Flat Posterior Cranial Fossa Affects Outcomes of Microvascular Decompression for Trigeminal Neuralgia

•MVD is an effective surgical procedure for TN; however, recurrence of TN after MVD is not rare.•We investigated 126 surgically treated primary TN patients with more than 1-year follow-up to identify the prognostic factors relevant to the recurrence of TN after MVD.•Type 2 TN and weak NVC were identified as negative prognostic factors for the outcomes of MVD for primary TN.•A relatively flatter PCF was associated with a poorer outcome following MVD for primary TN. Repeated NVC and arachnoid adhesions between the trigeminal nerve and surrounding structures could be facilitated by a flat PCF.