Introduction The vascular membrane that forms around chronic subdural hematomas (cSDHs) has been implicated in the development and persistence of these lesions. However, the pathology underlying the formation of this membrane is poorly understood. There is mounting evidence that middle meningeal artery embolization (MMAE) can successfully cure cSDHs by occluding the meningeal arteries overlying the cSDH membrane, but the exact mechanism of this treatment is also poorly understood. We therefore sought to perform a histopathological characterization of the interface between the dura and cSDH membrane to begin to elucidate the underlying pathology of cSDH membranes and mechanism of MMAE.

Methods We retrospectively reviewed the clinical history and histology of 13 patients with cSDH who underwent surgical evacuation and resection of the dura with attached cSDH membrane. Specimens were formalin-fixed and paraffin-embedded. Standard H&E-stained sections were obtained for all cases and submitted for routine pathological evaluation. Brain autopsy dura samples from non-cSDH cases were used as controls.

Results All patients presented with symptomatic cSDH. The mean age was 76.8 years and nine patients were male. Seven patients had a definite history of a prior remote fall or head trauma preceding diagnosis of the cSDH ranging from two to 12 weeks. Two patients presented with bilateral cSDHs. Histological analysis of the dura-membrane interface in all cases revealed cSDH membranes consisting of exuberant organizing chronic hematoma with fibroblasts, small blood vessels, chronic inflammation, and hemosiderin deposits. Fresh hemorrhage was often found just beneath the cSDH membrane. Variable and focally pronounced vascular proliferation of small blood vessels was evident along the dura-membrane interface. Immunohistochemical analysis in select cases confirmed the presence of pronounced vascular proliferation including endothelial cells (+nuclear ERG staining) and vascular wall smooth muscle cells (+cytoplasmic SMA staining) along the dura-membrane interface. Such proliferation was not seen in normal control dura samples in brain autopsy material.

Conclusions The dural interface with a cSDH membrane is characterized by abnormal vascular proliferation. Such proliferation may be involved in the formation of the cSDH membrane and may play a role in the underlying mechanism of MMAE. Further investigation is warranted.

Disclosures M. Potts: None. M. Bitar: None. A. Alwakeal: None. P. Nazari: None. B. Jahromi: None.