Question

Discuss placental evaluation by ultrasound. Discuss the imaging findings in placenta accreta spectrum disorders. [5+5]

Hint:

Ultrasound is the key tool for diagnosing placenta accreta spectrum. Key signs include loss of the hypoechoic zone between the placenta and myometrium, placental lacunae, and abnormal blood flow patterns on Doppler ultrasound.

Answer 1

Step 1: Placental Evaluation by Ultrasound.
Placental evaluation by ultrasound is essential during pregnancy to assess the position, structure, and any abnormalities of the placenta. Ultrasound is the primary imaging tool used in the antenatal period for placental assessment because it is non-invasive, safe, and provides real-time imaging. (1) Indications for Placental Ultrasound: - Placenta previa: When the placenta is abnormally located near or covering the cervical os, leading to a risk of bleeding. - Placental abruption: In cases of premature separation of the placenta from the uterine wall. - Placenta accreta, increta, percreta: To assess placental invasion into the uterine wall. - Intrauterine growth restriction (IUGR): To assess placental blood flow and structure. - Multiple pregnancies: To assess placental position and function in twin or triplet pregnancies. (2) Techniques for Placental Ultrasound: - Transabdominal ultrasound: The most common method, useful for routine assessments of placental location and morphology. - Transvaginal ultrasound: Provides better resolution for assessing placental location, especially in cases of placenta previa or low-lying placenta. It is also valuable in identifying placenta accreta. (3) Ultrasound Findings in Normal Pregnancy: - Placental location: The placenta is typically attached to the upper posterior or anterior uterine wall and should not extend over the cervix. The placental thickness is generally 2-4 cm. - Placental grade: Grading the placenta from Grade 0 (smooth, homogeneous) to Grade 3 (with calcifications, lobulations, and cystic spaces) depending on gestational age. - Placental blood flow: Doppler ultrasound may be used to assess blood flow in the umbilical artery and uterine arteries, helping to evaluate placental function and fetal well-being.
Step 2: Imaging Findings in Placenta Accreta Spectrum Disorders.
Placenta accreta spectrum (PAS) refers to a group of conditions where the placenta abnormally attaches to the uterine wall and invades deeper layers. This spectrum includes placenta accreta, placenta increta, and placenta percreta. Early diagnosis of PAS is critical to manage complications such as massive bleeding and the need for hysterectomy. Ultrasound imaging is the key diagnostic tool for PAS. (1) Placenta Accreta: - Definition: The placenta adheres to the uterine wall but does not invade deeply into the myometrium. - Ultrasound Findings: - Loss of normal hypoechoic zone between the placenta and myometrium. - Placental lacunae or vascular spaces that appear as hypoechoic areas within the placenta. - Irregularities or thinning of the uterine wall may be visible. - Increased blood flow in the placental bed as seen on Doppler ultrasound.
- The myometrial thickness may appear decreased at the site of placenta accreta. (2) Placenta Increta: - Definition: The placenta invades into the myometrium (muscular layer of the uterus). - Ultrasound Findings: - Deep placental lacunae with irregular vascular spaces that may extend into the myometrium. - Thinning or absence of the myometrium in the area of invasion. - Color Doppler may show high-velocity blood flow around the invading vessels, which could suggest the presence of an abnormal placenta. - Loss of the normal interface between the placenta and the uterus.
(3) Placenta Percreta: - Definition: The placenta perforates through the entire myometrium and may extend into the serosa or other surrounding structures such as the bladder or rectum. - Ultrasound Findings: - Full-thickness invasion of the placenta through the uterine wall. - Absence of myometrium between the placenta and the surrounding structures (e.g., bladder). - Vascular spaces or lacunae that penetrate the myometrium and may even be seen extending outside the uterine wall. - Color Doppler may show abnormal blood vessels that appear to cross into the bladder or other structures.
- The presence of placental bulging or bladder wall involvement may suggest percreta.
(4) Differential Diagnosis: - PAS must be distinguished from other conditions that can cause similar ultrasound findings, such as placenta previa or fibroids, which can have overlapping features like vascularity or lacunae. A careful assessment of placental location, myometrial thickness, and Doppler patterns is necessary for accurate diagnosis.