<p>Primary intestinal lymphangiectasia (PIL; Waldmann’s disease, ORPHA 90362) is a rare protein-losing enteropathy in which dilated intestinal lacteals leak chyle into the gut lumen. Cross-sectional imaging and lymphoscintigraphy have historically dominated assessment, while transabdominal B-mode intestinal ultrasound (IUS)—a cornerstone modality for inflammatory bowel disease—has remained almost unmapped in PIL. We conducted a PRISMA-ScR scoping review (Open Science Framework preregistration gfbc9) of all primary studies reporting transabdominal B-mode IUS in PIL, searching three bibliographic platforms (PubMed/MEDLINE, Ovid Multifile, Scopus) supplemented by forward and backward citation chasing. Studies using only extra-intestinal ultrasound, endoscopic ultrasound, those describing secondary lymphangiectasia or focal lymphangioma, and those using ultrasound only as procedural guidance for lymphangiography were excluded at full-text stage. Fifteen primary studies, published 1986–2026 across thirteen countries, met eligibility (nine paediatric, six adult). All fifteen reported per-patient B-mode IUS findings extractable for synthesis. A consistent sonographic signature emerged: diffuse, regular, slightly hypoechoic small-bowel-wall thickening with preserved five-layer stratification and prominent valvulae conniventes; dilated fluid-filled loops with reduced peristalsis; oedematous mesentery, variable ascites; and characteristically absent mesenteric lymphadenopathy (with two notable exceptions framed only as a research hypothesis). Diagnostic accuracy as a screening tool has been evaluated only in one study (<i>n</i> = 20: accuracy 80%, 95% CI 56.3–94.3%). We illustrate this signature in a 42-year-old woman with Hennekam syndrome and report quantitative B-mode IUS values as anecdotal single-observation—single sonographer, single device, single fasted time-point, mid-jejunal segment to motivate, prospective standardisation.</p>