Imaging description

Ultrasound is the preferred imaging modality for diagnosing hypertrophic pyloric stenosis (HPS). The primary sonographic features of HPS include pyloric muscular hypertrophy and channel elongation (Figures 93.1 and 93.2). There is variability in the literature for single wall pyloric muscular thickness diagnostic of HPS, ranging from 3.0 to 4.5 mm [1–6]. Blumhagen and Noble evaluated 326 sonograms in vomiting infants to assess sonographic criteria for HPS diagnosis. They found muscle thickness in HPS patients measured 4.8 +/− 0.6 mm, compared with 1.8 +/− 0.4 mm in normal children [2]. At our institution, single wall thickness exceeding 3.0 mm is consistent with HPS. Similarly, there is a reported range of pyloric channel length consistent with HPS. Most authors consider cutoffs between 14 and 17 mm as diagnostic for HPS [1–6]. Rohrschneider et al. reported a 94% accuracy rate using a 15 mm channel length to differentiate normal patients (< 15 mm) from those with HPS (> 15 mm) [5]. In patients with HPS there is often crowding and thickening of the pyloric mucosa, which may protrude into the gastric antrum [1].

Pylorospasm (PS) can mimic HPS clinically as well as on both upper GI (GI) and ultrasound. This condition results in an intermittent narrowing of the pyloric channel, with resultant transient gastric outlet obstruction causing forceful non-bilious emesis. There may be significant overlap in pyloric measurements between HPS and PS. In a 1998 series of 34 patients with HPS by Cohen et al., 18 children had pyloric thicknesses of greater than 4 mm, and 19 children had pyloric lengths greater than 14 mm. Pylorospasm can therefore serve as a major pitfall for diagnosing true pyloric stenosis on ultrasound, particularly when relying on static measurements alone [7, 8].