The Collaborative International Dictionary of English v.0.48:

Distension \Dis*ten"sion\, n.
   Same as Distention.
   [1913 Webster]

WordNet (r) 3.0 (2006):

distension
    n 1: the act of expanding by pressure from within [syn:
         distention, distension]
    2: the state of being stretched beyond normal dimensions [syn:
       dilatation, distension, distention]

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "distension":
   bloat, bloatedness, bloating, blowing up, boil, breaking point,
   bump, bunion, carbuncle, corn, cyst, diastole, dilatation,
   dilation, dropsy, edema, extension, extreme tension, flatulence,
   flatulency, flatus, furuncle, gassiness, inflation, intumescence,
   lump, meteorism, overdistension, overdrawing, overexpansion,
   overextension, overstrain, overstraining, overstretching, pimple,
   pock, puff, puffiness, puffing, pustule, rising, sebaceous cyst,
   snapping point, strain, straining, stretch, stretching, swell,
   swellage, swelling, swollenness, tension, tumefaction, tumescence,
   tumidity, tumidness, tumor, turgescence, turgescency, turgidity,
   turgidness, tympanism, tympany, wen, windiness