The doctor suspected his headache was caused by a meningeal infection.

meningeal 是由名词 meninges（脑膜）加上形容词后缀 -al 构成的形容词。meninges 指包裹大脑和脊髓的三层保护膜，-al 表示"与...相关的"。meningeal 意思是"脑膜的"，描述与脑膜相关的事物。