DOI: 10.1148/rg.254045207
RadioGraphics 2005;25:1075-1080
© RSNA, 2005
Best Cases from the AFIP
Idiopathic Tumefactive Hypertrophic Pachymeningitis1
Imran A. Kazem, MD,
Natasha L. Robinette, MD,
Norbert Roosen, MD,
Michael F. Schaldenbrand, MD and
Joon K. Kim, MD
1 From the Department of Radiology, Oakwood Healthcare System, 18101 Oakwood Blvd, Dearborn, MI 48124. Received December 1, 2004; revision requested January 10, 2005 and received February 21; accepted February 25. All authors have no financial relationships to disclose.
Address correspondence to I.A.K. (e-mail: doctorkazem{at}yahoo.com).
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History
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A 42-year-old man presented with complaints of chronic daily right frontal headaches for the past 9 months. His headaches were worse in the morning and throbbing in nature. The headaches had increased in intensity, with minimal relief of symptoms provided by acetaminophen or ibuprofen. Decreased visual acuity in the right eye, loss of balance over the past 6 months, and an unintentional weight loss of 50 pounds over the past year were also noted. Results of neurologic examination confirmed decreased visual acuity in the right eye but were otherwise essentially unremarkable. Results of a complete blood work-up and comprehensive metabolic testing were normal. In addition, rheumatologic, oncologic, and infectious disease work-ups were negative. The patient’s past medical history was noncontributory, and family history was significant only for scleroderma in the patient’s mother. Magnetic resonance (MR) imaging of the brain revealed a large right frontal lobe mass, which was thought to represent a meningioma and possible en plaque meningioma or coexisting meningeal disease. The patient underwent cerebral angiography followed by surgical resection of the mass.
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Imaging Findings
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MR imaging of the brain (1.5T GE Signa Excite; GE Healthcare, Waukesha, Wis) demonstrated a lobulated right frontal lobe mass measuring 7.0 x 4.1 x 5.0 cm in the anteroposterior, transverse, and craniocaudal dimensions, respectively. The mass was thought to be extraaxial in location, abutting the dura mater. An adjacent 1.0 x 1.0 x 1.0-cm satellite mass with similar features was identified more laterally in the right frontal lobe (Fig 1). There was significant mass effect compressing the right lateral ventricle and the frontal horn of the left lateral ventricle, as well as midline shift to the left (Fig 2a). The white matter demonstrated surrounding vasogenic edema and transependymal cerebral spinal fluid flow along the left occipital horn from compression of the foramen of Monroe (Fig 2b, 2c).
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Figure 1. Coronal gadolinium-enhanced T1-weighted MR image reveals a large, lobulated right frontal lobe mass with an adjacent satellite lesion (arrow). Dural thickening and enhancement are seen along the frontal lobes and anterior falx (arrowheads).
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Figure 2a. (a) Axial T1-weighted MR image shows the mass (*) to be isointense relative to gray matter. There is midline shift to the left (arrow), with mass effect on the right lateral ventricle and the frontal horn of the left lateral ventricle (arrowheads). (b) On an axial T2-weighted MR image, the mass is again isointense relative to gray matter and contains scattered hyperintense foci. (c) Axial fluid-attenuated inversion recovery MR image demonstrates vasogenic white matter edema (arrows). Transependymal cerebral spinal fluid flow is seen adjacent to the occipital horn of the left lateral ventricle (arrowhead).
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Figure 2b. (a) Axial T1-weighted MR image shows the mass (*) to be isointense relative to gray matter. There is midline shift to the left (arrow), with mass effect on the right lateral ventricle and the frontal horn of the left lateral ventricle (arrowheads). (b) On an axial T2-weighted MR image, the mass is again isointense relative to gray matter and contains scattered hyperintense foci. (c) Axial fluid-attenuated inversion recovery MR image demonstrates vasogenic white matter edema (arrows). Transependymal cerebral spinal fluid flow is seen adjacent to the occipital horn of the left lateral ventricle (arrowhead).
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Figure 2c. (a) Axial T1-weighted MR image shows the mass (*) to be isointense relative to gray matter. There is midline shift to the left (arrow), with mass effect on the right lateral ventricle and the frontal horn of the left lateral ventricle (arrowheads). (b) On an axial T2-weighted MR image, the mass is again isointense relative to gray matter and contains scattered hyperintense foci. (c) Axial fluid-attenuated inversion recovery MR image demonstrates vasogenic white matter edema (arrows). Transependymal cerebral spinal fluid flow is seen adjacent to the occipital horn of the left lateral ventricle (arrowhead).
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At T1- and T2-weighted MR imaging, the mass was isointense relative to gray matter (Fig 2a, 2b). T2-weighted imaging also demonstrated scattered hyperintense foci within the mass (Fig 2b). After intravenous administration of gadolinium-based contrast material, the mass demonstrated homogeneous enhancement as well as intermittent areas of focally thickened dura mater with intense enhancement, including the right optic foramen and the cavernous sinuses (Fig 3a). There was no "dural tail" enhancement adjacent to the mass. Intermittent areas of dural and leptomeningeal thickening and enhancement were seen predominantly along the frontal lobes, the anterior falx, and the anterior aspect of the temporal lobes (Fig 3). No bone erosion or hyperostosis in the underlying calvaria was evident at MR imaging. Cerebral angiography demonstrated an avascular lesion with mass effect and no evidence of tumor blush to suggest meningioma.
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Figure 3a. (a) Axial gadolinium-enhanced T1-weighted MR image reveals thickening and enhancement of the dura mater along the anterior and medial aspects of the temporal lobes (arrows). (b) Axial gadolinium-enhanced T1-weighted MR image shows enhancement of the mass and thickening of the dura mater in the frontal lobes, left temporal lobe, and falx (arrows). Leptomeningeal enhancement is noted in the medial left frontal lobe sulci (arrowhead).
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Figure 3b. (a) Axial gadolinium-enhanced T1-weighted MR image reveals thickening and enhancement of the dura mater along the anterior and medial aspects of the temporal lobes (arrows). (b) Axial gadolinium-enhanced T1-weighted MR image shows enhancement of the mass and thickening of the dura mater in the frontal lobes, left temporal lobe, and falx (arrows). Leptomeningeal enhancement is noted in the medial left frontal lobe sulci (arrowhead).
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Pathologic Evaluation
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At surgical resection, the extraaxial mass was removed in two separate sections, the external surfaces of which appeared lobular and pink-yellow. The cut surface was also pink-yellow and demonstrated minimal glistening (Fig 4). Histologic findings in the mass were consistent with marked fibrotic thickening of the dura mater. Numerous entrapped necrotizing and nonnecrotizing granulomas interspersed with multiple macrophages were seen throughout the thickened dura mater (Fig 5). Periodic acid–Schiff and acid-fast bacilli (AFB) stains, as well as cultures for aerobes, anaerobes, fungus, and AFB, were all negative. Histopathologic findings were compatible with idiopathic hypertrophic pachymeningitis (IHP).
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Figure 5a. (a) Low-power photomicrograph (original magnification, x 40; hematoxylineosin stain) of the resected dural mass shows necrotizing (arrows) and nonnecrotizing (arrowheads) granulomas. (b) Higher-power photomicrograph (original magnification, x 100; hematoxylineosin stain) shows a necrotizing granuloma. Central caseous tissue necrosis is surrounded by fibrosis and numerous macrophages (dark blue).
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Figure 5b. (a) Low-power photomicrograph (original magnification, x 40; hematoxylineosin stain) of the resected dural mass shows necrotizing (arrows) and nonnecrotizing (arrowheads) granulomas. (b) Higher-power photomicrograph (original magnification, x 100; hematoxylineosin stain) shows a necrotizing granuloma. Central caseous tissue necrosis is surrounded by fibrosis and numerous macrophages (dark blue).
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Discussion
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Hypertrophic pachymeningitis is a clinical disorder characterized by localized or diffuse enlargement of the dura mater (1–6). The underlying and neighboring leptomeninges (pia mater, arachnoidea mater) become opaque and thickened as well. These changes in the meninges can be identified in a variety of neoplastic, autoimmune, and infectious disease processes (Table) (2,7,8). If an exhaustive work-up fails to identify the cause of the meningeal changes, a diagnosis of IHP is made.
IHP is a rare disorder affecting men more often than women (2,9), with peak prevalence occurring in the 6th decade of life (5,9). Chronic headaches, often resembling chronic migraines with or without other neurologic manifestations, are the most common presenting symptom of IHP (2,3,5,7,10–12). Other neurologic symptoms of IHP include cranial nerve palsies (cranial nerves IV–VIII), cerebellar ataxia, seizures, and neuroophthalmic symptoms such as visual field loss, complete blindness, optic neuropathy, and increased intracranial pressure with papilledema (2,3,5,7,10–12). The neurologic manifestations are attributed to compression of cranial nerves at the skull base by enlarged dura mater resulting from the chronic inflammatory process. The ensuing headache may be due to focal meningeal irritation or, possibly, to localized arachnoiditis (3). Further documented neurologic complications of IHP include venous sinus thrombosis (4,6,11), obstructive hydrocephalus (6), and cerebral edema (2). The literature suggests an association of IHP with many interesting syndromes including Tolosa-Hunt syndrome (granulomatous inflammation of the wall of the cavernous sinus resulting in painful ophthalmoplegia) (2,5,6,12,13), cranial polyneuritis (especially with involvement of the 7th–12th cranial nerves) (2,6), multifocal fibrosclerosis (chronic granulomatous inflammation consisting of retroperitoneal fibrosis, Riedel thyroiditis, sclerosing cholangitis, and pseudotumor oculi) (2,4,6), and diabetes insipidus (6,11–13).
Neuroimaging is essential in making the correct preoperative diagnosis of IHP in patients with chronic headaches. Contrast material–enhanced computed tomography (CT) reveals diffuse thickening and enhancement of the dura mater (3,8). It is well known that gadolinium-enhanced MR imaging is superior to contrast-enhanced CT in the evaluation of leptomeningeal disease, including IHP. Findings of infiltrating meningeal lesions (including IHP) can be subtle at unenhanced MR imaging, and lack of contrast-enhanced imaging is the primary cause of delayed diagnosis (3). MR imaging should include T1-weighted, T2-weighted, and gadolinium-enhanced T1-weighted sequences in multiple projections. Typically, IHP demonstrates smooth or nodular dural thickening that is isointense or hypointense with both T1- and T2-weighted sequences. It also shows avid enhancement after intravenous administration of contrast material. These signal intensity characteristics are due to the fibrosis and necrosis of the dura mater (4,5,10,11). Peripheral hyperintensity can be seen on T2-weighted images and is thought to represent active inflammation or increased vascularity of the dura mater and underlying parenchyma. However, in the present case, MR imaging findings were somewhat atypical for IHP, with tumefactive enlargement of the dura mater mimicking a meningioma. However, even though IHP can manifest as a dural mass mimicking a meningioma (8,14), there are few documented cases in the literature. Angiography typically reveals an avascular mass (14).
Because of (a) the small number of cases in which IHP has been identified early in the course of the disease and (b) the overall rarity of IHP, the natural history and prognosis of this disease entity are not well documented. The current standard of treatment is intended to curb the inflammatory response that causes much of the morbidity associated with the disease. Although there have been few verified clinical trials, the administration of systemic corticosteroids and immunomodulating agents such as azathioprine and cyclophosphamide has been somewhat successful in the treatment of IHP (2,3,10,12,13). A recent study documented the successful use of intraventricular cytarabine in a patient who did not respond to steroids or immunomodulating agents (15). The clinical outcome varies, ranging from complete resolution of symptoms to progressive worsening of the disease leading to steroid dependence or the need for surgical debulking. Follow-up MR imaging to assess treatment efficacy is somewhat controversial because clinical improvement and imaging findings often do not correlate (3,9,10,13).
The patient in this case experienced significant improvement of symptoms after undergoing surgical resection of the right frontal dural mass. After undergoing surgery, the patient was placed on a tapering oral steroid regimen and remained asymptomatic for several months. Shortly after the steroid regimen had ended, the patient reported recurrence of occasional right-sided headaches and right ophthalmalgia. Follow-up MR imaging performed 2 months after surgery revealed postsurgical changes in the right frontal lobe, resolution of midline shift, and linear dural enhancement in the anterior frontal lobes and anterior falx (Fig 6). MR imaging performed 8 months after surgery demonstrated stable dural enhancement in the frontal lobes and falx. However, recurrent nodular dural enhancement was seen in the left temporal lobe at the level of the Sylvian cistern, a finding that is consistent with recurrent pachymeningitis (Fig 7).
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Figure 6. Axial gadolinium-enhanced T1-weighted MR image obtained 2 months after resection shows linear dural enhancement along the frontal lobes and anterior falx (arrows). Postsurgical changes are seen in the right frontal lobe (*).
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Summary
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Hypertrophic pachymeningitis is an extremely rare fibrosing inflammatory process involving the dura mater and, often, the tentorium. Numerous pathologic entities can produce thickening of the pachymeninges; thus, idiopathic pachymeningitis is a diagnosis of exclusion. Typically, IHP demonstrates linear or nodular dural thickening with intense contrast enhancement at MR imaging. The present case is extremely unusual, with IHP manifesting as a large enhancing mass mimicking a meningioma with intermittent dural thickening.
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Acknowledgments
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The authors gratefully thank infectious disease specialist Raphael J. Kiel, MD, and neurosurgical physician assistant Taibi Chbihi, PA-C, for their invaluable contributions.
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Footnotes
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Abbreviations: IHP = idiopathic hypertrophic pachymeningitis
Editor’s Note.—Everyone who has taken the course in radiologic pathology at the Armed Forces Institute of Pathology (AFIP) remembers bringing beautifully illustrated cases for accession to the Institute. In recent years, the staff of the Department of Radiologic Pathology has judged the "best cases" by organ system, and recognition is given to the winners on the last day of the class. With each issue of RadioGraphics, one or more of these cases are published, written by the winning resident. Radiologic-pathologic correlation is emphasized, and the causes of the imaging signs of various diseases are illustrated.
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References
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History
Imaging Findings
