The best imaging modality for diverticulitis assessment is undoubtedly CT,
especially for its ability to diagnose diverticulitis complications (e.g.: abscesses,
perforation).
Nevertheless,
in our daily practice,
when there is not a clear suspicion of diverticulitis,
the diagnostic algorithm of lower left abdominal pain generally starts with US abdominal and pelvic examination.
US has similar sensitivity and specificity to CT in cases of uncomplicated diverticulitis.
It has some advantages relatively to CT including the lower cost,
the wider availability and the absence of ionizing radiation.
On the other side,
US is operator-dependent and its accuracy is diminished when diverticulitis complications arise.
When the following imaging findings are observed,
the diagnosis of diverticulitis can be assured and CT is not necessary,
unless disease complications are suspected ( Fig. 4 ):
-
- Thickening of the bowel wall.
Mild and uniform wall thickening (wall thickness generally not greater than 5mm on the short axial,
with correctly distended colonic lumen),
that usually extends for a segment larger than 5cm;
- Inflamed diverticulum.
Round echogenic structure with posterior ring-down artifact or a surrounding hypoechoic rim;
- Inflamed pericolic fat.
Increased echogenicity of the pericolic fat.
On the other side,
if diverticulitis is clearly the suspected diagnosis,
there is no need to use US in first place,
and CT is the study to order.
These are the imaging findings that suggest the presence of diverticulitis ( Fig. 5, Fig. 6 ):
- Inflamed diverticulum.
Focal,
paracolic outpouching (diverticulum),
with ill-defined limits,
centered within inflamed fat ;
- Inflamed pericolic fat.
Haziness and stranding of the pericolic fat that is usually very pronounced and disproportionate to the degree of wall thickening;
- Thickening of bowel wall.
As previously described.
The transition between the normal and thickened wall is progressive,
without “shouldering”;
- Microperforation.
Small pockets of extraluminal gas ( Fig. 7 , Fig. 8 );
- Centipede sign.
Representing engorgement of the vasa recta that “feed” the colonic segment where the diverticulum is located ( Fig. 9 );
- Comma sign and reverse comma sign.
These signs represent thickening of the lateroconal fascia,
a finding frequently seen in colonic diverticulitis (it is nevertheless an unspecific finding,
associated to other pathologies).
“Comma sign” is a left-sided finding,
secondary to descending/sigmoid diverticulitis,
while “reverse comma sign” occurs in the right side,
secondary to right-side diverticulitis ( Fig. 10 ).
- COMPLICATIONS OF DIVERTICULITIS
Generally diverticulitis is a self-limited process yet frequently recurrent,
resolving without sequelae when the treatment is adequate.
In most cases treatment is simple,
involving bowel rest,
intravenous hydration and antibiotherapy.
However,
complications can occur,
difficulting the resolution of the inflammatory process and adding long-term morbidity to diverticular disease.
As previously described,
CT is the advised imaging resource to evaluate these possible events.
The most important complications of diverticulitis are:
ABSCESS ( Fig. 11 )
Pericolic abscess is a frequent complication of diverticulitis,
occurring in up to 30% of cases.
Small abscesses (< to 4cm) are generally managed medically,
with antibiotherapy.
When larger than 4cm,
diverticular abscesses should be treated by drainage.
Because of portal venous inflow,
hepatic abscesses can infrequently occur and imaging guided drainage can also be necessary.
Imaging findings: fluid collection with contrast-enhancing walls.
It may present gas in its interior.
PERFORATION ( Fig. 12 )
Gross perforation is a rare complication occurring in 1-2% of the cases.
If not treated quickly and appropriately,
the spillage of colonic content soon induces fecal peritonitis,
aggravating the prognosis.
The risk of colonic perforation is the reason why diagnostic procedures like barium enema or colonoscopy are contraindicated in the evaluation of acute diverticulitis.
Imaging findings: free intra-abdominal air associated with ascites and enhancement and thickening of the peritoneum if peritonitis develops.
FISTULAE ( Fig. 13 )
Fistulization arises when inflammatory changes resulting from perforation erode the skin or adjacent viscera.
It involves most frequently other colonic segments and the bladder (up to 65% of cases).
(Diverticulitis,
nejm) Fistulous tracts to the skin or female pelvic organs can also occur,
but are less frequent.
Imaging findings: colo-colonic fistulae are difficult to detect but occasionally a sinus tract with gas in its interior can be seen communicating two segments of colon,
with inflammatory changes of nearby tissues.
In the case of bladder fistulization,
the most frequent and significant finding is the presence of endoluminal gas bubbles.
OBSTRUCTION ( Fig. 14 )
Small bowel or colonic obstruction can be an acute,
subacute or chronic complication of diverticulitis,
impeding the passage of enteric / fecal bowel content,
with surgical correction being frequently necessary.
When the obstruction is secondary to chronic diverticulitis the findings can be quite similar to colorectal cancer.
Imaging findings: caliper reduction of bowel segment with dilation of upstream intestinal segments.
In cases of chronic diverticulitis,
the presence of diverticula is the single strongest morphological feature pointing to this diagnosis.
Other suggestive finding is the presence of a long segment (generally > 10 cm) of mildly thickened colon.
PYOPHLEBITIS ( Fig. 15 )
Pyophlebitis represents thrombosis of mesenteric or portal veins secondary to intra-abdominal inflammatory or infectious process,
including diverticulitis.
It has a poor prognosis.
Imaging findings: absence of opacification of portal or systemic venous vessels that is generally associated to some degree of vessel engorgement.
The clinical picture of diverticulitis is quite unspecific and can be seen in different pathologies,
from vascular to neoformative,
inflammatory and other kind of insults.
Despite this,
there are some differences that can help attaining a specific diagnosis.
COLORECTAL CANCER ( Fig. 16 )
One of the most important differential diagnosis of diverticulitis is colon adenocarcinoma,
and the imaging overlap between these 2 pathologies is estimated to be around 10%.
Adenocarcinoma of the colon is most frequently seen in the descending or sigmoid segments and,
like diverticulitis,
can also be associated with complications like obstruction,
perforation or fistulization.
Key imaging findings: colorectal neoplasms are generally seen as a short (˂ 5cm) segment of severe,
irregular,
non-stratified and eccentric thickening of the colonic wall,
with sudden transition between the normal and abnormal wall.
The inflammatory changes of pericolic tissues are minimal (except when complications are seen) and local lymphadenopathies are usually present.
DIAGNOSTIC PEARL: the disproportion between the large degree of colonic wall thickening and the slight pericolic fat densification and stranding.
Presence of lymphadenopathies.
Sigmoidoscopy after the resolution of acute symptoms may be useful is doubtful cases.
EPIPLOIC APPENDAGITIS ( Fig. 17 )
This is a relatively rare ischemic and inflammatory condition that occurs with torsion and subsequent ischemia of the epiploic appendages,
pedunculated fatty structures arranged over the external aspect of the colon that extend from the cecum to the rectosigmoid junction.
Imaging findings: at CT there is a small (1-4cm) ovoid paracolic lesion with fat density,
surrounded by hyperdense rim (representing the inflamed visceral peritoneum that covers the appendage),
with a small central dot that represents engorged or thrombosed vessels.
There is densification and stranding of the pericolic fat with mild and asymmetric thickening of the adjacent colonic wall.
DIAGNOSTIC PEARL: thetypical aspect of an ovoid paracolic fatty lesion with inflammatory changes in the pericolic fat and slight thickening of the bowel wall.
OMENTAL INFARCTION ( Fig. 18 )
Like epiploic appendagitis,
infarction of the omentum also occurs with torsion and vascular insults resulting from trauma or spontaneous thrombosis of the omental veins.
It is more frequent at the right quadrants of the abdomen,
but can occur wherever there’s omentum.
Imaging findings: large non-enhancing mass (generally > 5cm) with heterogeneous attenuation,
representing the infarcted tissue and pericolic inflammation.
Slight bowel thickening can occur but is extremely disproportionate relatively to the large ischemic and inflammatory mass.
DIAGNOSTIC PEARL: the disproportion between the large inflammatory mass (greater than epiploic appendagitis) and the slight degree of thickening involving a short segment of colon.
INFLAMMATORY BOWEL DISEASE ( Fig. 19 )
Inflammatory bowel disease is divided in 2 similar idiopathic entities most frequently diagnosed in early adulthood: Crohn disease and ulcerative colitis.
While Crohn disease most frequently involves the small bowel and the right colon with “skip areas” between the pathologic bowel segments,
ulcerative colitis is limited to the colon and rectum (the terminal ileum may also be involved due to “backwash ileitis”) in a continuous pattern – without “skip areas”,
being typically left-sided.
It is important to notest that the rectum is always involved in ulcerative colitis,
constantly presenting inflammatory changes unless the patient is being treated with anti-inflammatory enemas.
The rectum is typically spared in Crohn disease.
In this group of diseases it is acute ulcerative colitis that can be confounded with diverticulitis because,
like diverticulitis,
it generally occurs in the left-sided colon.
Imaging findings: in acute ulcerative colitis the segment of inflamed bowel is generally more extensive than in diverticulitis (sometimes a pancolitis occurs) and the thickening is symmetric and occasionally stratified - “water halo sign” (representing submucosal edema,
an unspecific finding seen in different types of colitis).
DIAGNOSTIC PEARL: the large extension of colonic inflammatory involvement.
There may be sequelae of chronic inflammation as the “fat halo sign” (representing submucosal fat deposition),
proliferation of peri-rectal fat or the “lead pipe sign” (representing loss of normal haustral markings,
luminal narrowing and bowel shortening).
INFECTIOUS COLITIS ( Fig. 20 )
There is a large number of microorganisms that can cause colitis and frequently the clinical and imaging findings overlap.
Most of them can manifest as pancolitis,
while some agents have predilection for the right colon (e.g.: tuberculosis) and others for the left colon (e.g.: shigellosis).
There is a subtype of infection that should be highlighted due to its etiology and severity – pseudomembranous colitis.
Pseudomembranous colitis is caused by Clostridium difficile,
a commensal gastrointestinal organism that overgrows with antibiotherapy or chemotherapy,
causing bowel damage due to the production of exotoxins.
The majority of patients is affected by diffuse diarrhea and abdominal cramps,
consequence of superficial mucosal disease.
However,
severe cases can progress to toxic megacolon with pronounced colonic distension and risk of transmural injury and perforation.
Imaging findings: the different types of infectious colitis are associated to colonic wall thickening,
pericolic densification and stranding,
with possibility of ascites.
Severe cases of pseudomembranous colitis however,
present with markedly thickened and edematous bowel wall with irregular and polypoid mucosal contour.
The degree of wall thickening may reveal the accordion sign,
representing entrapment of positive oral contrast between the thickened bowel haustra.
The colonic diameter may be greatly augmented.
DIAGNOSTIC PEARL: the infectious clinical and laboratorial picture,
and the large extension of colonic inflammatory changes.
ISCHEMIC COLITIS ( Fig. 21 )
Acute ischemic colitis is the most common form of intestinal ischemia,
being almost invariably associated to sudden hypoperfusion,
affecting predominantly the elder generation.
The colonic segments more frequently involved are the “watershed areas” like the splenic flexure (Griffith point,
representing the junction between the distribution of the superior and inferior mesenteric arteries) and the rectosigmoid junction (point of Sudeck,
representing the anastomotic plexus between the inferior mesenteric artery distribution and the hypogastric vascular supply) (CT Imaging of Colitis).
Clinically it ranges from transient episodes of mucosal and submucosal ischemia to catastrophic cases of transmural infarction with bowel necrosis.
Imaging findings: generally there are unspecific findings of segmental involvement of the colon traduced by various degrees of wall thickening.
The length of the involved colon is varied,
ranging from small segments (around 5cm) to involvement of the whole colon (which is infrequent).
The thickened wall is generally edematous,
enhancing homogeneously or heterogeneously.
Varying degrees of pericolic densification may follow and ascites can be seen.
In severe cases circumferential intra-mural air can be seen – pneumatosis coli,
occasionally followed by portomesenteric venous gas,
suggesting transmural necrosis.
DIAGNOSTIC PEARL: theendoscopic visualization of petechiae and eritematous mucosa in the acute phase,
evolving to cyanotic and ulcerated mucosa in severe cases.
It is important to emphasize that the clinical / radiological suspicion of ischemic colitis is confirmed by colonoscopy.
FOREIGN BODY PERFORATION ( Fig. 22 )
Ingestion of a non-digestible item is a relatively common finding,
especially in people who wear dentures as the recognition of small intra-oral objects is reduced due to the incapacity of taking advantage of soft palate tactile sensitivity.
Digestive tract perforation is a rare finding however,
generally associated to sharp objects (animal bones,
toothpicks,
metal objects) and it occurs occasionally in the colon but most frequently in the small bowel.
Clinical findings may vary from slight abdominal pain and nausea to established peritonitis.
Imaging findings: if dense enough,
perforating foreign bodies can usually be seen as linear structures traversing the bowel wall.
It is more probable to identify metallic and bony objects than pieces of wood (like toothpicks).
Additional findings like small bubbles of extraluminal gas adjacent to an area of thickened bowel wall and densified/stratified mesenteric fat,
frequently associated to an extramural abscess,
support this diagnosis.
DIAGNOSTIC PEARL: thevisualization of a linear hyperdense structure traversing the bowel wall associated to colonic and pericolic inflammatory findings.
INFLAMMATORY PELVIC DISEASE (IPD) ( Fig. 23 )
Inflammatory and infectious disease of the upper genital tract is a relatively frequent diagnosis,
generally seen in sexually active young females.
The use of contraceptive intrauterine device is a risk factor.
Clinically,
IPD manifests with lower abdominal pain,
abnormal vaginal discharge,
utero-anexial tenderness and fever with leucocytosis.
The diagnosis is supported by imaging,
mainly ultrasound.
Complications like endometrits,
salpingitis,
tubo-ovarian abscess or even peritonitis can develop in some cases.
Occasionally,
inflammatory changes resulting from advanced or complicated IPD can involve adjacent pelvic segments of bowel and mesenteric fat,
making difficult to distinguish this diagnosis from other pathologies as diverticulitis.
Imaging findings: the first line examination for suspected IPD is endocavitary ultrasound.
Possible sonographic findings include endometrial thickening with or without fluid/gas,
ovarian and uterine enlargement with poorly defined borders,
free intraperitoneal fluid and pelvic mesenteric fat inflammation.
Complicated tubo-ovarian abscesses can originate complex adnexal masses.
CT in IPD is mainly used to evaluate possible complications (e.g.: tubo-ovarian abscesses) or when it is necessary to exclude other possible differential diagnoses.
At CT,
non-complicated DIP does not present significant findings,
except perhaps a small amount of fluid in the cul-de-sac.
With advanced cases and progression to tubo-ovarian abscess,
findings include thick-walled,
septated,
low attenuation complex masses,
occasionally associated to serpiginous structures,
representing the dilated fallopian tubes.
Internal gas is a quite specific but very unusual finding.
Thickening of the uterosacral ligaments,
increased attenuation of the presacral fat and loss of definition of the margins of adjacent bowel loops suggest the diagnosis of IPD.
DIAGNOSTIC PEARL: the clinical picture of a febrile young woman with abnormal vaginal discharge with good response to antibiotics,
associated to utero-anexial positive imaging findings is suggestive of IPD.