Point-of-care pelvic ultrasound

Published on 22/03/2015 by admin

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Point-of-care pelvic ultrasound

LORI STOLZ and SRIKAR ADHIKARI

Overview

This chapter illustrates the basic features of pelvic ultrasound by outlining the exploration of the female genital system, concluding thus the holistic approach (HOLA) ultrasound concept of the abdominal examination (see Chapters 1 and 44). Clinician-performed point-of-care pelvic ultrasound is an integral skill in a growing number of medical subspecialties. History and physical examination are not always reliable in the evaluation of possible pelvic pathology, especially in the critically ill patient. The ability to diagnose life-threatening conditions at the bedside can decrease time to diagnosis. Ultrasonography is the preferred imaging modality for female pelvic anatomy in both the nonpregnant and pregnant patient. The accuracy of clinician-performed bedside ultrasound in identifying pelvic pathology has been well established.

Indications

Abdominal pain, pelvic pain, and vaginal bleeding are common complaints for which pelvic ultrasound is used. Although less common, pelvic ultrasound may also be indicated for syncope, dizziness, abdominal or pelvic mass on physical examination, trauma, fever, and hemodynamic instability. In the setting of pregnancy, the first and foremost use of pelvic ultrasound is in the diagnosis of an intrauterine pregnancy (IUP). Once an IUP has been established, ultrasonography can be further used to document gestational age, fetal heart rate, subchorionic hemorrhage, abnormal pregnancies, pregnancy loss, or to follow normal pregnancy. For the nonpregnant, critically ill patient, other pertinent applications include the evaluation of life-threatening ovarian pathology, such as ovarian torsion, ovarian cyst rupture with associated hemorrhage, and tubo-ovarian abscess. In any female who is hypotensive, septic, febrile, or suffering from severe abdominal pain, pelvic ultrasound is an extremely useful tool to direct appropriate treatment.¹^,²

Technique and normal anatomy

Imaging of the pelvic organs is assisted by the use of both transabdominal sonography (TAS) and transvaginal sonography (TVS). Each technique has its own advantages in the assessment of pelvic organs. A transabdominal approach gives the examiner spatial orientation of the pelvis and defines the relationship of the uterus with adjacent pelvic and abdominal structures. It is also helpful to delineate large masses, free fluid, and other pathology extending outside of the true pelvis. A transvaginal approach is useful because of probe proximity to the pelvic organs and the higher frequency resulting in images with superior resolution. This approach provides more anatomic detail of pelvic structures, allowing early identification of intrauterine contents and adnexal abnormalities. In addition, the probe can be used to detect the mobility of the pelvic organs. This can reveal adhesions and highlight pelvic pathology. These two modalities are complimentary, and in the undifferentiated patient, we recommend using both approaches.1–4

Transabdominal technique

For TAS, scanning starts in the suprapubic area, using a low-frequency curvilinear transducer. The examination is best performed with a full bladder, although an overly distended bladder will decrease image quality. The bladder acts as an acoustic window and also displaces bowel loops from the pelvis for better imaging.1–4 With the indicator directed cephalad, sagittal images can be obtained by sweeping the transducer slowly from right to left. Transverse images can be obtained with the indicator to the patient’s right, by convention. By gently sweeping the transducer caudad and cephalad, all organs can be imaged in all three dimensions. The examiner should first start with an assessment of the uterus in both the sagittal and transverse planes. The position of the uterus, whether it is anteverted or retroverted, should be noted. Obesity and retroverted position can present challenges to the sonographer. The various portions of the uterus are then identified, namely, the cervix, body, fundus, and endometrial stripe. Sonographically, the normal uterus exhibits a low-gray homogenous texture. The endometrial stripe is typically seen as an echogenic line in the middle of the uterus (Figures 43 E-1 and 43 E-2). The appearance of uterine endometrium changes as the thickness of the endometrium changes with different phases of menstrual cycle. The cervix has similar sonographic appearance to that of the rest of the uterus. The thin linear hyperechoic vaginal canal is visualized between the anechoic urinary bladder (anterior) and the echogenic rectum (posterior). The cul-de-sac should be evaluated for free fluid or hematoma or mass, both in long and transverse planes. Next, the operator moves the transducer to the right or left lower quadrants to identify the adnexa. The identification of the ovaries is aided by identifying the iliac vessels, which define the borders of the pelvis. The ovaries are often adjacent to them. Ovaries are identified by their “chocolate chip cookie” appearance of hypoechoic follicles within the ovary. Again, they should be imaged in two planes, sagittal and transverse. Ovarian size can be evaluated by measuring the ovary’s dimensions in three planes. Normal ovarian measurements are approximately 5.1 ± 3.1 cm³ in the preovulation period, 3.2 ± 1.7 cm³ in the postovulation period, and 1.3 ± 0.6 cm³ in postmenopausal women. Ovaries may not always be seen on TAS but are visualized 65% to 99% of the time when performed in the radiology suite.³^,⁴

Figure 43 E-1 Longitudinal view of a nonpregnant uterus by transabdominal sonography (TAS).

Figure 43 E-2 Transverse view of a nonpregnant uterus by transabdominal sonography (TAS).

Transvaginal technique

For TVS, consent should be obtained and the procedure explained, if at all possible. A chaperone should also be present. The patient should be placed in lithotomy position, and the bladder should be decompressed because a distended bladder can distort the normal pelvic anatomy and push the uterus posteriorly.³^,⁴ The transducer should be prepared with an appropriate cover, with lubricating gel inside and outside of the cover. The endocavitary transducer is directed to different points of interest by using the midpoint on the probe as a fulcrum. To image anteriorly on the body, the transducer handle should be moved posteriorly, thus bringing the imaging of the probe anteriorly. This principle is one of the frequent missteps of novice sonographers but can be easily learned and mastered. Just as in TAS, assessment begins with the uterus imaged in two planes. With the indicator facing the ceiling, the sagittal images are obtained, and with the indicator pointed to the right side of the patient, the coronal plane images are obtained. The uterine contents should be screened thoroughly, and the posterior cul-de-sac should be evaluated at the level of the fundus, body, and cervix (Figures 43 E-3 to 43 E-5). The free fluid in the posterior cul-de-sac can be quantified into small (free fluid seen < 1⁄3 of the way up the posterior wall of the uterus), medium (free fluid seen 2⁄3 of the way up the posterior wall of the uterus), and large (free fluid seen > 2⁄3 tracking along the posterior wall of the uterus). The transducer is then angled rightward or leftward to visualize the adnexa. Again, the proximity of the ovaries to the iliac vessels can be used to locate them, and each structure should be imaged in two planes, coronal and sagittal.³^,⁴ Typically, the ovaries are found lateral to the uterus, medial and anterior to the iliac vessels (Figure 43 E-6).