ABSTRACT
PURPOSE: The purpose of this study was to report the sonographic findings of neonatal coccygeal abscess,previously not described. MATERIALS AND METHODS: Eighteen neonates (5-18 days old) presented with swelling in thecoccygeal area and by either open drainage (n=13) or follow-up after antibiotic therapy (n=5), this was diagnosedas coccygeal abscess. We retrospectively reviewed the size, shape, location, echo pattern and marginalcharacteristics of the abscesses, as seen on sonography, as well as their intradural content and relationship withthe spine. Additional MR images (n=5) were separately reviewed. RESULTS: Mean longest diameter of the abscesseswas 1.5cm (range, 0.8-2.3); they were oval or round and located in the subcutaneous fat layer. Echogenicitycompared with surrounding fat varied: in nine patients it was isoechoic, and in nine, hypoechoic. Internalechogenicity was homogenous in 14 patients and heterogeneous in four, and in seven cases, the margin of theabscess was well demarcated. Intradural structure and bony spines were normal, and the possibility of spinaldysraphism, could thus be excluded. All cases except one were correctly diagnosed by sonography and clinicalfindings; on sonography, the echogenicity of one lesion was exactly the same as that of lipoma, and it was thusmisdiagnosed. In cases where sonography revealed an isoechoic mass, the use of MR excluded the possibility oflipoma. Three of five cases showed marginal or diffuse enhancement on contrast enhanced MR images. CONCLUSION: Coccygeal absesses were confined to the subcutaneous fat layer and were either iso- or hypoechoic compared. withsurrounding fat. In neonates, abscess formation in the coccygeal area is possible, and coccygeal abscess shouldtherefore be included in the differentiation of coccygeal masses.