How to Find the Clitoris (On MRI)

INTRODUCTION: Traditionally, clitoral anatomy has been understudied in the medical literature. However, it is of vital importance to gynecologic surgeons. This anatomy can be explored using cadaveric dissections or MRI. MRI has a distinct advantage in that it can be performed in the living patient, where clinical features are known. It is critical for gynecologic surgeons to understand clitoral anatomy on MRI, independent of radiologic interpretation, especially when operating on or near the anterior vulva. OBJECTIVE: The aim of this study is to describe basic principles for gynecologists to use in evaluating clitoral anatomy using MRI. METHODS: OBGYN physicians from several institutions and at different career stages aimed to identify the MRI sequences and imaging planes that best allow identification of the clitoris and vestibular bulbs. Some raters had previous experience identifying the structures on MRI, while others were new to this type of clitoral imaging. Each author was tasked with identifying and measuring different clitoral and vestibular bulb structures across different MRI sequences (Table 1) and noting their findings and differences. Findings were reviewed at weekly meetings and compiled to create a systematic approach to visualizing the clitoris and vestibular bulbs on MRI. RESULTS: Clitoral and vestibular bulb structures are most easily seen on proton density (PD) and fat saturation sequences. Studies need to extend sufficiently distal in the axial plane and anterior/posterior in the coronal sequences to visualize the entire clitoris. Because the clitoris and vestibular bulbs are small structures, slices of 1–2 mm are best for detailed visualization. The clitoral glans, body, and crura can be seen on both PD and fat saturation sequences; however, the high intensity of these structures on fat saturation can help clearly distinguish their borders (Figure 1). The vestibular bulbs are clearly seen in axial and coronal sequences where their relationships to the perineal membrane are seen. They appear low intensity on PD and are very high intensity on fat saturation sequences. Occasionally, surrounding structures, such as the urethra, can be difficult to clearly visualize on fat saturation sequences. Mid-sagittal images are excellent for visualizing the clitoral glans, body, and suspensory ligament. CONCLUSIONS: The ease of identifying clitoral and vestibular bulb structures varies greatly depending on the MRI sequence, slice thickness, and plane. Ensure that the study includes the entirety of the structures in question in both the axial and coronal planes. Depending on the clinical question, gynecologic surgeons should consider requesting both PD and fat saturation sequences when imaging these structures and obtaining 1- to 2-mm slices or 3D sequences. Having both sequences provides complementary detail when evaluating the clitoris and vestibular bulbs. We recommend that the gynecologist take the opportunity to routinely review clitoral anatomy in their MRI studies, regardless of whether this was the focus of the study, in order to train their eyes in identifying these important structures.