Axillary swelling after vaccine

An eight-year-old female, previously healthy, was examined by a pediatrician due to a left axillary swelling that persisted for four weeks. This mass was noticed two weeks after receiving the first dose of the anti-SARS-CoV-2 vaccine. The patient denied experiencing other symptoms, trauma or recent infections. During the physical examination, a firm oval mass measuring 5x5 cm was observed, with no signs of inflammation (Figure 1).
She underwent an analytical study without any peculiarities and an axillary ultrasound, revealing an oval mass with multiple indentations and hypoechoic elements. This pattern suggested an atypical adenopathy conglomerate in the context of a vaccine reaction. Consequently, she initiated treatment with a seven-day course of amoxicillin + clavulanic acid and ibuprofen.
On re-evaluation, there was no change observed in the mass. Consequently, the case was reviewed with Pediatric Oncology and a referral for consultation was made. A repeat axillary ultrasound revealed a heterogeneous formation with cystic foci and areas of vascularization, accompanied by rare foci of calcification (Figure 2). Subsequent Magnetic Resonance Imaging (MRI) confirmed the presence of a lesion consistent with low-flow vascular malformation within the teres minor muscle (Figure 3). The child underwent surgical excision and histology confirmed the diagnosis of intramuscular hemangioma (IMH).

Figure 1. Oval mass in left axile, with 5 x 5 cm.


Figure 2. Ultrasound images showing heterogeneous formation, with cystic foci (A) and areas of intralesional vascularization (B), with rare foci of calcification.


Figure 3. A) MRI Axial T1 imaging showing lesion, with lobulated contours, within left teres minor muscle, demonstrating intermediate signal; B) MRI Axial STIR viewing lesion with hypersignal, plus foci of hyposignal; C) MRI Axial imaging after contrast, showing heterogeneous impregnation of contrast product in the lesion.


What is intramuscular hemangioma?