340 CLINICAL RADIOLOGY

Correspondence Letters are published at the discretion of the Editor. Opinions expressed by correspondents are not necessarily those of the Editor. Unduly long letters may be returned to the authors for shortening. Letters in response to a paper may be sent to the author of the paper so that the reply can be published in the same issue.

Letters should be typed double spaced and should be signed by all authors personally. References should be given in the style specified in the Instruction to Authors at the front of the Journal.

BOWEL PREPARATION AND THE PILL

SlR- I had the same experience as Dr Hale (1985) last year and discovered that the action of laxatives should not effect the absorption of the contraceptive pill. Oestrogens are fat-soluble and very readily absorbed through mucous membranes. Their absorp- tion is prompt and quite complete (Goodman and Gilman, 1980)

Patients taking the contraceptive pill are advised, if they develop vomiting or diarrhoea, to use an additional contraceptive method for the remainder of the cycle for two reasons. First, they may vomit the oestrogen before it is absorbed and, secondly, acute infectious enteritis can be associated with malabsorption of fat (Cecil, 1979).

Laxatives act by bulking, fluid retention in the gut lumen, increasing mucosal permeability or increasing bowel activity. The laxatives used in bowel preparation in radiology make use of the last three actions. Castor oil, which is rarely used, will affect the absorption of lipids or fat-soluble drugs and might, therefore, affect oestrogen absorption. Fluid retention in the gut lumen (e.g. magnesium salts as in Picolax; Nordic Pharmaceuticals) would have little effect on oestrogen absorption as this effect is most marked in the distal bowel. The chemical laxatives such as the diphenyl- methanes (e.g. bisacodyl) and the anthraquinones (e.g. senna as in X-Prep; Schering) act on the large bowel and have little effect on the small bowel (Goodman and Gilman, 1980).

If a pill is not taken, or there is failure of absorption, the pregnancy rate is about 2.5% per 100 woman years (Loraine and Bell, 1968). It should be noted that the 10-day rule would be of no help in preventing pregnancy in a patient who had failed to absorb her contraceptive pill

W. E. SVENSSON

References

Cecil, R. L. (1979).

Deparmwnt of Radiology Royal Free Hospital

London

Textbook of Medicine, 15th edn. W. B. Saunders, Philadelphia.

Goodman, L. S. & Gilman, A. (1980). The Pharmacological Basis of Therapeutics, 6th edn. Macmillan, New York.

Hale, M. (1985). Bowel preparation and the pill (letter). Clinical Radiology, 36, 100.

Loraine, J.A. & Bell, E.T. (1968). Fertility and Contraception in the Human Female, 1st edn. E. & S. Livingstone, Edinburgh.

THE ERECT ABDOMINAL RADIOGRAPH IN INTESTINAL OBSTRUCTION

S~R - I read the recent paper by Simpson et al. (1985) with interest, because it confirms my own impressions of the value of the erect abdominal film, but also because of the following observations. The authors present two tables which fail to indicate that the figures shown are the number of patients in Table 1 and percentage of patients in Table 2. Initially, I was misled by this. The statement that the differences in diagnostic accuracy between the supine film alone and the supine and erect films combined is 'not significant for any individual observer or for the mean value' is not supported by any statement of the statistical analysis used. Finally, they state that the erect film should be requested 'where the complication of perforation is thought to accompany the obstruction'. This is presumably to attempt to show air under the diaphragm. However, the erect film has been shown to be inferior to the erect chest film

or the left lateral decubitus film in the diagnosis of free intraperi- toneal gas (Miller and Nelson, 1971).

ANTHONY P. CORAL

References

Department of Radiology St Mary's Hospital

London

Miller, R. E. & Nelson, S. W. (1971). The roentgenologic demon- stration of tiny amounts of free intraperitoneal gas: experimental and clinical studies. American Journal of Roentgenology, 112, 574-585.

Simpson, A., Sandeman, D., Nixon, S. J., Goulbourne, I. A., Grieve, D. C. & Macintyre, I. M. C. (1985). The value of an erect abdominal radiograph in the diagnosis of intestinal obstruc- tion. Clinical Radiology, 36, 41-42.

Sin-In reply to Dr Coral, I note his points with regard to the tables. I apologise for the inconvenience this may have caused. As far as the statistical analysis used is concerned, this was a Fisher's exact test which gave p values of greater than 0.1 for the mean value and greater than 0.05 for the best observer result. With regard to the erect film as a demonstration of free gas in the peritoneal cavity, I accept Dr Coral's comments.

ALEXANDER SIMPSON (for SIMPSON, SANDEMAN, Department of General Surgery NIXON, GOULBOURNE, GRIEVE Leith Hospital & MACINTYRE) Edinburgh

DIAGNOSIS AND REDUCTION OF AN INTUSSUSCEPTION UNDER ULTRASOUND GUIDANCE: A NEW TECHNIQUE?

SIR - There have been a number of reports in the literature on the ultrasound appearances of an intussusception, following the first descriptions by Weissberg et al. (1977) and Burke and Clarke (1977).

Recently, we attempted a hydrostatic reduction of an ilio-colic intussusception under ultrasound guidance, using a water-soluble contrast medium. The leading edge of the intussusceptum was clearly outlined. The intussusceptum could be seen becoming smaller in size as the reduction proceeded. Using ultrasound guidance only, it was possible to determine the end point, when it was thought that a successful reduction had been achieved. A radiograph at this stage confirmed reduction of the intussusception.

The choice of barium as contrast medium is inappropriate due to its high reflectivity of the ultrasound beam. The use of Urografin 150 (sodium and meglumine diatrizoate; Schering AG) was advantageous in two respects: (1) the ease of visualisation of the leading edge of the intussusceptum and (2) the determination of the end-point, enabled by the visualisation of movement of the contrast medium, due to the presence of microbubbles in it.

We have not seen this procedure described in the literature before and would appreciate readers' comments.

A. A. BOLIA Department of Radiology

Children's Hospital Western Bank

Sheffield

References

Burke, L. S. & Clarke, E. (1977). Ilio-colic intussusception, a case report. Journal of Clinical Ultrasound, 5, 346-347.

Weissberg, D. L., Scheible, W. & Leopold, G. R. (1977). Ultra- sonographic appearance of adult intussusception. Radiology, 124, 791-792.