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Intracranial Idiopathic Inflammatory Pseudotumor


KEY FACTS

Terminology

  • Definition: Nonspecific, nonneoplastic benign inflammatory lesion without identifiable local or systemic causes characterized by polymorphous lymphoplasmacytic infiltrate

  • Idiopathic orbital inflammation

    • May involve any part(s) of orbit

  • Idiopathic extraorbital inflammation

    • Intracranial involvement : Spread through superior orbital fissure (SOF) or optic canal (OC)

      • –

        Cavernous sinus, dura, Meckel cave

    • Skull base-extracranial involvement : Spreads from inferior orbital fissure (IOF) or through orbital wall

      • –

        Anterior skull base, sinuses, nasopharyngeal spaces

  • IgG4-related disease: Subgroup of idiopathic inflammation with systemic involvement

    • Intracranial noncontiguous sites: Pituitary, infundibulum

    • Extracranial noncontiguous H&N sites: Parotid, submandibular glands, thyroid

Imaging

  • T1WI C+ FS MR: Diffusely enhancing, infiltrating mass

    • Extends from orbit through SOF ± OC to cavernous sinus, dura, Meckel cave

    • Extends through IOF to pterygopalatine fossa, nose, deep nasopharyngeal spaces

  • T2: Iso- to hypointense lesion; ↑ fibrosis, ↓ intensity

Top Differential Diagnoses

  • En plaque meningioma

  • Meningeal non-Hodgkin lymphoma

  • Nasopharyngeal carcinoma

  • Neurosarcoid

Clinical Issues

  • Symptoms: Painful proptosis ± headaches ± cranial neuropathies (Tolosa Hunt syndrome)

  • Diagnosis of exclusion (draw IgG4 levels; biopsy)

  • Treatment: High-dose systemic steroids

Axial T1WI C+ FS MR shows a focus of enhancing idiopathic extraorbital inflammation (IEI) involving the right cavernous sinus
with subtle narrowing
of the intracavernous internal carotid artery.

Axial T2WI MR in the same patient reveals that an idiopathic orbital inflammation lesion
connects to the cavernous sinus IEI
through the superior orbital fissure
. Both areas of idiopathic inflammation are hypointense due to the fibrosis often found within this lesion.

Axial T1WI C+ FS MR through the orbits shows enlarged, enhancing orbital rectus muscles
connecting through the superior orbital fissure
with the cavernous sinus
and Meckel cave
. First impression of adenoid cystic carcinoma gave way to biopsy-proven idiopathic inflammation with both intraorbital and intracranial components.

Axial T1WI C+ FS MR in the same patient shows the lesion invading inferiorly through the inferior orbital fissure into the pterygopalatine fossa
and nose
.

TERMINOLOGY

Abbreviations

  • Idiopathic extraorbital inflammation (IEI)

Synonyms

  • Idiopathic inflammatory disease, Tolosa-Hunt syndrome, hypertrophic cranial pachymeningitis, plasma cell granuloma

Definitions

  • Nonspecific, nonneoplastic benign inflammatory lesion without identifiable local or systemic causes characterized by polymorphous lymphoplasmacytic infiltrate

    • IgG4-related disease (IgG4-RD): Subgroup of idiopathic orbital inflammation (IOI) IEI lesions where multisystem manifestation are present with positive cell immunostain showing IgG4-rich plasma cells

IMAGING

General Features

  • Best diagnostic clue

    • IOI combined with contiguous extraorbital (intracranial, skull base, or extracranial) idiopathic inflammation

  • Location

    • IOI

      • –

        May involve any part(s) of orbit

    • IEI

      • –

        Intracranial involvement : Spread through superior orbital fissure (SOF) or optic canal (OC)

        • □

          Cavernous sinus

        • □

          Dural thickening (previously called “pachymeningitis”)

        • □

          Meckel cave area

        • □

          Noncontiguous IgG4-RD: Pituitary, infundibulum

      • –

        Skull base-extracranial involvement : Spreads from inferior orbital fissure (IOF) or through orbital wall

        • □

          Pterygopalatine fossa, nose, sinuses

        • □

          Anterior skull base, sinuses

        • □

          Deep spaces of nasopharynx

        • □

          Noncontiguous IgG4-RD: Parotid, submandibular glands, thyroid

  • Size

    • Small, subtle to very extensive extraorbital involvement

    • Skull base and extracranial soft tissue masses may be large (many centimeters)

  • Morphology

    • Soft tissue infiltrating lesions mimic invasive malignancy

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