MAGNETIC RESONANCE IMAGING TECHNIQUES IN THE PELVIS

Benign and Suspicious Ovarian Masses-MR Imaging Criteria for Characterization: Pictorial Review

Ovarian masses present a special diagnostic challenge when imaging findings cannot be categorized into benign or malignant pathology. Ultrasonography (US), Computed Tomography (CT), and Magnetic Resonance Imaging (MRI) are currently used to evaluate ovarian tumors. US is the first-line imaging investigation for suspected adnexal masses. Color Doppler US helps the diagnosis identifying vascularized components within the mass. CT is commonly performed in preoperative evaluation of a suspected ovarian malignancy, but it exposes patients to radiation. When US findings are nondiagnostic or equivocal, MRI can be a valuable problem solving tool, useful to give also surgical planning information. MRI is well known to provide accurate information about hemorrhage, fat, and collagen. It is able to identify different types of tissue contained in pelvic masses, distinguishing benign from malignant ovarian tumors. The knowledge of clinical syndromes and MRI features of these conditions is crucial in establishing an accurate diagnosis and determining appropriate treatment. The purpose of this paper is to illustrate MRI findings in neoplastic and non-neoplastic ovarian masses, which were assessed into three groups: cystic, solid, and solid/cystic lesions. MRI criteria for the correct diagnosis and characteristics for differentiating benign from malignant conditions are shown in this paper.

MR Imaging of the Female Pelvis at 3T

The recent development of the transmit-receive body coil and the dedicated torso phased-array radio frequency receive coil for 3.0T MR imaging systems has promoted a move toward higher-field, whole-body MR imaging, including pelvic MR imaging. The female pelvis is an anatomic area that may benefit particularly from the advantages of high-field systems. In this article, the authors present their initial experience with the optimization of sequences for MR imaging of the female pelvis at 3.0T, and include a short description of parallel imaging. They compare some of the physical properties of 1.5T and 3.0T, discuss some of the challenges during sequence optimization for the female pelvis at 3.0T, and give examples of female pelvic abnormalities.

Pelvic anatomy and MRI

An in-depth knowledge of the anatomy of the pelvis and pelvic sidewall is necessary before a gynaecologist can even contemplate making an initial examination and start management in cases of pelvic pathology or malignancy. This chapter provides basic information on gross pelvic anatomy structures that are of clinical relevance and discusses their correlation with medical imaging, especially magnetic resonance imaging (MRI). MRI is an ideal non-invasive technique in the assessment of normal anatomy and tissue characterization of pelvic pathology. The excellent soft-tissue contrast and the ability to direct multiplanar imaging and to demonstrate blood vessels without the use of intravenous contrast make MRI superior to other imaging modalities in the evaluation of pelvic abnormalities. The anatomical relation of the visceral organs, the differential zonal anatomy of the corpus uteri and the cyclical endometrial changes during the menstrual cycle are well depicted with MRI.

Imaging evaluation of ovarian masses

Adnexal masses present a special diagnostic challenge, in part because benign adnexal masses greatly outnumber malignant ones. Determination of a degree of suspicion for malignancy is critical and is based largely on imaging appearance. Endovaginal ultrasonography (US) is the most practical modality for assessment of ovarian tumors because it is readily available and has a high negative predictive value. Morphologic analysis of adnexal masses is accurate for identifying masses as either low risk or high risk. The most important morphologic features are non-fatty solid (vascularized) tissue, thick septations, and papillary projections. Color Doppler US helps identify solid, vascularized components in a mass. Spectral Doppler waveform characteristics (eg, resistive index, pulsatility index) correlate well with malignancy but generally add little information to morphologic considerations. Computed tomography can help assess the extent of disease in patients before and after primary cytoreductive surgery. Magnetic resonance (MR) imaging is better reserved for problem solving when US findings are nondiagnostic or equivocal because, although it is more accurate for diagnosis, it is also more expensive. The signal intensity characteristics of ovarian masses make possible a systematic approach to diagnosis. Mature cystic teratomas, cysts, endometriomas, leiomyomas, fibromas, and other lesions can be accurately diagnosed on the basis of T1-weighted, T2-weighted, and fat-saturated T1-weighted MR imaging findings.

Tissue characterization in the female pelvis by means of MR imaging

Pelvic imaging techniques such as computed tomography and ultrasonography provide a limited capability for tissue characterization. Fat, fluid, and calcification, for example, can be identified on the basis of parameters such as x-ray attenuation, echogenicity, and sound attenuation. Because of the many tissue parameters, such as T1, T2, magnetic susceptibility, and chemical shift, that contribute to signal intensity, magnetic resonance (MR) imaging may afford an ability to identify a wider array of specific tissues. The purpose of this article is to review the ability of MR imaging to help identify various types of soft tissue and to provide an approach to interpretation of MR images of the female pelvis through tissue characterization. Lipid, fluid, hemorrhage, smooth muscle, fibrosis, solid malignant tissue, and hydrated soft tissue (including edema, mucin, and myxomatous tissue) have typical MR imaging properties, and their presence in a mass can often be established on MR images. Consideration of the tissue composition of various pathologic processes in the pelvis can result in more systematic approaches to image interpretation and thus narrow the differential diagnosis.