Pelvic inflammatory disease (PID) is one of common infectious diseases among women.
The etiology of PID is an ascending infection of female genital tract caused by microorganisms sexually transmitted.
By spreading bacteria from the vagina to the cervix,
adnexa and the peritoneal cavity,
PID is considered series of infection as cervicitis,
endometritis,
pyometra,
salpingitis,
oophoritis,
pyosalpinx,
tubo-ovarian abscess (TOA).
Many risk factors include multiple sexual partners,
younger age,
previous uterine procedure and intrauterine devices,
IUD.
Common and clinical symptoms of PID are known as pelvic pain,
fever and vaginal discharge,
however,
PID sometimes presents asymptomatic and is possible to spread to pelvic peritonitis resulting to infertility and ectopic pregnancy among young women.
Depended on clinical manner,
PID is classified into early or late stage.
As late complications,
various types of peritonitis were caused by uterine and/or tubo-ovarian abscess rupture,
ileus caused by peritoneal adhesions,
peri-hepatitis spreading to the upper portion that is known a Fits-Hugh-Curtis syndrome (1-5).
TOA is classically treated with antibiotics,
however,
this initial process sometimes requires surgical procedure additionally at the risk of 25% with drainage for abscess,
salpingo-ophorectomy and hysterectomy (1,6) (Fig.1).
For the appropriate management of PID,
radiologists are required to make differentiate PID from mimics of PID including pelvic endometriosis,
torsion of adnexa,
hemorrhagic ovarian cyst,
neoplasms of adnexa,
appendicitis,
diverticulitis and urinary tract infection (7).
To make diagnosis PID,
transvaginal ultrasound (TVUS),
CT and/or MRI are chosen generally in many institutions.
At first,
TVUS are usually available to make diagnosis following physical examination (8-10).
The sensitivity of TVUS for detecting pyosalpinx was reported 97% (11).
With presenting nonspecific symptoms,
CT contributes to differ gynecologic from non-gynecologic disease and to help to confirm the extent of infection beyond the pelvis (8).
This application enables to lead the adequate management (10).
The specificity of CT for predicting salpingitis was reported more than 90%.
(11).
On the other hand,
MRI is superior to provide precise information based on soft tissue contrast than CT and TVUS and to evaluate signal intensity of hemorrhage,
pus and internal changes of infected focus (9,12).
MRI also contributes to make differentiate abscess from cystic lesion combined restricted diffusion with contrast enhancement in advanced PID.
The sensitivity,
specificity and accuracy of conventional MRI were 90.7%,
93.3% and 91.2%.
Meanwhile,
the sensitivity,
specificity,
accuracy of MRI combined with DWI were 98.4%,
93.3% and 97.5% for detecting PID (13) (Fig.2).
TOA commonly demonstrats cystic mass with thick irregular walls,
septa and internal echoes,
and no peristalsis on TVUS findings.
Typical CT and MR imaging of TOA presents cystic masses with thick wall,
internal septa and surrounding inflammatory changes.
The content of TOA usually shows heterogeneously high signal intensity on T2WI and low signal intensity on T1WI that depends on protein concentration.
The content of abscess is reported hyperintense on DWI and hypointense on ADC map due to restricted diffusion (12,16).
Pyosalpinx describes fluid-full tubular structure dilatated with wall thickening.
TVUS findings demonstrate an adnexal mass with solid,
cystic or complex (12).
CT imaging shows inflammatory changes with increased attenuation of adjacent fat tissue.
MR imaging presents cystic with high signal intensity on T2WI and lack of internal enhancement (14).
Pyometra demonstrates the uterine cavity distended with pus and fat attenuation increased around uterus on CT image.
Gas bubbles and air-fluid level are sometimes seen within the uterine cavity (2) (Fig.3).
Unusual causes of PID include actinomycosis,
tuberculosis and xanthogranulomatous infection.
Actinomycosis:
On CT imaging,
TOA caused by actinomycosis predominantly demonstrates solid or a solid and cystic mass in the adnexa.
The solid component shows contrast enhancement prominently.
IUDs are found in many cases.
Small abscess is also be recognized with peripheral enhancement.
Inflammatory changes are characteristic with extension from the solid mass to the adjacent tissue.
On MR imaging,
solid mass shows heterogeneous and low signal intensity on T2WI to represent fibrotic features.
Inflammatory extension appears thick and linear with low signal intensity on T2WI and with well enhancement.
Direct invasion into the adjacent tissue makes difficult to differentiate ovarian malignancies.
Tuberculosis:
Genital tuberculosis is rare but commonly involves fallopian tubes that causes granulomatous salpingitis.
In result,
tubal occlusion occurs at the isthmus and ampulla due to severe scar.
Tuberculous TOA is caused when tuberculosis involves the ovaries.
Tuberculous peritonitis occurs less common than salpingitis,
however,
it causes a large amount of ascites and peritoneal thickening that resembles peritoneal dissemination.
On MR imaging,
wall thickening of tuberculous TOA is irregular and shows low signal intensity on T2WI compared with smooth wall thickening of usual TOA.
xanthogranulomatous inflammation:
Xanthogranulomatous inflammation is rare and chronic inflammation,
and commonly affects the kidney and gallbladder.
Xanthogranulomatous oophoritis is reported rarely but is mentioned to demonstrate multiple nodules in the wall of a cystic mass shows low signal intensity on T1WI,
high signal intensity on T2WI and deficit of contrast enhancement (15,16) (Fig.4).
As an entity of mimicking PID,
we encounter commonly with infected endometriotic cyst,
degenerating uterine leiomyoma and ovarian tumours.
infected endometriotic cyst
The incidence of TOA was reported 2.3% with patients with endometriotic cyst and 0.2% in patients without endometriotic cyst.
The reason why endometriotic cyst increases incidence with TOA,
immunological factor,
wall weakness of endometriotic cyst against bacterial invasion and the blood content of cyst as a culture of infection (17,18).
On both of CT and MRI,
infected endometrioma shows peripheral fat attenuation increased,
however,
MRI is superior to differentiate TOA from infected endometriotic cyst
degenerating uterine myoma
Several types of degenerating leiomyoma are known as hyaline,
cystic,
myxoid and red degeneration.
It causes acute abdominal pain and fever with patients that overlap PID.
On US findings,
degenerating leiomyoma show heterogeneous.
MRI is helpful to demonstrate inhomogeneous signal intensity and lack of contrast enhancement (3,12).
ovarian tumours
Although the clinical course of acute PID and ovarian malignancy is usually different,
some chronic abscess becomes to be difficult make differentiating from ovarian malignancies on MR imaging (13).
MR findings of ovarian tumor with wall thickening and internal architecture might be helpful to remind malignancy with acute onset of abdominal pain (Fig.5).