The Collaborative International Dictionary of English v.0.48:

Fistular \Fis"tu*lar\, a. [L. fistularis: cf. F. fistulaire.]
   Hollow and cylindrical, like a pipe or reed. --Johnson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

fistular
    adj 1: hollow and tube-shaped like a reed [syn: fistular,
           fistulate, fistulous]