Oreongsan, an herbal medicine prescription developed as a new alternative treatment in patients with chronic subdural hematoma: a narrative review.

Oreongsan (ORS), which is composed of Polyporus, Alismatis Rhizoma, Atractylodis Rhizoma, Poria (Hoelen), and Cinnamomi Cortex Spissus, has been used as treatment in patients with various symptoms such as thirst, diminished urination, edema, hangover, and diarrhea. ORS is the representative prescription of the (isu) effect (translated from Korean as "induce diuresis"), which traditionally means the effect of controlling the water balance. Advancement of modern science has enabled the determination of the action mechanism of herbal medicine complexes. As a result, ORS has been used in the treatment of patients with chronic subdural hematoma (CSDH), representing a novel indication. ORS inhibits the upregulation of aquaporin-4, which is involved in the development of brain edema in the central nervous system. Both aquaporin-1 and aquaporin-4 are expressed in the outer membrane of the CSDH; through its effect as aquaporin-4 inhibitor, ORS prevents the inflow of fluid into the hematoma, thereby preventing the development and recurrence of hematoma. In this study, we reviewed the relationship between the isu effect of ORS and aquaporin, conservative treatment approach in patients with CSDH, and the prevention of recurrence in patients undergoing combined burr hole surgery and treatment with ORS.