Lymphoplasmacyte-rich meningioma

Lymphoplasmacyte-rich meningiomas (LPM) are rare histological variants of benign (WHO grade I) meningiomas, characterised by prominent lymphoplasmacytic infiltrates into the tumour, sometimes rendering the underlying meningothelial component inconspicuous. 

They also have an unusual clinical course (for meningiomas) which instead mimics an inflammatory process ¹.  Although reported numbers are few, and thus the features of these tumours have not been firmly established, they appear to differ from conventional meningiomas in a number of ways. 

Epidemiology

Unlike the usual meningiomas, lymphoplasmacyte-rich meningiomas are encountered more frequently in somewhat younger patients, without an obvious gender predilection ¹. 

Clinical presentation

Although the presenting symptom is similar to other intracranial masses (headache - most common, hemiparesis, seizure, dizziness, visual deficits), the course is more acute mimicking an intracranial inflammatory disease. Peripheral blood abnormalities are also detectable, including anaemia and polyclonal gammopathy, which normalize following resection ^2,4. 

Pathology

Although currently considered a variant of meningioma, the exact pathogenesis remains unclear, and whether LPMs arise as tumours or inflammatory masses remains to be elucidated ². In anycase these masses are characterised by meningothelial tumour cells (appearing similar/identical to a typical meningothelial meningioma) with abundant infiltrating lymphocytes and plasma cells ^1,3. Importantly, and supporting the contention that these are actually meningiomas with inflammatory infiltrates is that the inflammatory cells are not monoclonal / neoplastic ³. 

Radiographic features

Due to the relatively few cases reported it is difficult to make dogmatic statements about the imaging features of these tumours. 

In many instances they are solitary, resembling other variants of meningioma, but multiple masses have been reported, including involving the spine ⁴. They can have extensive relatively flat growth, similar to en plaque meningioma, and may have indistinct margins and vasogenic oedema in the adjacent brain parenchyma ⁵. 

Differential diagnosis

The differential diagnosis for this rare entity includes:

• other histological variants of meningioma
• hypertrophic pachymeningitis e.g. tuberculous pachymeningitis 
• meningeal metastases
• meningeal involvement with CNS lymphoma
• intracranial involvement with Erdheim Chester disease