From the Guidelines
Leptomeningeal enhancement has several rare causes beyond the common etiologies of infection, malignancy, and inflammatory conditions, including neurosarcoidosis, intravascular lymphoma, Vogt-Koyanagi-Harada syndrome, hypertrophic pachymeningitis, superficial siderosis, neurocutaneous melanosis, and IgG4-related disease, as reported in various studies 1. These uncommon causes should be considered in cases where leptomeningeal enhancement is present but common causes have been excluded. Some key points to consider include:
- Neurosarcoidosis can present with leptomeningeal involvement in 5-10% of cases 1
- Intravascular lymphoma is a rare subtype of non-Hodgkin lymphoma that can affect the leptomeninges 1
- Vogt-Koyanagi-Harada syndrome is an autoimmune disorder affecting melanocyte-rich tissues that can cause leptomeningeal enhancement particularly at the posterior fossa 1
- Hypertrophic pachymeningitis is a condition characterized by thickening of the dura mater that may occasionally extend to involve the leptomeninges 1
- Superficial siderosis can mimic leptomeningeal enhancement on MRI due to hemosiderin deposition 1
- Neurocutaneous melanosis is a rare congenital disorder that may present with leptomeningeal melanosis that enhances on contrast imaging 1
- IgG4-related disease is a systemic fibroinflammatory condition that can rarely affect the leptomeninges 1 Diagnosis typically requires correlation with clinical presentation, laboratory findings, and sometimes biopsy for definitive identification, as emphasized in recent guidelines 1. It is essential to consider these rare causes and to use a combination of clinical, laboratory, and imaging findings to establish a diagnosis, as highlighted in the most recent study 1.
From the Research
Rare Causes of Leptomeningeal Enhancement
The following are rare causes of leptomeningeal enhancement:
- Primary leptomeningeal lymphoma, including ALK-positive anaplastic large cell lymphoma (ALCL) and primary effusion lymphoma (PEL) 2
- MOG-IgG-associated encephalomyelitis, which can present with bilateral symmetrical deep gray matter involvement and leptomeningeal enhancement 3
- Neurosarcoidosis, which can mimic malignancy and present with leptomeningeal enhancement 4
- Leptomeningeal myelomatosis, a rare complication of multiple myeloma characterized by widespread nodular leptomeningeal enhancement 5
- Leptomeningeal melanocytosis, a rare cause of seizure in the pediatric population characterized by progression of leptomeningeal enhancement 6
Characteristics of Rare Causes
Some key characteristics of these rare causes include:
- Primary leptomeningeal lymphoma: exclusive leptomeningeal disease, lymphocytic pleocytosis, and brisk mitotic activity 2
- MOG-IgG-associated encephalomyelitis: bilateral symmetrical deep gray matter involvement, leptomeningeal enhancement, and positive serum MOG IgG 3
- Neurosarcoidosis: lymphocytic pleocytosis, hypoglycorrhachia, and hyperproteinorrachia, with noncaseating granulomatous inflammation on biopsy 4
- Leptomeningeal myelomatosis: widespread nodular leptomeningeal enhancement, involvement of supra- and sub-tentorial regions, and poor prognosis 5
- Leptomeningeal melanocytosis: progression of leptomeningeal enhancement, increased seizure activity, and confirmation of diagnosis by biopsy 6