Partial visualization of appendix on ultrasound: What does it mean in the child with suspected appendicitis?

Background: Visualization of the entire appendix, including the tip, is thought, but has not been demonstrated, to be important for exclusion of appendicitis by ultrasound. Objective: To determine if incomplete visualization of the appendix has negative clinical ramifications including missed appendicitis. Methods: Under IRB approval we retrospectively reviewed right lower quadrant ultrasound reports from January 2017 to December 2020 to identify examinations with impressions of full visualization of the normal appendix, non-visualization of the appendix with and without secondary findings of appendicitis, and partial visualization of the appendix. Electronic health records were reviewed for follow-up imaging within 48 h, and surgery with pathology reports (if available). Results: 12,193 examinations were included. 4171 (34.2 %) had full visualization of a normal appendix, 5369 (44.0 %) had non-visualization with no secondary findings, and 234 (1.9 %) had non-visualization with secondary findings, The frequencies of appendicitis in these three groups were 34 (0.8 %), 283 (5.3 %), and 127 (54.3 %) respectively. The appendix was partially visualized in 338 (2.8 %) patients with secondary findings present in 53 (15.6 %). Partial visualization without secondary findings had a similar frequency (4.9 %, 14/285) of appendicitis to non-visualized appendix without secondary findings (p = 0.797) and a higher frequency than full visualization of a normal appendix (p < 0.0001). Partial visualization with secondary findings had similar rates (54.7 %, 29/53) to non-visualized appendix with secondary findings (p = 0.953). Conclusion: Partial visualization of the appendix with ultrasound (with and without secondary findings) is associated with similar frequencies of appendicitis as non-visualization of appendix (with and without secondary findings).