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Table of Contents
Year : 2021  |  Volume : 4  |  Issue : 1  |  Page : 16-21

Primary meningeal inflammatory pseudotumor

1 Neurosurgical Oncology Services, Department of Surgical Oncology, Tata Memorial Centre, Mumbai, India
2 Department of Pathology, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, India

Date of Submission13-Oct-2020
Date of Acceptance20-May-2021
Date of Web Publication12-Apr-2022

Correspondence Address:
Prof. Aliasgar V Moiyadi
Neurosurgical Oncology Services, Department of Surgical Oncology, Tata Memorial Centre, Mumbai 400012, Maharashtra.
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/IJNO.IJNO_22_20

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Inflammatory pseudotumors (IPs) encompass a wide spectrum of pathological entities of varying nomenclatures such as plasma cell granuloma, xanthomatous pseudotumor, and hypertrophic pachymeningitis. Majority of them are of uncertain etiology. Such tumor-mimicking lesions have been described in the lungs, liver, peritoneum, and retroperitoneal spaces. Primary convexity meningeal occurrence without intracerebral extension or extracranial presence is uncommon. We present one such rare case of a 50-year-old woman having a convexity primary meningeal IP with a 4-year follow-up post-excision.Radiology of IP may be nonspecific and pathological diagnosis is necessary in most cases to rule out meningeal neoplasms or infections, autoimmune/vasculitic, and other unusual mimics. Although surgical excision is warranted, complete resection may not be necessary if the frozen report is diagnostic. The differential diagnosis and treatment options are discussed further and a flowchart is provided depicting the meningeal tumor mimics.

Keywords: Inflammatory pseudotumor, meningeal tumor, meningioma, plasma cell granuloma

How to cite this article:
Shaikh ST, Sridhar E, Moiyadi AV. Primary meningeal inflammatory pseudotumor. Int J Neurooncol 2021;4:16-21

How to cite this URL:
Shaikh ST, Sridhar E, Moiyadi AV. Primary meningeal inflammatory pseudotumor. Int J Neurooncol [serial online] 2021 [cited 2022 Jun 27];4:16-21. Available from: https://www.Internationaljneurooncology.com/text.asp?2021/4/1/16/342819

  Introduction Top

Non-neoplastic tumor-mimicking lesions go by a variety of synonyms viz. inflammatory pseudotumor (IP), plasma cell granuloma, post-inflammatory tumor, and xanthomatous pseudotumor.[1] There have been so far around 100 cases of central nervous system (CNS) involvement published in the literature with approximately 60 of them showing meningeal involvement.[2] We report one such unusual meningeal pseudotumor and review the diagnostic dilemmas and management options.

  Case description Top

A 50-year-old woman presented with complaints of recurrent generalized seizures since 2 years. Her differential blood counts were normal. Magnetic resonance imaging (MRI) was suggestive of a well-defined, lobulated right frontoparietal extraaxial lesion, which was hypointense on T1-weighted (W), isointense on T2W/FLAIR [Figure 1]A, and homogenously enhancing on post-contrast scans. There was an unusually long dural tail and diffuse white matter edema around it [Figure 1]B. Diffusion restriction was absent. Blooming on T2W scans at the periphery of lesion was thought to represent calcifications. Both fluorodeoxyglucose-positron emission tomography (FDG-PET) and gallium-68 (Ga68)-DOTANOC positron emission tomography-computed tomography (PET-CT) showed uptake corresponding to increased somatostatin and GLUT expression raising the possibility of atypical meningioma and hemangiopericytoma.
Figure 1: (A) T2W MRI image showing a well-defined isointense lobulated extraaxial lesion in the right frontoparietal region. (B) Post-contrast MRI showing homogenous enhancement with an unusually long dural tail and surrounding diffuse white matter edema

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Intraoperatively, the dura was bulging, congested, and was incised circumferentially. There was an interdural (thickened fusiform dura) component along with another lobulated intradural firm gritty part burrowing into and invading the pia. Pia was coagulated and the entire tumor was dissected off with the attached dura en bloc [Figure 2].
Figure 2: Intradural firm gritty tumor with the attached dura

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Pathology showed sheets of plasma cells admixed with small lymphoid cells [Figure 3] and scattered foci of neutrophilic microabscess. Adjoining adherent rim of brain parenchyma showed perivascular lymphocytic infiltrate with reactive gliotic changes, without eosinophils. Patchy pale areas of hyalinization were noted but no definite areas of dense fibrosis or storiform architecture were identified. No meningeal cell proliferation or meningeal whorls were seen. Special stains did not reveal fungi or other organism. On immunohistochemistry (IHC) [Figure 4], CD138 marked the sheets of plasma cells, which showed admixture of both kappa and lambda positive cells (negative for light chain restriction). IgG4/IgG ratio was insignificant. CD20 and CD3 revealed a marked admixture of B and T-lymphocytes. ALK-1, CD56, and cyclin D1 were negative. The systemic evaluation did not reveal any features of multiple myeloma. Clonality analysis by multiplex polymerase chain reaction (PCR) was negative for B-cell gene rearrangement. Given these findings together with a mass-like lesion, a possibility of inflammatory plasma cell-rich lesion along the spectrum of IPs was considered.
Figure 3: Representative photomicrographs (hematoxylin and eosin stain––Ax100; Bx200; Cx400 and Dx400) showing lesion composed of sheets of cells of lymphoplasmacytoid morphology (black arrow) with no admixture of other inflammatory cells

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Figure 4: Representative IHC images (A–H) (x200). (A) Lesional cells positive for CD138 (black arrow). (B) Lesional cells positive for MUM1 (black arrow). (C) CD20 positive small B-lymphoid cells (black arrow). (D) Absent germinal centers and sparse infiltrate of CD3 positive T-lymphoid cells (black arrow). (E) Lesional cells positive for IgG (black arrow). (F) No significant population of IgG4 positive cells. (G) Plasma cells showing admixture of kappa cells (black arrow). (H) Lambda light chain positive cells (black arrow) with no evidence of restriction

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The patient recovered uneventfully and was started on a short course of steroid therapy (7 days) prior to discharge. MRI after 6 months and 2 years of surgery showed gross total resection without any recurrence [Figure 5]. On clinical follow-up, she has been asymptomatic for 4 years now.
Figure 5: (A) Postoperative MRI (T2WI) after 6 months showing complete resection of the lesion. (B) Postoperative MRI (post-contrast) after 6 months showing absence of recurrence

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  Discussion Top

The first case of a plasma cell pseudotumor involving the meninges was reported by Eimoto et al.[3] Intracerebral occurrence has been described involving the parenchyma, cavernous sinus, and choroid plexus.[4],[5]

On MRI, these lesions are iso to hypointense on T1 and hypointense on T2W images with a strong contrast enhancement. Dura may show either linear or focal nodular enhancement. These findings are very similar to that of meningiomas that tend to be isointense on T1 and T2 images with homogenous enhancement and a linear dural tail. Presence of atypical features should raise the index of suspicion. Besides meningiomas, hemangiopericytomas, dural-based metastases, and lymphomas can also mimic these findings.[6]

These are elusive lesions and often diagnosed only pathologically by a process of exclusion. They show a consistent, albeit variable amount of infiltration by lymphocytes and plasma cells besides granulated macrophages, mast cells, fibrosis, and other inflammatory cells like neutrophils. Granulated cells in xanthomatous pseudotumors are considered to be macrophages engulfing the granules released from mast cells.[1] The lymphoid infiltration is usually reactive in nature and shows polyclonal B or T cells. Rarely, dystrophic calcification may also be seen. Clonality analysis by PCR method is negative and hence malignant plasmacytoma can be ruled out. It is imperative to look for meningothelial/meningeal cell proliferation, which is characteristically absent, for excluding a plasma cell-lymphocytic rich meningioma.[7] Further, the epitheloid cells in a plasma cell granuloma are derivatives of epitheloid histiocytes whereas the epithelial cells in a meningioma are derivatives from the meningeal layer. This feature along with the presence of desmosomes and cytoplasmic interdigitations is suggestive of a meningioma over a plasma cell granuloma.

IPs may be confused with hypertrophic pachymeningitis (HP) which tends to involve all three meningeal layers. These two terms are often used interchangeably due to the subtle difference in pathology and lack of specific nomenclature. HP may be idiopathic or secondary in origin and histologically shows fibrous dural thickening and non-specific chronic inflammation. A newly described subset of this disease is associated with IgG4 infiltration. The ratio of IgG4 to IgG must be greater than 40% for its diagnosis,[8] apart from the presence of classical features such as lymphoplasmacytic infiltration, storiform architecture with fibrosis, and obliterative inflammation of veins. The basic pathology in both these conditions remains benign and non-neoplastic.

Inflammatory myofibroblastic tumor (IMT) is another closely related entity that also needs exclusion. They show a variable degree of mature plasma cells, lymphocytes, histiocytes, and spindle-like myofibroblasts which is the pathognomic feature. IHC shows polyclonal kappa and lambda light chain positivity (ruling out lymphoma and plamacytoma) and ALK1 staining in 40% of cases.

An algorithm for meningeal tumor mimics is provided in [Figure 6].
Figure 6: Algorithm depicting various subsets of meningeal tumor mimics

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Spontaneous regression of IP has been described and complete resection might not be imperative in such cases.[9] There is no consensus so far on the treatment. A course of corticosteroids after surgical resection has been advocated with favorable results.[10] Adjuvant use of immunomodulators and even radiotherapy has also been described with variable results.

  Conclusion Top

An IP involving the meninges is often a diagnosis of exclusion. Apart from histopathology, IHC study and clonal evaluation are mandatory for diagnosis. Surgical excision is avoidable and a short course of corticosteroid therapy may be beneficial.

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Conflicts of interest

There are no conflicts of interest.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

  References Top

Wentworth P, Lynch MJ, Fallis JC, Turner JA, Lowden JA, Conen PE Xanthomatous pseudotumor of lung: A case report with electron microscope and lipid studies. Cancer 1968;22:345-55.  Back to cited text no. 1
Kim DJ, Choi YS, Song YJ, Kim KU Intracranial plasma cell granuloma. J Korean Neurosurg Soc 2009;46:161-4.  Back to cited text no. 2
Eimoto T, Yanaka M, Kurosawa M, Ikeya F Plasma cell granuloma (inflammatory pseudotumor) of the spinal cord meninges: Report of a case. Cancer 1978;41:1929-36.  Back to cited text no. 3
McCall T, Fassett DR, Lyons G, Couldwell WT Inflammatory pseudotumor of the cavernous sinus and skull base. Neurosurg Rev 2006;29:194-200.  Back to cited text no. 4
Bramwit M, Kalina P, Rustia-Villa M Inflammatory pseudotumor of the choroid plexus. AJNR Am J Neuroradiol 1997;18:1307-9.  Back to cited text no. 5
Kim JH, Chang KH, Na DG, Park SH, Kim E, Han DH, et al. Imaging features of meningeal inflammatory myofibroblastic tumor. AJNR Am J Neuroradiol 2009;30:1261-7.  Back to cited text no. 6
Horten BC, Urich H, Stefoski D Meningiomas with conspicuous plasma cell-lymphocytic components: A report of five cases. Cancer 1979;43:258-64.  Back to cited text no. 7
Deshpande V, Zen Y, Chan JK, Yi EE, Sato Y, Yoshino T, et al. Consensus statement on the pathology of igg4-related disease. Mod Pathol 2012;25:1181-92.  Back to cited text no. 8
Roche PH, Figarella-Branger D, Pellet W Mixed meningeal and brain plasma-cell granuloma: An example of an unusual evolution. Acta Neurochir (Wien) 2004;146:69-72; discussion 72.  Back to cited text no. 9
Gollogly L, Sadzot B, Lejeune JP, Deprez M Meningeal inflammatory pseudotumour: A case report. Acta Neurol Belg 2001;101:116-20.  Back to cited text no. 10


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]


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