Adenomyosis is a benign, oestrogen-dependent condition, characterised by the invasion of endometrial tissue into the myometrium (1), resulting in the disruption of the junctional zone. Its main symptoms include pain, menorrhagia, metrorrhagia, dysmenorrhea, and dyspareunia (2). While the exact cause of adenomyosis is unknown, the prevailing theory is that the endometrial glands directly invade the myometrium (2).

Two main theories seek to explain its pathogenesis: the invagination theory and the metaplasia theory. The first is based on the tissue injury and repair hypothesis, which suggests that chronic uterine hyperperistalsis, of still uncertain origin, causes repetitive microtraumas in the myometrium, particularly in the junctional zone (JZ) (3). These traumas trigger local inflammation and increase oestrogen production, creating a feedback loop that amplifies hyperperistalsis. This process leads to the disruption of muscle fibres in the JZ, allowing the basal layer of the endometrium to invade the myometrium, where adenomyosis forms (3). 

On the other hand, the metaplasia theory proposes that adenomyosis may originate from the transformation of embryonic remnants of pluripotent Müllerian cells located in the JZ region (3). Alternatively, it is suggested that endometrial stem or progenitor cells undergo abnormal differentiation and migrate into the myometrium. This aberrant cellular behaviour results in the formation of ectopic glands and stroma within the JZ, which respond to the hormonal fluctuations characteristic of the menstrual cycle, contributing to the pathology (3).

Adenomyosis can be classified as either diffuse or focal, depending on its distribution within the myometrium (4). Diffuse adenomyosis is characterized by multiple foci scattered throughout the uterine myometrium, whereas focal adenomyosis presents as isolated nodules of hypertrophic myometrium containing ectopic endometrial tissue (4).

Transvaginal US is now considered the primary imaging modality for the diagnosis of adenomyosis (1, 2), therefore, radiologists should be familiar with its sono-graphic appearance. 

In our study, we used ultrasound equipment equipped with 3D reconstruction software, volumetric acquisition transducers (mechanical 2D transducers scanning the region of interest), mechanical 3D transducers, 3D matrix transducers, and an intracavitary transvaginal ultrasound volume probe (TVS) to acquire 3D data sets in five patients from our institution. Descriptors and classifications available in the literature were employed.