An anxious mother brings her 5-week-old firstborn son to the pediatrician's office because he has been vomiting for the past five days. She notes that the vomiting occurs immediately after every feeding, is very forceful, and consists of curdled breast milk without any green or yellow discoloration. Despite the vomiting, the infant cries continuously and appears ravenously hungry, eagerly demanding to be fed again. On physical examination, the infant has slightly dry mucous membranes and a sunken anterior fontanelle. Palpation of the abdomen reveals a firm, mobile, 2-cm ovoid mass in the right upper quadrant. Which of the following is the most appropriate initial diagnostic test to confirm this patient's underlying condition?
- Abdominal ultrasoundAnswer
- BUpper gastrointestinal contrast series
- CPlain radiograph of the abdomen
- DComputed tomography scan of the abdomen
- EEsophagogastroduodenoscopy
Answer
Abdominal ultrasound
The clinical picture of a 3- to 6-week-old infant (often a firstborn male) presenting with projectile, nonbilious vomiting, persistent hunger, and a palpable 'olive-like' mass in the right upper quadrant is highly suggestive of infantile hypertrophic pyloric stenosis. The most appropriate initial imaging study to definitively confirm this diagnosis is an abdominal ultrasound. It is a highly sensitive, specific, and non-invasive modality that directly visualizes the hypertrophied pyloric muscle (typically characterized by a muscle thickness >4 mm and a pyloric channel length >14 mm) without exposing the infant to ionizing radiation.
Step-by-Step Solution
Key Concept
Diagnosis of Infantile Hypertrophic Pyloric Stenosis