Sonography of subcutaneous nodules following immunization with histopathological correlation: a three-case series

Abstract

Subcutaneous nodules are a rare adverse event following immunization frequently associated with suboptimal injection procedures and aluminium-containing vaccines. We present three cases of subcutaneous nodules following immunization describing their clinical signs, histopathological features and ultrasound findings and demonstrating the use of sonography as an aid to the diagnosis of this entity.

Keywords: Immunization; Subcutaneous nodules; Ultrasound; Vaccines.

Fig. 1

Sonography demonstrated a subcutaneous teardrop-shaped, hypoechoic nodule with sharp margins and an elongated central echoic area (*). A small tract arising from the upper portion of the nodule to the subcutis was also observed (arrow). The surrounding adipose tissue appeared hazy and with increased echogenicity. The color-Doppler assessment showed increased vascularity around the periphery of the lesion

Fig. 2

a Histological examination of a skin fragment from case 1 punch biopsy (haematoxylin and eosin stain). b Medium power magnification reveals a granulomatous reaction in subcutaneous tissue. c Higher-power magnification shows histiocytes with violaceous granular cytoplasm

Fig. 3

a The patient presented swelling in her right upper arm, tender and indurated on palpation. b, c The ultrasound exam revealed two hypodermal hypoechoic nodules with well-defined margins and posterior acoustic shadowing, the largest measuring 30 mm. The surrounding adipose tissue had a diffuse increased echogenicity (*). d No vascularization was detected with color-Doppler

Fig. 4

a Histological examination of a skin fragment from case 2 punch biopsy (haematoxylin and eosin stain). b Medium power magnification reveals dense pseudonodular inflammatory infiltrates in the dermis, including lymphoid follicles with germinal centres. c Higher-power magnification shows histiocytes with violaceous granular cytoplasm and lymphocytes

Fig. 5

a The patient presented with itchy subcutaneous swelling with no epidermal changes on the outer side of both upper arms. b Ultrasound examination revealed hypoechoic hypodermal nodules surrounded by a diffuse echoic subcutaneous tissue area. c Elastography showed mostly stiff tissues, with focal areas where stiffness was increased corresponding to the hypoechoic nodules. d Color-Doppler demonstrated increased peripheral vascularization