PID & Tubo-Ovarian Abscess
- Pelvic inflammatory disease (PID) is an infection that climbs up from the cervix into the uterus, tubes, and ovaries — bacteria taking the stairs the wrong way.
- A tubo-ovarian abscess (TOA) is the endgame: a walled-off bag of pus where the tube and ovary have melted together into one angry, thick-walled mass.
- Ultrasound is the first look; CT or MRI helps when the picture is fuzzy or you're worried about how far the infection has spread.
- The single image you're hunting for is a complex, thick-walled, fluid-filled adnexal mass in a sick, tender patient — pus until proven otherwise.
- This is a "don't sit on it" diagnosis: a TOA can rupture, and a ruptured one is a surgical emergency.
Most infections in the pelvis have the decency to stay put. PID does not. It starts as a garden-variety cervical infection and then, instead of clearing out, marches upward — cervix, uterus, fallopian tubes, ovaries — like a houseguest who keeps wandering into rooms they weren't invited to. By the time imaging gets involved, that houseguest has often trashed the place.
What PID actually is
PID is an ascending infection of the upper female genital tract. The usual culprits are sexually transmitted organisms (think Chlamydia and gonorrhea), often with other bacteria joining the party once the tissue is inflamed and welcoming.
Here's the key mental model: the infection travels along surfaces. It coats the lining of the uterus (endometritis), then the tubes (salpingitis), then spills onto the ovaries and out into the pelvis. Each step up that ladder gives you a different imaging finding, and the further up the ladder, the sicker the patient.
PID is mostly a clinical diagnosis — lower abdominal pain plus cervical motion tenderness on exam buys treatment, no imaging required. We image when the diagnosis is uncertain, when the patient isn't improving, or when we're worried she's tipped over into an abscess.
The imaging ladder, rung by rung
Early PID is sneaky. On ultrasound, mild disease can look almost normal, which is its favorite trick. As things worsen, findings show up in roughly this order:
| Stage | What's inflamed | What you see |
|---|---|---|
| Endometritis | Uterine lining | Thickened endometrium, a little fluid or gas in the cavity, indistinct uterine borders. |
| Salpingitis | Fallopian tube | Thickened, fluid-filled tube; pus inside a tube (pyosalpinx) shows debris and incomplete septa. |
| TOA | Tube + ovary fused | Complex, thick-walled multilocular mass; ovary no longer separable from the tube. |
A quick word on that tube. A healthy fallopian tube is so thin you basically never see it. So when a dilated, fluid-filled tube appears, that alone is a red flag. The classic look is a folded, tubular structure with incomplete septa — little internal flaps that don't quite reach across, because they're just the wall of the tube doubling back on itself as it kinks. Picture a kinked garden hose that's been filled with murky water: the bends look like walls, but they don't fully wall anything off.
The main event: tubo-ovarian abscess
A tubo-ovarian abscess is what happens when salpingitis keeps going and the infection eats through tissue planes until you can no longer tell where the tube ends and the ovary begins. They become one mass — a thick-walled bag of pus.
On ultrasound, a TOA is a complex adnexal mass: a thick, often shaggy wall; internal fluid with low-level echoes (that's debris and pus, not clear fluid); and sometimes septations or a gas-fluid level. Color Doppler typically shows a fired-up, hyperemic wall — the body throwing blood flow at the infection.
On CT, you'll see a thick-walled, rim-enhancing fluid collection in the adnexa, usually with inflammatory stranding smudging the fat around it and thickening of the nearby structures. CT shines for mapping how far things have spread — into the cul-de-sac, up the gutters, anywhere pus likes to pool.
A TOA in a postmenopausal woman is a different animal — it's far less likely to be plain old PID and should make you think about an underlying malignancy or a perforated GI process (like a complicated appendicitis or diverticulitis) seeding the adnexa. The age changes the whole conversation.
Don't get fooled
The trap with a complex adnexal mass is that pus, blood, and tumor can all look like "messy fluid behind a thick wall."
A TOA can mimic — and be mimicked by — an endometrioma, a hemorrhagic cyst, a ruptured ectopic pregnancy, or an ovarian neoplasm. The deciding vote is the patient: fever, elevated white count, cervical motion tenderness, and the right risk profile push you toward infection. Imaging rarely makes this call alone.
And don't forget to look above the pelvis. PID can track up to the liver and inflame its capsule — perihepatic inflammation classically described as "violin-string" adhesions (the Fitz-Hugh–Curtis pattern). On CT you may catch a thin rim of enhancement along the front of the liver. It's a small finding that tells a big story: this infection did not stay in its lane.
Why the urgency
An intact TOA can often be treated with antibiotics, with drainage if it's large or stubborn. A ruptured TOA spills pus into the peritoneum and can cause sepsis — that's a surgical emergency.
So the job of imaging isn't just "is there an abscess?" It's also "is the wall intact, how big is it, and is there free fluid suggesting it has blown?" Catching a TOA while it's still a contained, angry bag — rather than after it bursts — is the entire point. Find the thick-walled, debris-filled adnexal mass in a sick, tender patient, call it what it is, and don't wait around to see what it does next.