Dr Paula Woodward, Professor in Radiology, Univ of Utah, USA in an interaction with M Neelam Kachhap, speaks about the evolution of diagnostic radiology in India and what future changes can be observed in foetal imaging
How has diagnostic radiology evolved and what difference do you see in the practice in the US as compared to India?
Ultrasound in general and foetal imaging specifically has changed dramatically. When I began we had B-mode images which we developed in the darkroom. Now there are sophisticated computer workstations where we view and reconstruct 3D images. Probes and software have ever improving resolution allowing us to view normal embryologic development (sonoembryology) in a way we never dreamed possible. Many anomalies, especially severe ones, can now be detected in the first trimester. High speed MRI sequences have also advanced the field of prenatal diagnosis. It is a wonderful adjunct to foetal imaging particularly for CNS malformations.
Since I have not had the opportunity to visit India before, I don’t think I can appropriately answer the second part of this question. I look forward to speaking with the course organisers and participants when I am there to learn about regional practices.
What are the challenges faced in imaging first trimester pregnancies?
There have been major changes in both terminology and treatment recommendations in first trimester pregnancies in the last few years. Both the Royal College of Obstetrics and Gynecology in the UK and the Society of Radiologists in Ultrasound in the US have adopted far more conservative guidelines for the diagnosis of a failed pregnancy. The same holds true for the diagnosis of ectopic pregnancy. The hCG used to be an important parameter in diagnosing an ectopic pregnancy. Now, a single measurement, regardless of its value, should not be used to determine management in a haemodynamically stable patient. It has been a major paradigm shift in diagnosis and patient management, with the focus being on not intervening on a potentially viable pregnancy.
What are the complications of twinning?
Determining chorionicity and amnionicity is critical for managing a twin pregnancy. Twins that share a placenta (monochorionic) are at far greater risk of complications than those with separate placentas (dichorionic). It is important to monitor monochorionic twins for the development of twin-twin transfusion syndrome, the result of a placental artery-to-vein anastomosis. The donor (pump) twin becomes oligemic resulting in oligohydramnios, while the recipient twin develops polyhydramnios. Specific staging criteria are established to identify which cases would benefit from intervention with laser coagulation of the anastomotic vessels. Left untreated there is a 70-90 per cent mortality rate, with the donor dying first in 2/3 of cases.
Another more rare complication of monochorionic twins is twin reversed arterial perfusion (TRAP), the result of an artery-to-artery anastomosis. Deoxygenated blood from the donor flows into the recipient via the umbilical artery (reversed from normal flow which is away from the foetus). The recipient is often severely hydropic and very dysmorphic in appearance. This is the result of preferential flow to the lower extremities. The upper portion of the foetus is under developed and there is often no heart, leading to the term acardiac twin.
If twins are monoamniotic (share a single sac without an intervening membrane) they are at risk for cord entanglement and in utero demise.
What are the challenges in imaging foetal tumours?
Foetal tumours, while uncommon, pose a very unique circumstance in the care of an obstetric patient and create significant medical and ethical dilemmas. Although the diagnosis of any foetal anomaly is a devastating event for a family, the presence of a foetal tumour carries with it additional diagnostic and therapeutic challenges. The prognosis is generally poor, although there are some notable exceptions. An understanding of the different tumour types and their biological behaviour is necessary for appropriate counseling and care of these patients. Accurate diagnosis has important implications for foetal, maternal and neonatal care.
The biologic behaviour of tumours in the foetus may differ dramatically when compared to the same tumour detected later in life. Teratomas are the dominant histologic type and comprise the majority of both extracranial and intracranial neoplasms. Although often histologically mature, they may prove lethal based on location and metabolic demands on the foetus. Large solid tumours may lead to cardiovascular compromise and hydrops fetalis. Extracranial teratomas are most commonly located in the sacrococcygeal area followed by the head and neck, chest, and retroperitoneum. Foetuses with intracranial tumours have a poor prognosis regardless of histologic type. There are, however, two notable exceptions: lipomas and choroid plexus papillomas both of which have a more favorable outcome. Neuroblastoma is the most common fetal malignancy. It may be either solid or cystic and is more often located on the right side. It typically has favourable biologic markers and stage at presentation. The prognosis for prenatally diagnosed cases is excellent. Other foetal neoplasms include soft tissue tumours (both benign and malignant), leukemia, mesoblastic nephroma of the kidney, and liver tumours (haemangioendothelioma, mesenchymal hamartoma and hepatoblastoma).
Could you talk about GI & GU anomalies and how best report on them?
Anomalies of the foetal gastrointestinal (GI) and genitourinary (GU) tracts are a complex group of anomalies, many of which are incorrectly diagnosed. It is imperative that when diagnosing and reporting on these anomalies that ancillary features be described to come to the most specific diagnosis possible.
Urinary tract malformations are the most common cause of a cystic abdominal mass in a fetus. When dealing with a cystic renal mass it is important to determine if the cysts are non-communicating, as in a multicystic dysplastic kidney, or if they communicate centrally, in which case they aren’t cysts at all but are dilated calyces. If only the upper pole of the kidney is involved think about a possible duplicated system and the bladder should be carefully interrogated for a ureterocele.
Gender matters as a dilated bladder in a male foetus is most likely posterior urethral valves; however, prune belly can have a similar appearance so ancillary findings such as undescended testes and flaccid musculature should be evaluated for and reported. Other cystic malformations such as an ovarian cyst and cloacal malformation are only seen in female foetuses.
GI tract dilatation is generally from atresia but it is important to report on any complications. Always look for intraperitoneal calcifications or meconium pseudocyst formation which would indicate perforation. A choledochal cyst is an uncommon cause of a cystic mass but can be confidently diagnosed if bile ducts can be shown to be entering into it.
While cystic abdominal masses are a diverse group of disorders analysing and reporting on specific features, using the age of the foetus at presentation, and foetal gender can be combined making a specific diagnosis possible.