The Collaborative International Dictionary of English v.0.48:

Fistulous \Fis"tu*lous\, a. [Cf. F. fistuleux.]
   1. Having the form or nature of a fistula; as, a fistulous
      ulcer.
      [1913 Webster]

   2. Hollow, like a pipe or reed; fistulose. --Lindley.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fistulous
    adj 1: of or pertaining to or resembling a fistula
    2: hollow and tube-shaped like a reed [syn: fistular,
       fistulate, fistulous]