The New American Commentary states:
The picture is that of a fall so severe as to open his body cavity and cause his inner organs (splanchna) to spill out. In consequence of this gory death the field became known by Jerusalem locals as Akeldama. For his non-Semitic readers, Luke translated the Aramaic word—“that is, Field of Blood.” Matthew gave a fuller account of Judas’s death. Despite significant differences in detail, the main emphases are the same in the two accounts—the purchase of a field with Judas’s blood money, the grisly death of the betrayer, the naming of the field “Field of Blood.
The Textual Commentary on the Greek New Testament says:
The enigmatic πρηνὴς γενόμενος (literally “having become prone”; AV, ASV, and RSV “falling headlong,” NEB “fell forward on the ground”) is interpreted variously in the early versions.
(1) The Latin versions attempt to harmonize the account in Acts with the statement in Matthew that Judas “went out and hanged himself” (Mt 27:5). The Old Latin version current in North Africa, according to a quotation by Augustine in his contra Felicem, i.4, seems to have read collum sibi alligavit et deiectus in faciem diruptus est medius, et effusa sunt omnia viscera eius (“he bound himself around the neck and, having fallen on his face, burst asunder in the midst, and all his bowels gushed out”). On the basis of this sole patristic witness Blass introduced καὶ κατέδησεν αὐτοῦ τὸν τράχηλον into his edition of the Roman form of the Acts, and Clark inserted the line καὶ τὸν τράχηλον κατέδησεν αὐτοῦ into his stichometric edition of Acts. Jerome, who may have known this rendering, reads in the Vulgate suspensus crepuit medius et diffusa sunt omnia viscera eius (“being hanged, he burst asunder in the midst, and all his bowels gushed out”).
(2) A different tradition is represented in the Armenian version and the Old Gregorian version; these describe Judas’s end thus: “Being swollen up he burst asunder and all his bowels gushed out.” What the Greek may have been from which this rendering was made is problematical. Papias, who according to tradition was a disciple of the apostle John, described Judas’s death with the word πρησθείς (from Epic πρήθειν, to swell out by blowing).
The Bible Knowledge Commentary says the following:
The account of Judas’ violent end in Acts 1:18 seems to contradict Matthew 27:5, which starkly says he “hanged himself.” One explanation is that Judas’ intestines quickly became swollen and distended after he hanged himself, so he burst open. Another explanation, more probable, is that Judas hanged himself over a cliff and the rope or branch of the tree he was using broke. When he fell to the rocks below, he “burst open.”
While these are plausible and possible understandings, an article published yesterday (view it at http://www.ligonier.org/blog/was-haman-hanged-or-impaled/, if you're interested) highlights a similar disparity of language in the OT, where some translations have Haman hanged and others have him impaled. The term which is translated as "hanged" in English probably does not actually relate to our western "hanging by the neck until dead". After all, Jesus is spoken of as "hanging ... on a tree" (Acts 5:30), and it's clear that this was not done using a noose.
In the case of Judas, we simply don't know. Clearly, even if "hanging" is used for Christ's crucifixion, Judas could not have crucified himself (or at least, I haven't figured out how he could have done that). It is also unlikely that he impaled himself, although we'd have a much better idea if we knew what the property he bought (and where he died) looked like. If he threw himself off a cliff and was impaled on a tree below, that would account for both descriptions. Alternately, he may indeed have hanged himself with a noose, and remained hanging until natural processes caused his body to burst (or some rather quicker supernaturally caused intervention - cf Acts 12:23).
Maybe not a completely satisfactory answer, but there are a few useful clues, I think...