Female patient, aged 23 years, non-smoker, with no relevant medical or surgical history or known drug allergies. She came to the clinic because of an increase in the volume of the lower vestibular gum, adjacent to the left mental orifice, of 2 months' evolution, with active growth. It was not related to traumatic causes. Clinical examination revealed a nodule 0.5 cm in diameter, of fibroelastic consistency on palpation, similar in colour to normal mucosa, partially adherent to deep planes and painless. On radiological examination, no particularities were observed in the area of the lesion.

Under local anaesthesia, an excisional biopsy of the lesion was performed. Pathological examination revealed a proliferation of spindle cells arranged in short swirling fascicles, with abundant vascular structures of myxomatous appearance, isolated collagen deposits and foci of lymphocytic infiltrate with extravasated red blood cells. Immunohistochemical studies were also performed and were positive for vimentin and smooth muscle actin and negative for alk-protein 1, beta catenin, CD 34, desmin, S-100. Ki67 expression was 5-6% of labelled nuclei. This picture corresponds to the diagnosis of nodular fasciitis. The patient was followed up for 18 months and no recurrence was observed.