The HSG procedure — hysterosalpingography — is one of the oldest tests in radiology and still one of the most consequential. In under twenty minutes, a few millilitres of contrast answer questions that months of blood tests cannot: is the uterine cavity shaped for implantation, and are the fallopian tubes open? For the one in six couples facing infertility, this single study often redirects the entire treatment pathway.

Yet the quality of an HSG procedure is decided less by the machine than by the hand. Inject too fast and the patient experiences severe cramping; the tubes spasm and mimic blockage. Use cold, uncontrolled instillation and the cavity distorts under pressure. Choose the wrong contrast and you forfeit a proven fertility benefit. This module teaches the test the way I teach it to registrars and sonographers: gently, systematically, and with the patient in the room as a partner, not a passenger.

Seven essentials follow — anatomy, contrast, technique, interpretation, and the human factors that make the difference between a study a patient endures and one she would recommend.

The test itself is a century old in concept and modern in execution: digital subtraction imaging, low-dose pulsed fluoroscopy, and soft disposable catheters have transformed it from a feared rite of passage into a genuinely tolerable — sometimes therapeutic — outpatient procedure. What has not changed is the operator's responsibility. Every image begins as a decision made at the bedside: how fast to inject, when to stop, what to tell the frightened patient holding your hand. That is why this module treats the HSG procedure as a complete clinical skill rather than a radiographic recipe.

1. Anatomy review

Every interpretation starts with a mental template of normal. Contrast enters through the cervix and fills the endometrial cavity — classically a triangle, or an inverted trapezoid in nulliparous women — with smooth, sharp cornual angles where the tubes arise. Each tube runs approximately 10–12 cm through four named segments: interstitial (within the uterine wall), isthmus (narrow), ampulla (wide and tortuous), and the fimbrial end opening into the peritoneal cavity.

The endpoint of a normal HSG procedure is free spill: contrast curling from the fimbrial ends into the peritoneal cavity, outlining bowel loops without loculation. Delayed spill, loculated collections, or complete absence of spill each carry specific meaning — and each is only credible when the injection was gentle enough to avoid the false occlusion of tubal spasm. Radiologist-oriented reviews of tubal patency imaging emphasize this physiological caveat above all others⁷.

The anomalies that change management

Two anomalies deserve particular respect because they look similar on a single film but diverge completely in management. A septate uterus has a normal external fundal contour with an internal division — associated with recurrent pregnancy loss and corrected by hysteroscopic resection. A bicornuate uterus has an external fundal cleft greater than a centimetre — a fusion defect managed very differently, and often not operated at all. HSG alone cannot reliably separate them; the external contour question belongs to ultrasound or MRI. The same discipline applies to arcuate variants, which most authorities now consider normal, and to the narrow, T-shaped cavity of DES exposure, which shortens functional cavity volume. Recording what the study can and cannot resolve is part of a professional HSG procedure report — overcalling a septum from a pressured film has led to unnecessary surgery.

What can masquerade as pathology

• Tubal spasm: forceful injection triggers transient cornual spasm that mimics proximal occlusion; slow instillation and a delayed film settle the question.
• Uterine contractions: normal myometrial contractions during filling distort the cavity into transient, meaningless shapes.
• Air bubbles: tiny filling defects that move between films — the commonest mimic of polyps.
• Overdistension: excessive pressure elongates and deforms the cavity, hiding a septum or exaggerating a subtle anomaly.

2. Contrast agents: oil vs water

The contrast decision is no longer cosmetic. The H2Oil randomized trial, published in the New England Journal of Medicine, allocated infertile women to oil-based (ethiodized poppy-seed oil — Lipiodol) versus water-based contrast at HSG and found significantly higher ongoing pregnancy and live-birth rates in the oil group¹. Meta-analyses, long-term follow-up, and a large multicentre Chinese trial have since confirmed and extended the signal^2,3,4,6.

The mechanism appears to be a therapeutic flushing effect: oil droplets dislodge debris, mucus plugs, and peritubal adhesions, and the lipid itself may modulate the peritoneal environment. Whatever the precise pathway, the practical conclusion for the modern HSG procedure is that contrast choice is a clinical decision with fertility consequences, not a stock-room accident.

Choosing and handling

• Oil-based (Lipiodol): radiopaque, dense, slow to clear; best image quality; carries the fertility benefit; use warmed to body temperature and instill gently.
• Water-based: clears quickly, lower viscosity for cervical stenosis; reserve for specific indications or patient factors.
• Volume discipline: typically 5–15 mL; stop when diagnostic images are obtained — more volume buys no more information and costs comfort¹².
• Safety screen: active pelvic infection and pregnancy remain absolute contraindications; adverse events are uncommon but real, and risk rises with technique¹³.

Adverse events are uncommon but must be screened for deliberately. Vasovagal reactions during or immediately after the procedure are the commonest event; pelvic infection occurs in roughly one to three percent, concentrated in women with prior pelvic inflammatory disease; and intravasation of contrast into myometrial or pelvic veins, usually a consequence of forceful injection, is self-limited in most cases but should be documented and the patient observed^13,23. Patient selection does most of the preventive work: exclude pregnancy, ask directly about infection history, and never schedule against an uncertain cycle day.

3. The SATMix HSG technique: gentle, controlled, complete

Technique is the strongest modifiable determinant of a successful HSG procedure. The goals are threefold: adequate distension for a diagnostic cavity view, tubal opacification without spasm, and an image series that answers the clinical question — at the minimum possible discomfort. Every habit below serves those goals.

The protocol

1. Timing: cycle days 7–12 — the endometrium is thin, the patient is not pregnant, and the study cannot disrupt an implantation window.
2. Preparation: negative pregnancy test, prophylactic analgesia offered routinely, and antibiotics for selected risk histories.
3. Catheter choice: a soft balloon catheter placed in the lower cavity or cervical canal reduces pain dramatically compared with rigid metal cannulae¹⁶.
4. Contrast handling: warm the oil to body temperature; load in oil-resistant components with smooth, low-resistance plungers.
5. Injection: slow, continuous, low-pressure instillation under fluoroscopy — watch the cavity first, then each tube, then spill.
6. Imaging: early cavity film, per-tube films, and a spill film; a delayed view when spill is equivocal.

The physics of gentleness deserve respect. Lipiodol is viscous; a sticky plunger at the moment of maximum patient anxiety produces the jerky, over-pressure injection that causes both spasm and severe cramp. Hardware matters here: the SATMix HSG set pairs oil-resistant syringes — validated for 24-hour contact — with a low-resistance delivery pathway, so the operator's hand pressure converts into smooth flow rather than surges.

Dose discipline

The HSG procedure is performed on young women, sometimes repeatedly across a fertility journey, and dose discipline is therefore a clinical quality metric, not an administrative one. Collimate tightly to the pelvis, use pulsed fluoroscopy at the lowest practical frame rate, keep screening time honest, and document dose-area product as you would for any fluoroscopic intervention. Modern digital systems make excellent images at a fraction of the dose of a decade ago — but only if the operator lets them²⁵. Protecting staff is equally simple geometry: thyroid collars, lead aprons, and shielding drapes between the tube and the operator's hands.

4. Reading the images: interpretation atlas

A systematic read protects against the two classic errors of the HSG procedure: calling spasm disease, and calling disease normal because the wrong questions were asked. Read in the same order every time.

Cavity first

• Normal: smooth triangular cavity, sharp cornua, even opacification.
• Septate / subseptate: a persistent shelf or division from the fundus — distinguish from the duplicated external contour of bicornuate uterus with ultrasound correlation.
• T-shaped cavity: the classic DES-associated configuration — narrow, constricted, with reduced volume.
• Intrauterine adhesions (Asherman): irregular filling defects, ragged cavity outline, reduced volume; beading of contrast between synechiae.
• Filling defects: fixed, rounded defects — polyps or submucous fibroids; differentiate from mobile air bubbles by change between films.

Then the tubes

• Proximal (cornual) occlusion: no tubal filling; verify against spasm with slow injection and delayed film — a single-view diagnosis is a disservice¹².
• Distal (fimbrial) occlusion / hydrosalpinx: a sausage-shaped, non-spilling dilated tube; loculated spill suggests peritubal adhesions.
• Peritubal adhesions: saw-tooth tubal contour with loculated, delayed spill.
• Free spill: contrast curls freely around bowel — the normal endpoint.

A reporting skeleton worth standardizing

Consistent reporting is a gift to the referring clinician and to the patient who may carry this record between services. A compact structure works in nearly every service: technique and contrast used; adequacy of distension; cavity size, shape, and contour; cornual appearance and tubal filling to the fimbrial ends; character and timing of spill, including delayed films; impression in plain language with a clear next-step recommendation; and dose documentation. Services that adopt a template report measurably more consistently than those relying on memory — and consistency is what makes serial comparisons, and audit, possible¹².

When the study is indeterminate

A proportion of HSG procedures land in interpretive limbo: equivocal proximal occlusion that may be spasm, a single tube seen, poor distension in a patient who could not tolerate more. The professional response is to say so plainly and propose the right next test rather than the nearest one. Options include repeat HSG with slower technique and delayed films, selective salpingography to catheterize a single cornu directly, ultrasound-based tubal assessment with HyCoSy or HyFoSy foam, saline infusion sonography for the cavity, and — when anatomy and symptoms demand it — laparoscopy with chromopertubation as the definitive reference. Meta-analyses place the ultrasound techniques close to HSG in accuracy while sparing radiation, at the price of operator dependence^9,11,18.

5. The patient experience: pain and anxiety

Fear of pain is the single biggest barrier to women attending HSG, and anticipated anxiety measurably worsens perceived pain. The evidence base for mitigation is practical: pre-procedure analgesia, soft balloon catheters, gentle slow instillation, warm contrast, and even simple interventions like explaining the equipment before the examination all reduce pain scores^10,16,17,19. A systematic review of psychological interventions concluded that information and support are active treatments, not courtesies¹⁷.

Special situations

• Nulliparous or stenotic cervix: a slim balloon catheter and patient positioning often succeed where metal instruments fail; tenaculum use escalates pain sharply and should be a last resort¹⁶.
• Prior caesarean section: the cervical canal may be angulated; adjust traction and direction rather than force.
• Severe anxiety or vaginismus: schedule early, allow time, and consider sedation pathways per institutional policy — an abandoned HSG helps no one.
• Language and literacy barriers: translated information sheets and teach-back confirmation measurably improve experience and consent quality²⁰.

Explaining the procedure to patients

Every team member should be able to deliver this one-minute explanation: "We place a thin soft catheter through the cervix and, using X-ray guidance, gently fill the womb and tubes with a safe contrast dye that shows their shape on the screen. It takes about fifteen minutes. Most women feel period-like cramps during the test, which settle quickly — we inject slowly and warmly on purpose, because gentleness makes the pictures better and the test easier." An informed, calm patient lies still; a still patient gives the cleanest images. Patient-centred communication is diagnostic technique.

6. Beyond the test: therapeutic effect and the fertility pathway

An HSG procedure with oil-based contrast is one of the few imaging tests with a treatment effect. Pooled trial evidence shows improved ongoing pregnancy and live birth after oil-contrast flushing^2,6, and cost-effectiveness analyses favour it across healthcare systems^5,22. Clinically, the result slots into the pathway: normal tubes redirect workup toward ovulatory, male, and endometrial factors; bilateral occlusion redirects toward IVF; and a hydrosalpinx may prompt surgical correction before embryo transfer. Ultrasound alternatives — HyCoSy and saline infusion sonography — trade radiation for operator dependence, with comparable accuracy in experienced hands^9,11,18,21.

Choosing the right test for the right question

HSG, HyCoSy, and saline sonography are complements, not competitors. HSG with oil-based contrast leads when tubal patency and the therapeutic flushing effect are both in view; sonographic methods lead when radiation avoidance dominates — young patients needing repeated assessment, or services without dedicated fluoroscopy; hysteroscopy leads when intracavitary pathology is the primary suspicion^11,15,21. A service that can offer more than one test, and that chooses deliberately, serves patients better than a service that offers one test perfectly.

Whichever modality a service adopts, the discipline is identical: correct timing, correct contrast, gentle delivery, systematic reading, and a documented handoff to the referring clinician. The HSG procedure earns its place in the pathway when it is done well — and this module exists so that "done well" becomes your department's default.

Conclusion

The HSG procedure endures because it is fast, informative, and — done well — therapeutic. Its quality lives in the details: the day of the cycle, the temperature and character of the contrast, the patience of the injection, the discipline of the read, and the humanity of the explanation. None of these requires new technology; all of them can be taught, standardized, and certified.

That is the purpose of the SATMix HSG track: to make the gentle, evidence-based HSG procedure the default everywhere the test is performed. Master the seven essentials, and a five-minute fluoroscopic study becomes one of the most valuable interventions in reproductive medicine.

Start where you stand: audit your last twenty reports against the atlas in section four, time your injections, warm your contrast, and ask your patients what the experience was like. Small changes, honestly measured, compound quickly.