The Evaluation of Palpable Thigh Nodularity in Vaccination-age Children - Differentiating Vaccination Granulomas from Other Causes.

Palpable thigh nodularity is a relatively frequent indication for imaging of vaccination-age children, with patients often referred by their community physician or general practitioner. Ultrasound (US) is the imaging modality of choice to delineate the abnormality, and we present a number of characteristic findings that permit the radiologist and pediatrician to accurately identify the cause. A retrospective review was performed at the largest children's hospital in a European country between 2015 and 2017 over a 30-month period. A search was performed of the hospital's Picture Archiving and Communication System (PACS) for all children referred for a soft-tissue, upper limb, or lower limb US between January 2015 and July 2017. The findings were collated and stored in a spreadsheet. Nine patients were identified who developed subcutaneous nodules in the thigh at some point during their childhood vaccination schedule. Three of these patients had clinical histories strongly suggestive of a diagnosis of abscess or foreign body. The remaining six patients were selected for more in-depth analysis. Four of these patients had US features consistent with vaccination granuloma. Two patients were ultimately diagnosed with venolymphatic malformations. Palpable thigh nodularity in a child of vaccination age is encountered with a reasonable frequency. When encountered, granulomas tend to be located within the subcutaneous tissues, and we postulate that this is due to erroneous administration of a vaccine into the subcutis rather than into the muscle.