Teaching Case

A 2-month-old boy presented with persistent non-bilious vomiting since second week of life.

On ultrasonography, hypoechoic hypertrophied muscle layer (Fig. 1a) and hyperechoic mucosa of pylorus is noted. The pyloric wall measures 4.2 mm in thickness, the pyloric canal measures 18.7 mm in length and 13 mm in transverse diameter confirming pyloric hypertrophy. Sonographic target sign on transverse view (Fig. 1d) and cervix sign on longitudinal view (Fig. 1e) are also noted. Additional investigations were done. Plain radiograph AP view shows gaseous distension of the stomach (Fig. 2a). On upper gastrointestinal barium study, the pylorus appears elongated with narrowed lumen (string sign – Fig. 2b) and indents barium-filled antrum (shoulder sign – Fig. 2c).

Hypertrophic pyloric stenosis (HPS) is a common cause of vomiting in neonates and young infants. Its incidence is 3 per 1000 live births per year; however, ethnic and geographic variations have been recorded [1]. It has a male preponderance with male: female ratio of 4:1 [2]. HPS is characterised by hyperplasia and hypertrophy of muscle and mucosa of pylorus. Its aetiology is still unclear. Clinical presentation of HPS is non-bilious projectile vomiting with olive-shaped mass palpable in the epigastrium. Although clinically regarded as typical sign for the clinical diagnosis of the majority of HPS, it is not seen commonly. Differential diagnoses include pylorospasm and gastroesophageal reflux. Pylorospasm may show thickened pylorus but depiction of the changes in measurements of the pyloric wall and length in real-time imaging study points towards pylorospasm. Gastroesophageal reflux does not show pyloric muscle hypertrophy. Imaging techniques help in accurate diagnosis of HPS. Sonography is the modality of choice for HPS with a sensitivity of 98% and specificity of 100% [3]. A sonographic diagnostic criterion for HPS is: Pyloric muscle wall thickness > 3 mm, Pyloric canal length > 15 mm and Pylorus diameter > 12 mm [4]. The pylorus muscle wall thickness is the main criterion for the diagnosis of HPS. It appears as hypoechoic in all positive cases. Sonographic signs include: 1) Target sign (thickened pylorus on transverse scan); 2) Cervix sign (Bulging of pyloric muscle into fluid-filled antrum); 3) Antral nipple sign (protrusion of pyloric mucosa into the antrum). Another significant parameter for the diagnosis of HPS is presence of vascularity in the hypertrophied pyloric wall [4]. Normal pyloric wall shows no vascularity. The only limitation associated with sonographic diagnosis is its operator dependency. Fluoroscopy-guided upper gastrointestinal contrast study also depicts typical signs of pyloric hypertrophy which include, a) String sign (thin strip of barium passing through narrowed pyloric canal); b) Beak sign (beak-shaped entrance of antrum into pylorus); c) Shoulder sign (bulging of pyloric muscle on the barium-filled antrum); d) Caterpillar sign (due to peristaltic waves in the stomach). Management of HPS includes rehydration, electrolyte correction followed by surgical intervention. Surgical division of hypertrophied muscle with sparing of the mucosa is called pyloromyotomy, which can be an open (Ramstedt’s pyloromyotomy) or laparoscopic procedure. In this case, open procedure was performed and was declared successful.
TEACHING POINT:
With use of the proper technique and evaluation methods, sonography is the modality of choice for diagnosing HPS.