Relevant pelvic pathology is periodically encountered in the intensive care unit (ICU) setting and is amenable to bedside ultrasound evaluation. The pelvic pathology of interest in point of care ultrasonography may be split into three general categories. The first is a source of blood loss and will most typically include ectopic pregnancy, hemorrhagic cyst, or bleeding mass. The second is a source of infection and is most likely to include pelvic inflammatory disease (PID), tuboovarian abscess (TOA), retained products, and endometritis. The third is a source of pain apart from the first two categories, including ovarian cysts, masses, and ovarian torsion.
Sonographic pelvic anatomy can be challenging and depending on the ultrasound technique, anatomical relationships may appear confusing. The uterus, a pear-shaped muscular organ typically measuring 6–8 cm in length and 4 cm in width, is bordered anteriorly by the bladder and posteriorly by the rectum. The uterus is comprised of the fundus, body, and cervix where it narrows and protrudes into the vagina (Figure 22-1). The fallopian tubes exit the uterus on either side of the uterine fundus at the level of the cornua. The anterior cul-de-sac is a potential space between the uterus and bladder while the posterior cul-de-sac (Pouch of Douglas) is between the uterus and rectum. With the patient supine the Pouch of Douglas is the most dependent part of the pelvis and is typically the first area to collect fluid, such as blood or pus. The fallopian tubes extend laterally from the cornua in the broad ligament. An ovary attaches to the broad ligament posteriorly on each side. The iliac artery and vein run posterior and lateral to the ovaries and the two are a major landmark sonographically.
Ultrasound Examination: Transabdominal
The pelvic ultrasound examination is split into two distinct types that are not mutually exclusive and one may lead to the other depending on the pathology discovered. The easiest is the transabdominal (TAS) pelvic ultrasound examination. It is typically performed utilizing a curved linear array with a typical frequency range of 5–2.5 MHz. The broad field of view afforded by this type of transducer is ideal for surveying the pelvis. In general, the TAS pelvic ultrasound examination requires a full bladder. In the case of many ICU patients, this simply means clamping the urinary catheter. An alternative is to fill the bladder with either sterile saline. The ideal volume, which allows the bladder to act as an optimum acoustic window will vary from patient to patient. Approximately 250 mm will be ample in most cases and it is possible to overfill the bladder and actually move organs of interest farther away from the transducer. Similar to the pelvic portion of the fast assessments of surgical trauma (FAST) examination, the transducer is in two standard orientations. The transverse is with the marker oriented to the patient’s right hip and the longitudinal with the probe indicator pointed to the patient’s head. It is critical to scan through the bladder to best image pelvic organs in the TAS approach. Pelvic organs, like most others, should be scanned in two orthogonal planes. The classic image of a distended bladder in long axis is a triangular anechoic structure. In the transverse view the bladder will typically appear rectangular in shape (Figure 22-2). The TAS examination gives limited views of the ovaries and fallopian tubes in most patients. The fallopian tubes are rarely seen on TAS unless filled with fluid. Even then it may be difficult to differentiate them from other fluid collections without using an endovaginal (EV) approach. In many cases of complicated or subtle pathologic findings, both TAS and EV scanning will be required.
The left image shows a longitudinal cut through the bladder, uterus, and cervix. The bladder is triangular in appearance. Fluid can collect posterior to the uterus, near the cervix, or anterior to the fundus. The right image shows a transverse cut through the full bladder. The uterus (U) is shown in cross-section just below the rectangular bladder. The left ovary (LOV) is seen to the right of the uterus.
Ultrasound Examination: EV
The EV ultrasound approach is generally preferred for structures within the true pelvis. The ovaries are visualized with great detail, pregnancy can be seen at a much earlier date and ectopic pregnancies can be identified with much greater accuracy than with TAS.1 EV ultrasound is still typically described as an examination to perform after TAS. However, in clinical practice, the EV is often performed without a preceding TAS examination. The EV ultrasound examination requires an endocavity probe. These are typically microconvex and tend to range from 8 to 4 MHz, with some variation. Color or power Doppler is critical for this type of transducer in order to differentiate blood flowing in vessels from other types of fluid. The endocavity transducer is encased in a nonsterile sheath, such as a condom. Condoms with receptacle tips tend to trap air and are best avoided. The middle finger of a glove can be used as well. Hospital endocavity transducer decontamination policies and techniques should be strictly adhered to.
Prior to insertion into a sheath, the probe tip is covered with ultrasound gel. Once the sheath is slipped over the probe, the tip should be stretched tight and all air bubbles smoothed out with a finger. Additional gel is used on top of the sheath over the transducer scanning surface. Unlike the TAS approach, the EV approach requires an empty bladder. Once dressed properly, the probe is ready to insert into the vaginal vault. In modern society it is best to perform the examination in the constant presence of a chaperone, traditionally a female one. This will avoid potential questions that may be difficult to defend against if no chaperone was present. Typically, the probe is inserted too far by beginners and does not need to go beyond the anterior fornix. There are two general imaging planes in EV ultrasound. They are a coronal plane and a longitudinal plane. It may be helpful for beginners to imagine the patient standing on her head as they view the ultrasound machine screen. The anatomy will now make more sense, even though the orientation will take some time to adjust to.
With the probe indicator pointing toward the ceiling, the empty bladder, long axis of the uterus, and posterior structures are seen (Figure 22-3). A full bladder will make the examination frustrating and has to be corrected. The probe is moved from side to side to obtain images from one adnexa to the other. In addition, the transducer can be angled up and down while the indicator remains pointed toward the ceiling and introduced slightly deeper or pulled back in the vaginal vault. The fundus, cervix of the uterus, and surrounding structures can be visualized with good detail using these movements. To obtain short-axis view or coronal, the transducer is rotated toward the adnexa of interest and moved up and down or side to side (Figure 22-4). In EV scanning it is critical to image in two orthogonal planes as structures of interest are periodically seen better in one plane than another. The ovaries are located lateral to the uterus and are almost invariably anteromedial to the internal iliac artery and vein. These vascular structures are relatively easy to find on the EV examination and are an excellent landmark (Figure 22-5). The fallopian tubes can be seen leaving the cornuate portions of the uterine fundus on either side and may often be tracked nearly to each ovary, Figure 22-6. The tubes are obvious when filled with fluid, but with modern equipment they are still easily seen in most patients.
An endovaginal probe is being held in the vaginal vault of an ultrasound phantom, with the transducer indicator pointed toward the ceiling. This orientation gives a long-axis view through the uterus similar to Figure 22-1.