalmol, Vol. 27, No. 2, 2007 Editorial m* < 4 FIG. 1. Examples of histopathology of idiopathic hypertrophic pachymeningitis. A. Lymphocytes and plasma cells dissecting between collagen bands of fibrotic dura [ hematoxylin and eosin ( H& E) stain]. B. Noncaseating granuloma ( H& E stain). C- D. Immunohisto-chemical stains for the B cell marker CD20 and T cell marker CD3 demonstrate a mixed lymphocytic infiltrate. E- F. Immunohistochemistry demonstrates expression of K and X light chains by plasma cells, supporting a reactive process. kappa In contrast to IHP, the inflammatory infiltrate in LRM is secondary and sometimes obscures the underlying pathology, a World Health Organization grade I meningioma ( 5,6). For unknown reasons, this tumor is associated with a chronic inflammatory infiltrate of plasma cells and lymphocytes. This reactive process is polyclonal and can become quite brisk, mimicking that seen in IHP. Occasionally the inflammatory reaction becomes so vigorous that it includes lymphoid follicles with germinal centers. This tumor may contain a meningiomatous component that is abundant, and in such instances the diagnosis of LRM is less challenging. However, in other cases, the inflammatory component predominates, and reactive meningothelial hyperplasia has to be considered. Of note, LRMs are occasionally associated with hematologic abnormalities, including sinus histiocytosis with mass lymphadenopathy ( 6). This pair of disorders, characterized by the occurrence of idiopathic chronic dural inflammation, offer a series of diagnostic and treatment challenges. They also raise questions about disease pathogenesis. Is the inflammatory response directed against similar antigens in LRM and IHP? Are there shared disease mechanisms with idiopathic inflammatory lesions in other fibrous coverings such as the pericardium? Can we develop our understanding of disease mechanisms to identify new therapeutic targets? For now, these questions remain unanswered as we work to understand this important set of diseases. REFERENCES 1. Hirunwiwatkul P, Trobe JD, Blaivas M. Lymphoplasmacyte- rich meningioma mimicking idiopathic hypertrophic pachymeningitis. J Neuroophthalmol 2007; 27: 91- 94. 2. Hosier MR, Turbin RE, Cho ES, et al. Idiopathic hypertrophic pachymeningitis mimicking lymphoplasmacyte- rich meningioma. J Neuroophthalmol 2007; 27: 95- 98. 3. Kupersmith MJ, Martin Y Heller G, et al. Idiopathic hypertrophic pachymeningitis. Neurology 2004; 62: 686- 94. 4. Riku S, Kato S. Idiopathic hypertrophic pachymeningitis. Neuropa-thology 2003; 23: 335^ 4. 5. Lewis DN, Scheithauer BW, Budka H, et al. Meningiomas. In: Kleihues P Cavenee WK, eds. Pathology and Genetics of Tumors of the Nervous System. Lyon: IARC Press; 2000: 176- 84. 6. Mirra SS, Tindall SC, Check IJ, et al. Inflammatory meningeal masses of unexplained origin: an ultrastructural and immunological study JNeuropathol Exp Neurol 1983; 42: 453- 68. 90 © 2007 Lippincott Williams & Wilkins |
