Introduction

Diagnostic imaging has an important role in diagnosis, treatment planning and follow-up of gynaecological malignancies. Gynaecological imaging modalities include ultrasound (US), magnetic resonance imaging (MRI), computerised tomography (CT) and positron emission tomography (PET). These modalities have their own inherent strengths and weaknesses. By understanding these factors, the most appropriate investigation can be performed to provide the most useful information in different clinical scenarios.

Ultrasound

US has a pivotal role in gynaecological imaging as it is widely available and a relatively cheap imaging investigation. US images are created with high-frequency sound waves and therefore can be safely utilised in all patients. US is the imaging modality of choice in the initial investigation of patients presenting with abnormal vaginal bleeding, pelvic pain or suspected pelvic mass. Ideally US should be performed using both transabdominal and transvaginal methods, to ensure that all pathologies are detected and accurately characterised. Transabdominal US (TAUS) is performed with a 3.5–5.0 MHz transducer in patients with a full bladder, which serves to displace bowel loops (and therefore gas) from the pelvis and provides a sonographic window for clearer images. TAUS is particularly useful in patients with a bulky fibroid uterus or large volume adnexal masses that may extend from the pelvis into the abdominal cavity. TAUS also enables assessment of the upper abdomen for the presence of associated pathology such as ascites or hydronephrosis.

Transvaginal US (TVUS) is performed once the patient has emptied her bladder, which allows the pelvic organs to be closely apposed to the US probe. The smaller depth of field means that a higher frequency probe can be used (typically 5–7.5 MHz), which provides higher-resolution images. The high-resolution imaging of TVUS allows the assessment of endometrial thickness in patients with postmenopausal bleeding and characterisation of adnexal masses, with approximately 20% remaining indeterminate. TVUS is able to detect small papillary lesions and mural nodules within complex ovarian cysts. Colour and power Doppler are used to identify soft tissue vascularity.

US imaging has limitations in patients with a large body mass index (BMI), as it can be difficult to produce diagnostic images due to the increased distance between the probe and pelvic organs. Images can be obscured by bowel gas or by a poorly filled bladder in TAUS. These differences can lead to inter-observer variability.