Cystitis is inflammation of the bladder wall, most commonly due to bacterial infection (acute bacterial cystitis), but viral, fungal, radiation, chemical (cyclophosphamide), interstitial, and eosinophilic forms also exist. Acute bacterial cystitis is the most common urinary tract infection in the community, predominantly in women (lifetime prevalence 50-60% in women). On imaging, it is characterized by diffuse or focal bladder wall thickening, mucosal enhancement, perivesical fat stranding, and intraluminal debris/gas. Emphysematous cystitis is a severe form defined by the presence of gas within the bladder wall, caused by gas-forming organisms (E. coli, Klebsiella, Clostridium) in diabetic and immunosuppressed patients — intramural and/or intraluminal gas on CT is pathognomonic. Hemorrhagic cystitis is characterized by widespread hemorrhage in the bladder wall and is most commonly due to cyclophosphamide, radiotherapy, or viral infections (BK virus, adenovirus). Interstitial cystitis (bladder pain syndrome) is a non-infectious inflammatory condition characterized by chronic pelvic pain and urinary frequency; imaging shows a small-capacity, thick-walled bladder. Eosinophilic cystitis is rare, characterized by eosinophilic infiltration of the bladder wall; imaging may show focal or diffuse wall thickening mimicking tumor.
Age Range
15-85
Peak Age
45
Gender
Female predominant
Prevalence
Common
In acute bacterial cystitis, pathogens (most commonly E. coli 80-90%) reach the bladder from periurethral colonization via ascending route → adhere to urothelial mucosa via adhesins (P-fimbriae, type 1 fimbriae) → inflammatory cascade activates → neutrophil and macrophage infiltration → mucosal edema, vascular congestion, and increased capillary permeability. Imaging correlation: mucosal edema and congestion → diffuse wall thickening on CT (normal <3 mm → 5-15 mm in inflammation); increased vascular permeability → mucosal enhancement on contrast-enhanced CT (inner layer enhancement); inflammatory exudate and edema extend to perivesical fat → perivesical fat stranding. In emphysematous cystitis, gas-forming organisms (E. coli, Klebsiella, Clostridium) produce CO2 and H2 gas through glucose fermentation in the bladder wall — high tissue glucose in diabetic patients accelerates this process. Produced gas accumulates between bladder wall layers (intramural gas) and/or leaks into the bladder lumen (intraluminal gas). Gas has negative HU value (-1000 HU) on CT and creates very conspicuous contrast in soft tissue. In hemorrhagic cystitis, cytotoxic agents (cyclophosphamide metabolite acrolein) or radiation damage the urothelium → mucosal ulceration → subepithelial vascular injury → hemorrhage. On US, intraluminal clots appear as hypoechoic/mixed echogenicity structures with gravity-dependent layering. In chronic/interstitial cystitis, prolonged inflammation → detrusor fibrosis → decreased bladder capacity → thick-walled, low-capacity bladder (small-volume bladder + diffuse wall thickening on CT/MRI).
Gas-density (-1000 HU) bubbles or linear collections within the bladder wall are pathognomonic for emphysematous cystitis. CO2 and H2 gas produced by gas-forming organisms through glucose fermentation in the bladder wall accumulates intramurally. Seen in diabetic and immunosuppressed patients and requires emergent treatment.
Diffuse symmetric wall thickening (>5 mm, normal <3 mm) is seen on contrast-enhanced CT. The mucosal layer (inner layer) shows prominent enhancement — described as 'target sign' or 'halo sign': enhancing mucosa (hyperattenuating inner ring) + edematous submucosa (hypoattenuating middle ring) + muscle layer (isoattenuating outer ring). Thickening is usually diffuse and symmetric; focal thickening should raise concern for malignancy. Perivesical fat stranding may accompany. In acute bacterial cystitis wall thickening is homogeneous, while in emphysematous cystitis it appears fragmented with intramural gas foci.
Report Sentence
Diffuse symmetric bladder wall thickening (__ mm) with mucosal enhancement (target/halo sign) is seen; consistent with acute cystitis.
In emphysematous cystitis, small bubbles or linear gas collections of gas density (-1000 HU) are seen within the bladder wall. Gas may involve all layers of the bladder wall and intraluminal gas-fluid level may accompany. Gas distribution: (1) intramural — air bubbles/linear streaks within the wall; (2) intraluminal — air-fluid level in the bladder lumen; (3) perivesical — gas extension beyond the bladder in advanced cases (poor prognosis). CT is the most sensitive modality for these findings — plain radiograph and US are less sensitive for gas detection. Emphysematous cystitis represents an emergency requiring IV antibiotics + bladder decompression.
Report Sentence
Intramural gas foci are seen within the bladder wall, consistent with emphysematous cystitis; IV antibiotics and bladder decompression are recommended given clinical urgency.
Haziness (fat stranding) and linear density increases in perivesical fat tissue around the bladder are seen on contrast-enhanced CT. This finding indicates the inflammatory process has extended beyond the bladder wall to surrounding tissues. Mild stranding is seen in uncomplicated cystitis, while marked stranding and fluid collection indicate complicated cystitis (abscess, perforation). Perivesical stranding is not specific to cystitis — bladder tumor, radiation, and post-surgical changes can also produce similar appearance.
Report Sentence
Perivesical fat stranding is seen, indicating extension of the inflammatory process beyond the bladder.
Diffuse symmetric wall thickening is seen on B-mode ultrasound (normal <3 mm in distended bladder, >5 mm in cystitis). Wall echogenicity may be increased or hypoechoic internal band may be visible due to submucosal edema (US target sign). Intraluminal low-level echoes (debris) in acute bacterial cystitis represent purulent material. In hemorrhagic cystitis, intraluminal clots appear as hypoechoic/heterogeneous structures. In emphysematous cystitis, bright echogenic foci + 'dirty shadow' within the wall indicate gas presence.
Report Sentence
Diffuse symmetric wall thickening (__ mm) with intraluminal debris is seen in the distended bladder; consistent with acute cystitis.
High signal is seen in the bladder wall on T2-weighted MRI due to inflammation — submucosal edema appears as a markedly hyperintense band on T2. Wall thickening is diffuse and symmetric as on CT. T2 hyperintense wall + enhancement on T1 (post-gadolinium) indicates active inflammatory process. On DWI, inflammatory tissue may show mild diffusion restriction. In hemorrhagic cystitis, T1 hyperintense areas (methemoglobin) are seen within the wall or in intraluminal clots. The main advantage of MRI in cystitis evaluation is superior soft tissue contrast — particularly useful for wall layer discrimination and muscle invasion assessment.
Report Sentence
Diffuse high signal in the bladder wall on T2-weighted sequence (submucosal edema) with mucosal enhancement on contrast-enhanced T1 is seen; consistent with active inflammatory process (cystitis).
Mild-to-moderate diffusion restriction may be seen in the inflamed bladder wall on DWI — increased signal along the wall at high b-value and mildly low signal on ADC map. However, this finding cannot be reliably distinguished from tumor diffusion restriction. Intraluminal purulent collections show marked diffusion restriction — water molecule movement is restricted in viscous protein-rich purulent fluid. Artifacts (susceptibility, distortion) should be noted in DWI bladder evaluation.
Report Sentence
Mild diffusion restriction is seen in the bladder wall on DWI; compatible with inflammatory cell infiltration, clinical correlation is recommended for malignancy differentiation.
Criteria
Most common form (>90%); E. coli dominant (80-90%); very common in women; dysuria, frequency, suprapubic pain; positive urine culture; diffuse wall thickening + mucosal enhancement on CT; usually does not require imaging.
Distinct Features
Wall thickening is homogeneous and symmetric, no intramural gas. Response to treatment is rapid (symptom improvement in 48-72 hours with antibiotics).
Criteria
Intramural gas in bladder wall; 60-70% in diabetic patients; gas-forming organisms; intramural ± intraluminal gas on CT; mortality 7-14%; IV antibiotics + bladder decompression mandatory.
Distinct Features
Pathognomonic intramural gas on CT. Perivesical gas extension indicates poor prognosis. Risk of progression to necrotizing cystitis and bladder perforation.
Criteria
Widespread hemorrhage in bladder wall; cyclophosphamide, radiotherapy, BK virus, adenovirus; macroscopic hematuria; wall thickening + intraluminal hyperdense clot (60-80 HU) on CT; T1 hyperintense areas on MRI.
Distinct Features
Intraluminal clot appears hyperdense (60-80 HU) on non-contrast CT — differentiation from stone is important (stone >200 HU). MESNA prophylaxis is standard treatment for cyclophosphamide-related form.
Criteria
Chronic pelvic pain + urinary frequency; non-infectious; 5-10x more common in women; decreased bladder capacity (<350 mL); small-volume, thick-walled bladder; Hunner's ulcers or glomerulations on cystoscopy.
Distinct Features
Bladder volume is small (due to chronic fibrosis), perivesical fat stranding is usually absent. Fibrotic changes (low T2 signal) may be seen on MRI.
Distinguishing Feature
Urothelial carcinoma usually appears as focal asymmetric wall thickening/mass; cystitis is diffuse and symmetric. Carcinoma shows early arterial enhancement; cystitis shows mucosal enhancement. Muscle layer disruption on VI-RADS MRI supports carcinoma.
Distinguishing Feature
Radiation cystitis is associated with pelvic radiotherapy history; wall thickening may be confined to the radiation field; in chronic form, wall may be fibrotic and calcified.
Distinguishing Feature
Neurogenic bladder develops on background of spinal cord injury; trabeculation and thick wall are due to chronic denervation, acute inflammatory findings are absent.
Distinguishing Feature
Bladder fistula creates gas and wall thickening in the bladder lumen — may mimic emphysematous cystitis. In fistula, gas source is from bowel and the fistula tract can be demonstrated on CT.
Urgency
urgentManagement
medicalBiopsy
Not NeededFollow-up
specialist-referralAcute bacterial cystitis is managed with empiric antibiotic therapy; urine culture and sensitivity testing is required in complicated cases. Emphysematous cystitis requires emergent intervention: broad-spectrum IV antibiotics + bladder decompression; if non-responsive, surgical debridement — mortality is 7-14%. In hemorrhagic cystitis, bladder irrigation is performed; if uncontrolled, hyperbaric oxygen or intravesical instillation is considered. Interstitial cystitis requires multidisciplinary approach: behavioral therapy, oral amitriptyline/pentosan polysulfate, intravesical DMSO instillation, sacral neuromodulation. In recurrent cystitis, underlying risk factors should be investigated.
Cystitis is the most common urinary infection. It is much more frequent in women (short urethra). Simple cystitis is treated with antibiotics. Emphysematous cystitis is an emergency requiring broad-spectrum antibiotics and sometimes surgery. In complicated or recurrent cystitis, underlying pathology (obstruction, stone, tumor) should be investigated. Chronic cystitis can reduce bladder capacity, and interstitial cystitis can cause chronic pelvic pain syndrome.