IgG4-related hypertrophic pachymeningitis is one of the many manifestations of IgG4-related disease which represents a fibroinflammatory condition that can affect any organ. IgG4-related pachymeningitis is increasingly being recognized as the etiology of hypertrophic pachymeningitis, an entity which was once thought to be idiopathic.
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Epidemiology
It typically older men with a mean age of presentation of 59 years.
Head and neck manifestations of IgG4 disease are more common than hypertrophic pachymeningitis. Salivary gland involvement is the most common head and neck manifestation.
Clinical presentation
Patients may be asymptomatic, but if symptomatic, they commonly present with headaches. Symptoms may be related to mechanical compression of vascular or neural structures. Patients often present with systemic manifestations of the disease.
Pathology
Meningeal biopsy reveals "storiform" fibrosis with lymphoplasmacytic infiltration of IgG4-positive plasma cells (either > 10 cells/HPF or IgG4:IgG ratio >40%) and obliterative phlebitis.
Markers
Elevated serum IgG4 level and CSF IgG4 oligoclonal bands.
Radiographic features
In addition to radiographic features of IgG4-related hypertrophic pachymeningitis, which are detailed below, other associated head and neck manifestations of IgG4-related disease, such as IgG4-related-hypophysitis, lacrimal and salivary gland enlargement and inflammation, orbital pseudotumor, and perineural spread along trigeminal and other cranial nerves, may also be seen.
CT
Findings on CT can be very subtle. Plaque-like dural thickening may or may not be evident. Focal nodular thickening may mimic a meningioma.
MRI
The following signal characteristics are seen:
T1: isointense dural thickening
T1 C+ (Gd): homogeneous enhancement
T2/FLAIR: markedly hypointense due to underlying fibrosis (a reasonably specific imaging finding)
GRE/SWI: hypointense due to underlying fibrosis
FDG-PET
FDG-PET has limited utility for detecting pachymeningitis due to avid brain uptake of FDG and inferior spatial resolution of PET compared to MRI. FDG-PET can detect systemic/multiorgan manifestations of IgG4-related disease and can be utilized to assess for treatment response.
Treatment and prognosis
IgG4-related hypertrophic pachymeningitis is responsive to high dose steroids. Additionally, immunomodulators have shown variable efficacy.
Generally there is a favorable prognosis.
Differential diagnosis
infectious hypertrophic pachymeningitis
histiocytoses including Erdheim-Chester disease and Rosai-Dorfman disease
other granulomatous diseases including tuberculosis