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Dorsal dermal sinus Conclusion delineate the pathology more accu- rately. Diagnose a dorsal dermal sinus if High-resolution spinal ultrasound is a the following findings are present: (t) valuable means of diagnosing sus- References a tract that connects the skin to the pected occult spinal dysraphic lesions intracanalicular space which may be 1. Korsvik H, KellerM. Sonography of occult dys- in neonates and infants before the raphism in neonates and infants with MR median or paramedian; this may imaging correlation. Radiographies 1992; 12: posterior spinal elements ossify. 297-306. communicate with the subarachnoid Ultrasound has numerous advan- 2. Nelson M jun. Ultrasonic evaluation of the 1 space; and (it) an associated lipoma, tages: it is portable and available with tethered cord syndrome. In: Yamada S, ed. Tethered Cord Syndrome. American Association epidermoid or dermoid with the sinus high-resolution capabilities, it is safe of Neurological Surgeons Publications tract. I Committee, 1996. and requires no sedation, and it is rel- 3. Hinshaw D jun., Engelhart J, Kaminsky C. atively inexpensive. When findings are Imaging of the tethered spinal cord. In: Yamada S, ed. Tethered Cord Syndrome. American confusing, abnormal or equivocal, Association of Neurological Surgeons then MR! must be performed to Publications Committee, 1996.

Ultrasound Hypertrophic technique A high frequency transducer pyloric (7 MHz) is used, preferably a linear or • vector probe (Acuson 128 XP/lO). an overview With the patient in the supine posi- tion start off scanning in the longitu- dinal section until the gall bladder is located,' The 'olive' of the hypertro- minating beyond the midline; I (iii) a H Grove phied musculature should be located Nst. Cert. Rsd. Ultrssound palpable 'olive' (pseudotumour) over medial to it. Visualisation is good an empty ;' (iv) age typically Department of Paediatric Radiology, Red Cross when the 'olive' has a foreshortened War Memorial Children's Hospital, University of 2 - 8 weeks; (v) male-to-female ratio Cape Town and Institute of Child Health appearance (Fig. I). 5:1; (vi) uncommon in black patients; The transducer now has to be (vit) often the male offspring of an rotated and angled so that it is aligned affected mother; (viii) gastric residual Definition with the long axis of the channel (Fig. > 10 ml;' and (ix) an association with 2). On this view, the beak sign can be The term hypertrophic pyloric steno- oesophageal atresia.' identified as on a contrast meal. sis (HPS) refers to hypertrophy of the Plain film If the stomach is too full, the chan- circular muscle of the that can findings nel is distorted and accurate measure- cause obstruction (HPO). ments won't be possible. In such a Clinical findings Plain film findings include the fol- case a nasogastric tube can be passed lowing: (i) gastric dilatation; (ii) to empty some of the contents. Clinical findings include the fol- paucity of small bowel and colonic air; Once the long axis is obtained, one lowing: (i) non-bilious projectile (iii) frothy gastric contents; (iv) should note the position of the trans- ; (it) peristaltic waves that absence of an air-filled duodenal bulb; ducer and turn it 90 degrees. This way can be seen travelling across the left (v) gastric pneumatosis; and (vi) nor- the bull's eye of the pyloric channel upper quandrant to the right and ter- mal appearance. can be identified end-on (Fig. 3).

48 SA JOURNAL OF RADIOLOGY. October 2001 TIPS FOR THE RADIOLOGIST

right side down,' we have been per- forming the study in a supine position at our institution. Glucose water can be given to evaluate antral emptying, but we haven't been finding this nec- essary. Conclusion While the upper gastro-intestinal Fig. 1. Obvious foreshortening of the pyloric chan- nel (cursors indicate the superior muscle thickness (VGl) series has been found to be less adjacent to the gall bladder) (arrow). Fig. 3. The bull's eye view of the pyloric channel in expensive than ultrasound," the latter its short axis (X's define the pyloric diameter. +'s define the muscle thickness). does not involve ionizing radiation and is a way of examining the pyloric muscle directly, rather than indirectly The rule of thumb is 5, 15 and 20 as in the VGl series. mm. If there is uncertainty the pyloric index can be worked out. References 1. VW Hilton S. Edwards DK. Practical Pediatric Pyloric index Radiology. 2nd ed. Philadelphia: WB Saunders. 1994: 303. The pyloric index may be calcula- 2. White MC. Langer JC. Don S. de Baun M. ted as follows: Sensitivity and cost minimization analysis of radiology versus olive for the diagno- pyloric index = wall thickness x 2 x 100 sis of hypertrophic pyloric stenosis. J Pediatr maximum diameter Surg 1998; 33: 913-917. 3. Finkelstein MS. Mandell GA. Tarbell K. Fig. 2. The long axis of the pyloric channel Is the Values greater than 50% and wall Hypertrophic pyloric stenosis: volumetric longest length that should be obtained. (GIB '" gall thickness 4 mm or more indicate measurement of nasogastric aspirate to deter- bladder. ST", stomach, X's define the pyloric diam- mine the inlage modality. Radiology 1990; 177: eter. +'s define the muscle wall thickness). HPS. 759-761. Values less than 35% and wall 4. Kilic N. Gurpinar A. Kiristioglu t, Dogruyol H. Association of oesophageal atresia and hyper- thickness 1 - 3 mm indicate the trophic pylorie stenosis. Acta Paediatr 2000; 89 Measurements absence of HPS. (1):118-119. 5. Teele RL. Share J. Gastro-duodenal ultrasono- At the Red Cross War Memorial Values greater than 50% and wall graphy. In: Bradlaw L. ed. Ultrasonography of Infants and Children. Philadelphia: WB Children's Hospital the following thickness 3 - 4 mm are equivocal for Saunders. 1991: 351. measurements are used: (lJ > 4 mm HPS and should be followed up. 6. Olson AD, Hernandez R. Hirsch] RB. The role of ultrasonography in the diagnosis of pylorie muscle thickness; (ii) > 12mm diam- Recommendations stenosis: a decision analysis. J Pediatr Surg 1998; eter (this includes two muscle walls 33: 76-681. Although the patient can be 7. Huike F.Campbell JR.Harrison MW. Campbell and mucosa); and (iii) > 14 mm TJ. Cost-effectiveness in diagnosing infantile length (up to 26 mm). scanned in the decubitus position, hypertrophic pyloric stenosis. J Pediatr Surg 1997; 32: 1604-1608.

49 SA JOU RNAL OF RADIOLOGY • October 2001