TIPS FOR THE RADIOLOGIST Dorsal dermal sinus Diagnose a dorsal dermal sinus if the following findings are present: (t) a tract that connects the skin to the intracanalicular space which may be median or paramedian; this may communicate with the subarachnoid space; 1 and (it) an associated lipoma, epidermoid or dermoid with the sinus tract. I Conclusion High-resolution spinal ultrasound is a valuable means of diagnosing sus- pected occult spinal dysraphic lesions in neonates and infants before the posterior spinal elements ossify. Ultrasound has numerous advan- tages: it is portable and available with high-resolution capabilities, it is safe and requires no sedation, and it is rel- atively inexpensive. When findings are confusing, abnormal or equivocal, then MR! must be performed to delineate the pathology more accu- rately. References 1. Korsvik H, KellerM. Sonography of occult dys- raphism in neonates and infants with MR imaging correlation. Radiographies 1992; 12: 297-306. 2. Nelson M jun. Ultrasonic evaluation of the tethered cord syndrome. In: Yamada S, ed. Tethered Cord Syndrome. American Association of Neurological Surgeons Publications Committee, 1996. 3. Hinshaw D jun., Engelhart J, Kaminsky C. Imaging of the tethered spinal cord. In: Yamada S, ed. Tethered Cord Syndrome. American Association of Neurological Surgeons Publications Committee, 1996. Hypertrophic pyloric stenosis •an overview H Grove Nst. Cert. Rsd. Ultrssound Department of Paediatric Radiology, Red Cross War Memorial Children's Hospital, University of Cape Town and Institute of Child Health Definition The term hypertrophic pyloric steno- sis (HPS) refers to hypertrophy of the circular muscle of the pylorus that can cause obstruction (HPO). Clinical findings Clinical findings include the fol- lowing: (i) non-bilious projectile vomiting; (it) peristaltic waves that can be seen travelling across the left upper quandrant to the right and ter- minating beyond the midline; I (iii) a palpable 'olive' (pseudotumour) over an empty stomach;' (iv) age typically 2 - 8 weeks; (v) male-to-female ratio 5:1; (vi) uncommon in black patients; (vit) often the male offspring of an affected mother; (viii) gastric residual > 10 ml;' and (ix) an association with oesophageal atresia.' Plain film findings Plain film findings include the fol- lowing: (i) gastric dilatation; (ii) paucity of small bowel and colonic air; (iii) frothy gastric contents; (iv) absence of an air-filled duodenal bulb; (v) gastric pneumatosis; and (vi) nor- mal appearance. 48 SA JOURNAL OF RADIOLOGY. October 2001 Ultrasound technique A high frequency transducer (7 MHz) is used, preferably a linear or vector probe (Acuson 128 XP/lO). 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- phied musculature should be located medial to it. Visualisation is good when the 'olive' has a foreshortened appearance (Fig. I). The transducer now has to be rotated and angled so that it is aligned with the long axis of the channel (Fig. 2). On this view, the beak sign can be identified as on a contrast meal. If the stomach is too full, the chan- nel is distorted and accurate measure- ments won't be possible. In such a case a nasogastric tube can be passed to empty some of the contents. Once the long axis is obtained, one should note the position of the trans- ducer and turn it 90 degrees. This way the bull's eye of the pyloric channel can be identified end-on (Fig. 3). TIPS FOR THE RADIOLOGIST Fig. 1. Obvious foreshortening of the pyloric chan- nel (cursors indicate the superior muscle thickness adjacent to the gall bladder) (arrow). Fig. 2. The long axis of the pyloric channel Is the longest length that should be obtained. (GIB '" gall bladder. ST", stomach, X's define the pyloric diam- eter. +'s define the muscle wall thickness). Measurements At the Red Cross War Memorial Children's Hospital the following measurements are used: (lJ > 4 mm muscle thickness; (ii) > 12 mm diam- eter (this includes two muscle walls and mucosa); and (iii) > 14 mm length (up to 26 mm). Fig. 3. The bull's eye view of the pyloric channel in its short axis (X's define the pyloric diameter. +'s define the muscle thickness). The rule of thumb is 5, 15 and 20 mm. If there is uncertainty the pyloric index can be worked out. Pyloric index The pyloric index may be calcula- ted as follows: pyloric index = wall thickness x 2 x 100 maximum diameter Values greater than 50% and wall thickness 4 mm or more indicate HPS. Values less than 35% and wall thickness 1 - 3 mm indicate the absence of HPS. Values greater than 50% and wall thickness 3 - 4 mm are equivocal for HPS and should be followed up. Recommendations Although the patient can be scanned in the decubitus position, 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 (VGl) series has been found to be less expensive than ultrasound," the latter does not involve ionizing radiation and is a way of examining the pyloric muscle directly, rather than indirectly as in the VGl series. References 1. VW Hilton S. Edwards DK. Practical Pediatric Radiology. 2nd ed. Philadelphia: WB Saunders. 1994: 303. 2. White MC. Langer JC. Don S. de Baun M. Sensitivity and cost minimization analysis of radiology versus olive palpation for the diagno- sis of hypertrophic pyloric stenosis. J Pediatr Surg 1998; 33: 913-917. 3. Finkelstein MS. Mandell GA. Tarbell K. Hypertrophic pyloric stenosis: volumetric measurement of nasogastric aspirate to deter- mine the inlage modality. Radiology 1990; 177: 759-761. 4. Kilic N. Gurpinar A. Kiristioglu t, Dogruyol H. Association of oesophageal atresia and hyper- trophic pylorie stenosis. Acta Paediatr 2000; 89 (1):118-119. 5. Teele RL. Share J. Gastro-duodenal ultrasono- graphy. In: Bradlaw L. ed. Ultrasonography of Infants and Children. Philadelphia: WB Saunders. 1991: 351. 6. Olson AD, Hernandez R. Hirsch] RB. The role of ultrasonography in the diagnosis of pylorie stenosis: a decision analysis. J Pediatr Surg 1998; 33: 76-681. 7. Huike F.Campbell JR. Harrison MW. Campbell TJ. Cost-effectiveness in diagnosing infantile hypertrophic pyloric stenosis. J Pediatr Surg 1997; 32: 1604-1608. 49 SA JOU RNAL OF RADIOLOGY • October 2001