The fallopian tubes project out from each side of the body of the uterus and form the passages through which the egg is conducted from the ovary into the uterus. The fallopian tubes are about 10 cms long and the outer end of each tube is funnel shaped, ending in long fringes called fimbriae. The fimbriae catch the mature egg and channel it down into the fallopian tube when released by the ovary .
The tube itself is a muscular highly movable structure capable of highly coordinated movement. The egg and sperm meet in the outer half of the fallopian tube, called the ampulla. Fertilization occurs here, after which the embryo continues down the tube toward the uterus. The uterine end of the tube, called the isthmus, acts like a sphincter, and prevents the embryo from being released into the uterus until just the right time for implantation, which is about 4 to 7 days after ovulation.
The tube is much more complex than a simple pipe, and the lining of the tube is folded and lined with microscopic hair like projections called cilia which push the egg and embryo along the tube. The tubal lining also produces a fluid that nourishes the egg and embryo during their journey in the tube.
An abnormal HSG may show a problem in the uterine cavity - and this appears as a gap or filling defect. However, the commonest problems on HSG appear in the tubes. If the tubes are blocked at the cornual end (at the uterotubal junction), then no dye enters the tubes and they cannot be seen at all. If the block is at the fimbrial end then the tubes fill up; but the dye does not spill out into the abdominal cavity and the end of the tubes are often swollen up.
Sometimes, like any other medical test, the HSG may provide erroneous results. For example, the cornu of the uterus may go into spasm, as a result of which the dye may not enter the tubes at all. This may be interpreted as a tubal block, whereas in reality the tubes are open. Also, if a hydrosalpinx is very thin and if the dye is injected under pressure, the dye may appear to spill into the abdomen through a tear in the wall of the hydrosalpinx - suggesting tubal patency when really the tubes are closed.
While the HSG is usually very reliable for determining whether or not the tubes are open, it provides little information on structures outside the tube which could nevertheless impair tubal function - such as peritubal adhesions. If the spill is "loculated",(i.e. it collects in small puddles), the presence of adhesions can be suspected, but not confirmed.
An HSG can be painful - and when the dye is injected into the uterine cavity, most women will experience a considerable amount of pain. You should be prepared for this - and taking a pain-killer prior to the procedure will help to reduce the pain.
An HSG can be technically difficult for some women (especially if the cervix is too small or too tight) - and it is better if a gynecologist is present at the time of the HSG to assist the radiologist if needed. Many gynecologists will do the HSG themselves.
The major risk of an HSG is that of spreading an unrecognized infection from the cervix up into the tubes. This is uncommon, but in order to reduce the risk, many doctors advise antibiotic coverage during the procedure.
If the HSG shows that the tubes are closed, then it may be advisable to repeat the HSG; and also to do a laparoscopy to confirm this diagnosis.
The trouble with both HSG and laparoscopy is that they only provide information as to whether or not the tube is open or closed. While a closed tube will never work, they do not provide any information on how well an apparently open tube works. Remember, that just because a tube is patent does not necessarily mean that it works!
Fig 3. Laparoscopy shows a large hydrosalpinx on the right side
Another limitation is that they will rarely provide any information as to why the tubes are blocked. Occasionally, however, this can be suspected by other signs (for example, by seeing the tubercles diagnostic of TB in the abdomen during laparoscopy).
Using an image intensifier, and techniques borrowed from coronary angioplasty, the radiologists can now insert special catheters under fluoroscopic guidance into each of the tubes. This is called selective salpingography; and allows much better visualization of each tube. It also allows the radiologist to treat cornual blocks which are due to mucus plugs by tubal cannulation.
Under ultrasound guidance, with Doppler facilities if available, the gynecologist can inject fluid into the tubes through the cervix and see the flow of the fluid into the tubes and abdomen on the ultrasound screen. This is a simple bedside test which a gynecologist can do to judge if the tubes are normal - and can be reassuring if positive.
At the time of laparoscopy, the doctor can insert a fine telescope into the fallopian tube through its fimbrial end, to inspect the inner lining of the tube, to judge whether or not it is healthy.
Falloposcopy is a recent advance, pioneered by Dr Kerin of USA. In this method, a very fine flexible fiberoptic tube is guided through the cervix and uterus into each fallopian tube, thus allowing the doctor to actually visualize the inner lining of the entire length of the fallopian tube - something which was never possible so far. This can provide useful information about the extent of tubal damage, and the possibility for successful repair.