Pelvic Inflammatory Disease (PID): Ultrasound Findings

Name: Pelvic Inflammatory Disease (PID): Ultrasound Findings
Uploaded: 2025-07-20T20:48:02-06:00
Channel: Dr. Amar Udare, MD
Description: Explore comprehensive ultrasound techniques essential for diagnosing female pelvic emergencies, including ectopic pregnancy detection and critical imaging signs for timely intervention.

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Key facts for practice and radiology board exams

Pelvic inflammatory disease is a clinical diagnosis. Ultrasound is frequently normal in uncomplicated disease, so a normal transvaginal study does not exclude PID and antibiotics should not wait for imaging. Scan to find a pyosalpinx or tubo-ovarian abscess, which change management, and to exclude ectopic pregnancy and adnexal torsion.

Can ultrasound diagnose pelvic inflammatory disease?

Not on its own. The CDC treatment guidelines put PID on clinical criteria: presumptive treatment in a woman at risk with pelvic or lower abdominal pain and cervical motion, uterine or adnexal tenderness, with no other cause identified. Imaging sits among the more specific criteria, not the minimum ones, so it is not what starts treatment [1].

That is just as well, because early disease has little to show. Endometritis and mild salpingitis produce at most indistinct uterine and adnexal outlines, a trace of free fluid, or a thickened or fluid-filled endometrium. A review of the literature found transvaginal ultrasound has a limited ability to diagnose acute PID: the cogwheel sign is 95 to 99% specific but its reported sensitivity runs from 0 to 86%, and thickened tubal walls reach 100% sensitivity only once there is fluid in the lumen [2].

So the question a scan answers is not whether this is PID. It is whether there is an abscess, and whether this is something else.

Ultrasound findings in PID

The core finding is a dilated fallopian tube with a thickened wall. Seen in cross-section, the thickened longitudinal folds project into the lumen and give the cogwheel sign of acute salpingitis. Low-level internal echoes and a fluid-debris level make it a pyosalpinx. Once tube and ovary can no longer be told apart, it is a tubo-ovarian abscess.

Stage	Ultrasound finding	What it changes
Endometritis, early salpingitis	Often a normal study. Indistinct uterine and adnexal outlines, trace free fluid, thickened or fluid-filled endometrium	Nothing. Treat on clinical criteria
Acute salpingitis	Dilated tube, wall thicker than 5 mm, cogwheel sign in cross-section, incomplete septa	Confirms tubal involvement
Pyosalpinx	Dilated tube with low-level internal echoes and a fluid-debris level	Inpatient treatment, consider drainage
Chronic or treated disease	Thin-walled dilated tube, beads-on-a-string sign, no hyperaemia	Hydrosalpinx, not active infection
Periovarian inflammation	Enlarged ovary with multiple small peripheral follicles, adherent to the tube	Mimics polycystic ovary and torsion
Tubo-ovarian abscess	Complex adnexal mass, ovary not separable from it, thick hyperaemic wall, internal debris and septa	Drainage decision, longer antibiotics

Transvaginal ultrasound in pelvic inflammatory disease showing a dilated fallopian tube with a thickened wall, the appearance of pyosalpinx. — A dilated, thick-walled fallopian tube, the core ultrasound finding in acute PID. Imaged end-on, the thickened folds give the cogwheel sign.

Across 77 patients, the single best marker of tubal inflammatory disease was an incomplete septum within the dilated tube, present in 92% of cases, acute and chronic together. A thick wall and the cogwheel sign marked acute disease, while a thin wall and the beads-on-a-string appearance marked chronic disease [3]. That last distinction is the one worth protecting in the report: calling an old thin-walled hydrosalpinx acute PID overtreats the patient.

Tubo-ovarian abscess on ultrasound

The tubo-ovarian abscess is the finding that justifies the scan. It is a complex adnexal mass with a thick irregular wall, internal debris and septa, in which the ovary cannot be identified as a separate structure. Colour Doppler shows a hyperaemic wall with little or no internal flow.

Measure it, because size is the one number the gynaecologist will act on. There is no validated threshold, though. The cut-offs in the literature are retrospective and they disagree: one series of 102 patients found that a diameter over 7 cm, age over 40 and fever predicted failure of antibiotics and the need for secondary drainage [4], while other series put the cut-off nearer 5.5 cm. Report the maximum diameter and let it inform the decision rather than quoting a rule that does not exist.

What PID looks like on Doppler

Acute inflammation makes the adnexal mass hyperaemic. In 30 women studied against laparoscopy, power Doppler showed hyperaemia in every case of acute PID but in only 2 of 20 hydrosalpinx controls, with a pulsatility index of 0.84 against 1.50, giving 100% sensitivity and 80% specificity [5].

Treat that as the optimistic end of the evidence: the broader review concluded the opposite, that Doppler values overlap too much between women with and without PID to be diagnostically useful [2]. Its real value is comparative. A hyperaemic thick-walled tube is active disease, an avascular thin-walled one is an old hydrosalpinx, and a vascular wall around an avascular centre is an abscess rather than a solid tumour.

Pelvic emergencies mistaken for PID

All of these present as acute pelvic pain with an adnexal abnormality, and the first two are time-critical. Work through them before settling on PID.

Diagnosis	What separates it on ultrasound	Do not miss
Ectopic pregnancy	Positive hCG with no intrauterine sac, plus an adnexal mass separate from the ovary; tubal ring with a ring of fire on Doppler	The adnexal mass is 91% specific but only 64% sensitive [9]. Free fluid with low-level echoes means rupture
Interstitial ectopic	Eccentric sac with an interstitial line running from the endometrial cavity to the sac	The interstitial line is 80% sensitive and 98% specific; myometrial thinning alone is only 40% sensitive [10]
Adnexal torsion	Enlarged oedematous ovary with peripherally displaced follicles, follicular ring sign, midline displacement, whirlpool sign	Absent or reduced flow is 95% specific but only 53% sensitive, so normal Doppler does not exclude torsion [6]
Haemorrhagic cyst	Lace-like fibrin strands, fluid-debris level, no internal vascularity, crenulated margin once ruptured	Commonest benign cause of acute pelvic pain
Endometrioma	Homogeneous low-level internal echoes, avascular, longer history	Rarely torts, because adhesions tether the ovary
Appendicitis or diverticular abscess	Collection not separable from bowel, tubes and ovaries normal	Go to CT rather than hedging the origin of the collection
Malpositioned IUCD	Asymmetric limbs, device displaced toward the endocervix, loss of the T configuration	If the device is not seen and expulsion is denied, radiograph then CT
Ovarian vein thrombosis	Cord-like adnexal structure, usually postpartum; CT shows an enlarged vein with a filling defect	Easily missed prospectively on ultrasound
Ovarian hyperstimulation syndrome	Both ovaries massively enlarged with multiple cysts, ascites, recent IVF	Bilateral and symmetric, unlike infection
Mittelschmerz	Dominant follicle with a crenulated margin and trace free fluid, mid-cycle	A diagnosis of exclusion, not a reported abnormality

Transvaginal ultrasound showing an adnexal mass separate from the ovary in ectopic pregnancy, the main mimic of pelvic inflammatory disease. — Ectopic pregnancy: an adnexal mass lying separate from the ovary, with no intrauterine gestational sac.

Enlarged ovary with absent Doppler flow in adnexal torsion, a pelvic emergency that mimics pelvic inflammatory disease on ultrasound. — Adnexal torsion: an enlarged ovary with absent flow. Preserved flow would not have excluded the diagnosis.

Ultrasound showing an enlarged ovary alongside post-contrast MRI showing a non-enhancing twisted ovary in adnexal torsion. — The same torsed ovary on MRI, showing no enhancement.

Ultrasound of a malpositioned intrauterine contraceptive device with asymmetric limbs within the uterine cavity. — Malpositioned IUCD: asymmetric limbs and loss of the normal T configuration.

CT showing a dilated right ovarian vein with a filling defect, indicating ovarian vein thrombosis. — Ovarian vein thrombosis: an enlarged vein with a filling defect on CT. It is difficult to see on ultrasound.

CT showing massively enlarged ovaries and free fluid in ovarian hyperstimulation syndrome after IVF. — Ovarian hyperstimulation syndrome: bilateral massively enlarged ovaries with ascites after IVF.

When ultrasound is not enough

Use the transabdominal survey to check the kidneys and right lower quadrant as well, since ureteric calculi and appendicitis both present as pelvic pain. Transvaginal scanning resolves the tubes, but neither view is adequate in every case.

MRI outperforms ultrasound against laparoscopy, with a sensitivity of 95% and specificity of 89% against 81% and 78% for transvaginal ultrasound in the same 30 patients [7]. It is the problem solver when the clinical picture says PID and the ultrasound does not.
CT when a collection cannot be separated from bowel, when appendicitis or diverticulitis is in question, or to plan percutaneous drainage.
Do not assign an O-RADS score here. O-RADS US v2022 states the system does not apply to pelvic inflammatory disease or ectopic pregnancy. Note that a hydrosalpinx is a classic benign extraovarian lesion and scores O-RADS 2 at any size, so a score given in the wrong setting falsely reassures [8].

Transabdominal pelvic ultrasound using a full bladder as an acoustic window to show the uterus and adnexa. — Transabdominal scanning with a full bladder, the acoustic window for the initial survey.

Transvaginal ultrasound orientation showing the uterus and adnexa in the sagittal plane. — Transvaginal scanning gives the resolution needed to resolve the tubes.

How to report suspected PID

State whether a dilated tube is present, its wall thickness, and whether the contents are anechoic or echogenic. That one sentence separates hydrosalpinx from pyosalpinx.
Say whether the ovary is separable from the adnexal mass. If it is not, call it a tubo-ovarian abscess and give the maximum diameter in centimetres.
Record whether the collection is separable from bowel, and recommend CT if it is not.
Document that ectopic pregnancy and torsion were considered, with the hCG status and the ovarian arterial and venous Doppler findings.
If the study is normal, write that a normal pelvic ultrasound does not exclude PID. That is the single most useful line in the report.

Frequently asked questions

Can PID be seen on ultrasound?

Often not. Pelvic inflammatory disease is a clinical diagnosis and the scan is frequently normal in early or uncomplicated disease, because endometritis and mild salpingitis produce only non-specific changes. Ultrasound becomes useful once the fallopian tube dilates. A normal study does not exclude PID and should not delay antibiotics.

What does PID look like on ultrasound?

The core finding is a dilated fallopian tube with a wall thicker than 5 mm. In cross-section the thickened folds give the cogwheel sign. Low-level internal echoes and a fluid-debris level indicate pyosalpinx. In advanced disease tube and ovary merge into a complex adnexal mass with a thick hyperaemic wall, which is a tubo-ovarian abscess.

What is the cogwheel sign in PID?

A thick-walled fallopian tube imaged in cross-section, in which the thickened longitudinal mucosal folds project into the lumen like the teeth of a cogwheel. It indicates acute salpingitis and is 95 to 99% specific, although reported sensitivity ranges from 0 to 86%. The beads-on-a-string sign, small mural nodules in a thin-walled dilated tube, indicates chronic disease instead.

How do you tell a tubo-ovarian abscess from an ovarian cyst?

A tubo-ovarian abscess has a thick irregular wall, internal debris and septa, and a hyperaemic wall on colour Doppler, and the ovary cannot be identified separately from it. A simple or haemorrhagic cyst has a thin wall, no wall hyperaemia, and recognisable ovarian tissue around it.

Does a normal pelvic ultrasound rule out pelvic inflammatory disease?

No. Transvaginal ultrasound has a limited ability to diagnose acute PID, and the early disease has no reliable sonographic signs, so treatment is started on clinical criteria alone. If suspicion persists and the ultrasound is normal, MRI is the more sensitive next test, at 95% against 81% for ultrasound in a comparison against laparoscopy.