Sonography of tumors and tumor-like lesions that mimic carcinoma of the urinary bladder.

One of the basic abdominal organs that is assessed during transabdominal ultrasound examination for urological reasons is the urinary bladder. The bladder must be filled with urine. This is a prerequisite for a reliable assessment and, at the same time, an acoustic window in examining adjacent structures and organs, for instance the prostate gland. In some cases, doubts occur with respect to the nature of lesions detected. The paper presents anatomic lesions, defects and pathologies which might be erroneously interpreted as tumors of the urinary bladder, i.e. transitional cell carcinoma of the urinary bladder. The following lesions are discussed: 1) anatomic defects (including urachus remnants, ligaments that stabilize the bladder or cyst in the opening of the ureter into the bladder - ureterocele); 2) tumor- like lesions in the lumen of the urinary bladder (such as blood clots, fungus balls, stones or foreign bodies); 3) bladder wall pathologies (i.e. cystitis or endometriosis), focal decidual transformation of stromal cells or inflammatory pseudotumor; 4) lesions impressing on the bladder from the outside (the mesentery of the sigmoid colon, the bowel, pathological lesions in organs adjacent to the urinary bladder, inflammatory infiltration, vasogenic compression of the bladder, pelvic lipomatosis, pathological lesions of the pubic symphysis); 5) postoperative lesions. All these lesions may mimic carcinoma of the urinary bladder in sonography. Bearing this fact in mind is significant in establishing a diagnosis. Due to the malignant character of carcinoma of the urinary bladder and the need for aggressive surgical treatment, a correct diagnosis of this disease is essential for patients, particularly because the lack of adequate treatment and delayed treatment considerably affect prognosis.

One of the basic abdominal organs that is assessed during transabdominal ultrasound (US) examination for urological reasons is the urinary bladder. The bladder must be filled with urine. This is a prerequisite for a reliable assessment and, at the same time, an acoustic window in examining adjacent structures and organs, for instance the prostate gland. Sonography enables detection of 95% of exophytic lesions within the urinary bladder with the diameter exceeding 5 mm. In the great majority of cases, it is carcinoma of the urinary bladder (98%)(. Due to its malignant character and the need for aggressive surgical treatment, a correct diagnosis of this disease is essential for patients, particularly because the lack of adequate treatment and delayed treatment considerably affect prognosis(. For the purposes of this paper, lesions mimicking carcinoma of the urinary bladder have been classified in the following way:

Anatomic defects:

Urachus remnants

Ligaments that stabilize the bladder

Ureterocele

Tumor-like lesions in the lumen of the urinary bladder:

Blood clots

Fungus balls

Stones

Foreign bodies

Bladder wall pathologies:

Cystitis

Endometriosis

Focal decidual transformation of stromal cells

Inflammatory pseudotumor

Lesions impressing on the bladder from the outside:

Mesentery of the sigmoid colon

Bowel

Pathological lesions in organs adjacent to the urinary bladder

Inflammatory infiltration

Vasogenic compression of the bladder

Pelvic lipomatosis

Pathological lesions of the pubic symphysis

Other lesions bulging into the lumen of the urinary bladder

Postoperative lesions.

1. Anatomic defects as causes of false diagnoses of urinary bladder carcinoma

1.1. Urachus remnants

Following the end of the fetal life, the urachus normally undergoes complete closure and transforms into a band of connective tissue that runs from the apex of the urinary bladder and forms the median umbilical ligament. The urachal remnant may be visible in a US examination in the apex of the bladder as a solid tumor-like lesion within the detrusor muscle (87% of cases) (fig. 1). Sometimes it forms a duct, which is a sign of preserved patency. If only a fragment that communicates with the bladder is preserved, a diverticulum is formed. If, however, the patency of the whole urachus is preserved, a fistula develops which manifests itself with periodic leakage of pus or urine (49%)( (fig. 2). The mean size of these two urachal forms amounts to approximately 13.5 × 12.6 × 5.2 mm(. Their echogenicity is similar or greater than that of the adjacent urinary bladder. The frequency of occurrence decreases with age: in patients below 16 years of age, the urachal remnant is diagnosed in 61.7% patients and in patients above 56 years of age – only in 3.7%(. Rarely, a malignant transformation (adenocarcinoma or sarcoma) may take place within the urachal remnant. Adenocarcinoma develops from the involuted urachus in approximately 1/5 million cases. This type of carcinoma accounts for 1–2% of all cancerous lesions within the urinary bladder(. Adenocarcinoma that originates from the urachus has a more favorable prognosis than carcinomas developing in other fragments of the urinary bladder wall(. It is usually larger than typical adenocarcinoma of the urinary bladder and is characterized by heterogeneous echostructure. Frequently, it contains calcifications and usually pathological blood flow can be visualized(.

Fig. 1

In two planes, arrows indicate a nodular form of the involuted urachus

Fig. 2

In two planes, arrows indicate a ductal form of the involuted urachus

A urachal cyst at the level of the space of Retzius gives a typical image of an anechoic lesion that impresses on the anterior wall of the bladder to the degree that depends on the size of the cyst (fig. 3). Occasionally, it may become infected and then, its contents become echogenic to varying degrees. Sometimes, patients may manifest symptoms of inflammatory infiltration of the bladder wall and anterior abdominal wall. Bleeding to the cyst or formation of concrements within it have also been reported. Such a cyst needs to be differentiated from a diverticulum in the same localization which is also associated with incomplete regression of the urachus. In such a situation, it is possible to observe a connection between the diverticulum and the bladder. Moreover, it is usually possible to observe the change in the size (filling) of the bladder during micturition (fig. 4)(.

Fig. 3

Cyst of the urachus bulges into the apex of the urinary bladder (arrow)

Fig. 4

In the apex of the urinary bladder, a small diverticulum is visualized as the urachal remnant

1.2. Ligaments that stabilize the bladder

The ligaments that stabilize the bladder frequently cause erroneous diagnoses of pathological lesions during US examinations of the urinary bladder. In women, this concerns the symmetrical pubovesical ligaments which transform into the vesicouterine ligaments; in men, however, this concerns pubo-vesico-prostatic and rectovesical ligaments(. These structures are clearly visible, particularly when the urinary bladder is poorly filled. Despite their bilateral localization (fig. 5), they are most frequently manifested on the right side (fig. 6), which sometimes causes its erroneous interpretation as a pathological lesion. They are rarely seen on the left side (fig. 7). According to our unpublished US examinations conducted in 830 persons, sonographic criteria for the above- mentioned ligaments are as follows:

Fig. 5

Bilateral compression of the urinary bladder wall by the pubovesical ligaments (arrows) mimicking pathological lesions – transverse plane

Fig. 6

In two planes, the pubovesical ligament mimics a tumor of the bladder on the right wall (arrows)

Fig. 7

Pubovesical ligament mimics a tumor on the left wall of the urinary bladder (transverse plane)

parallel course in the form of a hyperechoic band surrounding the urinary bladder;

tumor-like lesions, usually on the right side;

no signs of flow during Doppler examinations;

occurrence when the bladder is not fully filled and usually, disappearance when it is well-filled;

diagnosing them in both men and women with similar frequency.

1.3. Ureterocele

Ureterocele forms a thin-walled structure with various sizes that contains urine and bulges into the lumen of the urinary bladder. A characteristic feature of this cyst is its changing size in the course the examination connected with inflow and outflow of urine from the opening of the ureter into the bladder (figs. 8, 9). Ureterocele may accompany renal duplication(. It may also coexists with vesicoureteral reflux(. In this case, it concerns the ectopically localized (lower and more medially) ureter opening of the upper segment of the duplicated kidney. The volume of the cyst may be additionally complicated by narrowing of the opening or stones. Ureterocele should be differentiated from mild forms of megaureter(. Due to its bulging towards the neck of the urinary bladder, this lesion may occasionally cause difficulties in passing urine such as excessive residual urine following voiding and in extreme cases, even urinary retention(.

Fig. 8

Ureterocele captured in two phases: emptied and filled with urine (arrows)

Fig. 9

Ureterocele. Color Doppler captured the moment of urine inflow into the cyst

2. Tumor-like lesions in the lumen of the urinary bladder

2.1. Blood clots in the urinary bladder usually form echogenic masses without acoustic shadow and without visible blood flow in Doppler examination (fig. 10). They usually move when the patient changes position. Large blood clots are oval and may occupy the entire lumen of the bladder. The diagnosis of a blood clot may be indicated by hematuria after renal trauma or bladder injury and by the condition after transurethral procedures, partial renal resection and percutaneous nephrolithotripsy (PCNL). In the case of large lesions and unsure diagnosis, the bladder may be rinsed after a catheter is introduced. Spontaneous evacuation of large clots is very slow and burdened with a risk of complications, such as infection or urinary retention. Follow-up examinations will show slow reduction of the lesion until its complete resolution(.

Fig. 10

After electroresection of the prostate. Arrows point to two blood clots in the fundus of the urinary bladder

2.2. Fungal masses in the form of round formations are sometimes visible in the bladder (fig. 11). This is true mainly for patients with uncontrolled diabetes, chronic urinary tract infections as well as immunocompromised patients, those catheterized for a long time and those treated with antibiotics and corticosteroids. Such lesions are usually caused by Candida albicans infection and resemble blood clots – they are movable with the change of the patient's position(.

Fig. 11

Fungal ball in the urinary bladder (vertical arrow). On the left, the arrow points to a small stone in the diverticulum

2.3. Vesical stones that do not move due to inflammatory reaction of the bladder wall (hanging bladder stones) mimic calcified tumors( (fig. 12). On the other hand, in transitional cell carcinoma (TCC), which develops in the bladder for a long time, incrustation may occur on the surface of the villi, which relatively frequently mimics stones in the US examination. Unmovable deposits may also be localized in the ureter opening into the bladder or in ureterocele. Another example of an unmovable stone is incrustation resulting from erosion of the tape used in treating stress urinary incontinence in women or disorders of pelvic wall statics. In such cases, it is typically localized within the trigone of the bladder. An additional diagnostic problem is posed by considerable urinary urges which result in the inability to hold larger amounts of urine in the bladder. In the case of doubts, it is advisable to perform a pelvic X-ray. Transvaginal sonography is also helpful – this method enables to thoroughly trace the localization of the tape and visualize stones or other lesions within the trigone of the urinary bladder provided that the bladder is filled properly.

Fig. 12

Stone (arrow) fixed to the wall of the urinary bladder mimics a proliferative lesion

2.4. Foreign bodies in the urinary bladder are rarely encountered. They are usually fragments of catheters, sutures or damaged elements of endoscopic equipment(; sometimes these are objects used for masturbation, such as a pencil or thermometer, and foreign bodies after gunshot wounds and other injuries(. The presence of an intrauterine device that perforated the uterine wall has also been reported(. The presentation of foreign bodies is diverse. They frequently mimic calcified pathological masses. In the majority of cases abdominal X-ray is decisive.

3. Tumor-like lesions associated with the wall of the bladder

3.1. Cystitis cannot be definitively differentiated from cancerous lesions based on sonography irrespective or its manifestation (whether it manifests as thickening of the bladder wall or presence of exophytic lesions) (fig. 13). A typical example is the image of inflammatory lesions after catheterization, which poses problems with interpretation even during endoscopy – the only reliable diagnostic criterion is the result of a histopathological examination of a sample collected during cystoscopy. The US image usually presents generalized thickening of the bladder walls (fig. 14) and decrease in its volume. In such a case, neoplastic or inflammatory etiology must be excluded in the first place(.

Fig. 13

In the fundus of the urinary bladder, arrows point to lesions in the course of glandular cystitis which were previously interpreted as papillomas

Fig. 14

Fifty-six-year-old woman with chronic cystitis controlled cystoscopically for years – difficult to differentiate from cancerous lesions. Arrows point to thickened fragments of the urinary bladder wall

3.2. Endometriosis in the urinary bladder belongs to the most common localizations of this disease in the urinary tract. Its occurrence in the bladder may be idiopathic or secondary to surgeries of the pelvic organs. Symptoms associated with the menstrual cycle, pain and, more rarely, hematuria are present in only 40% of women. Endometriosis is typically localized in the vesicouterine pouch and grows into the bladder from the outside (fig. 15). It rarely creates polyp formations. Lesions in the urinary bladder frequently occur together with foci in the pelvis minor. They are most clearly visible in a transvaginal US examination and in magnetic resonance imaging in T1-weighted images with or without fat suppression – they demonstrate the presence of hemoglobin and its metabo-lites in the focus assessed. The final diagnosis is determined on the basis of histopathological examinations(.

Fig. 15

Endometrial infiltration of the posterior wall of the urinary bladder following cesarean section (arrows) in a 31-year-old woman

3.3. Focal decidual transformation of stromal cells (deciduosis) is a particular type of lesions. In may develop in the urinary bladder of pregnant patients and resolves following labor. It is a diagnostic challenge since in this period, the following may also appear: urothelial carcinoma, leiomyoma or leiomyosarcoma, inflammatory pseudotumor, rhabdomyosarcoma and fibroma. A definitive diagnosis is obtained based on the result of a histopathological analysis(.

3.4. An inflammatory pseudotumor is a rare lesion of unknown etiology. It is encountered in various organs: lungs, pancreas, liver, stomach, spleen and occasionally also in the urinary bladder. It is benign and originates form the mesenchyme but is frequently interpreted as a malignant mass due to dysuria and hematuria. The tumor usually grows towards the lumen of the bladder (an exophytic tumor) but may also be localized intramurally, mainly in the fundus and lateral walls (fig. 16). The only reliable diagnostic method is a histopathological examination which reveals the presence of myofibroblasts, although even in this case, the differentiation with embryonal rhabdomyosarcoma is still problematic. This type of tumors usually occurs in adolescence, predominantly in female patients – 3 to 1(.

Fig. 16

Extensive lesions of the urinary bladder with considerable volume reduction due to infiltration of the inflammatory pseudotumor in a 13-year-old boy

4. Lesions bulging into the lumen of the urinary bladder

4.1. The mesentery of the sigmoid colon folded in the transverse axis may compress the posterior wall of the urinary bladder to the degree depending on its filling, particularly when the mesentery is extended and infiltrated with fat. A tumor-like lesion is observed particularly when the bladder is poorly filled with urine (fig. 17). Sometimes, vessels may be visualized within this structure. If doubts occur, the US examination should be repeated when the bladder is filled – then the compression of the mesentery will disappear or become flatter. The aforementioned situation with the effect of the mass made up by the mesentery that is extended or infiltrated with fat has not been noted in the literature so far.

Fig. 17

Two planes of a pseudotumor of the urinary bladder caused by compression of the mesentery (arrows). S – gas in the sigmoid colon

4.2. The intestine, particularly filled with fecal contents, may pose a similar diagnostic problem and also compress the posterior wall or the apex of the urinary bladder (fig. 18). Sometimes, the small intestine in women positions itself in the vesicouterine pouch (fig. 19). The identification of peristalsis in the observed lesion facilitates an accurate diagnosis. As for the large bowel, doubts are resolved upon a repeated examination, particularly when the bowel is empty.

Fig. 18

Tumor-like compression of the apex of the urinary bladder by the intestinal loop filled with contents (arrows)

Fig. 19

Small intestine localized in the vesico-uterine pouch compresses the apex of the urinary bladder posteriorly (arrows). U – uterus, B – urinary bladder

4.3. Pathological lesions in organs adjacent to the urinary bladder

4.3.1. Inflammatory infiltration of the pelvic organs and the urinary bladder usually concerns patients with sigmoid colon diverticulosis and inflammatory lesions of the small intestine in the course of Crohn's disease or, sometimes, with inflammation of the reproductive organ. Sometimes, abscesses or vesicointestinal fistulae develop.

A characteristic symptom may be the presence of gas bubbles in the bladder or during voiding in the interview. Sonographic assessment of the pelvic organs with the use of endorectal or endovaginal transducers allows a correct diagnosis to be established (figs. 20, 21).

Fig. 20

Thirty-six-year-old patient with perforation of the sigmoid colon diverticulum and a tumor-like infiltration of the posterior wall of the urinary bladder (arrow). B – urinary bladder, S – sigmoid colon

Fig. 21

Extensive infiltration with hyperemia of the posterior wall of the urinary bladder in a 26-year-old woman with Crohn's disease

4.3.2. Lesions in the pelvic organs may mimic a pathological process originating from the urinary bladder. This particularly concerns the external iliac arteries which become visibly extended and kinking in advanced athero-sclerosis. They impress on the urinary bladder, particularly when an aneurysm is also present. In the narrow pelvis, even normal arteries might cause a similar morphological effect (fig. 22). A differential diagnosis is based on Doppler examinations.

Fig. 22

External iliac arteries bilaterally compress the lateral walls of the urinary bladder, which was confirmed in a color Doppler examination

4.3.3. Pelvic lipomatosis is a disease entity distinguished from pseudotumoral abdominal lipomatosis and causes mainly urological problems. The deposited fat in the pelvis minor surrounds and impresses on the organs, mainly on the urinary bladder and rectum. As a result, the urinary bladder becomes deformed and cigar-shaped. As a consequence of decreased volume, lower urinary tract symptoms (LUTS) develop (fig. 23A, B). Sometimes, these lesions are so intensified that they narrow the ureters and cause urinary retention in the upper respiratory tract(. Moreover, it should be remembered that lipomatosis pelvis is relatively frequently accompanied by cystitis glandularis (glandular cystitis). Therefore, the detection of one lesion should suggest searching for another localization(. Computed tomography and magnetic resonance imaging play the main role in the differential diagnosis(.

Fig. 23A

Echogenic mass bulges into the urinary bladder posteriorly due to pelvic lipomatosis (transverse plane)

Fig. 23B

The same lesions as in fig. 23A in the sagittal plane

4.3.4. Degenerative lesions of the pubic symphysis may rarely mimic tumors of the urinary bladder. The first authors to indicate this problem were Sudoł-Szopinska et al. ( Such a situation may occur when the lesion is located directly behind the symphysis, i.e. on the anterior wall of the bladder in the median line (fig. 24). In a cystoscopic examination, the image resembles that of submucosal tumors (leiomyoma, hemangiopericytoma, pheochromocytoma, paraganglioma and others). The decisive examination is computed tomography or magnetic resonance imaging in combination with the negative result of a histopathological examination of the sample collected during cystoscopy.

Fig. 24

In two planes, a hypertrophic pubic syndesmosis mimics a tumor on the anterior wall of the urinary bladder

4.3.5. Other lesions in the pelvis may also cause an erroneous diagnosis of urinary bladder tumors. They are frequently mimicked by uterine myomas, central zone of the prostate gland or enlarged pelvic lymph nodes (fig. 25). The identification of the central zone that bulges into the lumen of the urinary bladder does not usually pose diagnostic problems for ultrasonographers. During the examination, the patient's bladder needs to be well-filled. In some cases of an atypical image of the central zone, it is helpful to perform TRUS examination – transrectal ultrasound examination – of the prostate gland. This very clearly shows the continuity of the structure observed, the echogenicity of which resembles that of the prostate.

Fig. 25

Tumor-like compression of the bladder by enlarged lymph nodes (N) in the course of infectious mononucleosis

5. Postoperative lesions

Numerous laparotomic, laparoscopic and endoscopic procedures conducted within the lower urinary tract and pelvis minor may sometimes cause diagnostic problems as well. Early complications include a hematoma, intramural abscess of the urinary bladder, blood clots and foreign bodies in the bladder. Delayed complications may include granulomas that form around sutures or tape stabilizing the bladder (fig. 26)(. Teflon or collagen injected intramurally in the region of the ureter opening into the bladder, which is performed in treating vesicoureteral reflux, may also cause an image of a tumor-like lesion (fig. 27). A real challenge for an ultrasonographer is to assess the intestinal orthotopic neobladder which is created after radical cystectomy. It may be made of the small or large intestine, or from both of them simultaneously. In the ultrasound examination, it has uneven internal outlines due to hypertrophic intestinal folds (fig. 28). Additionally, mucus may be visible in its lumen. A factor that facilitates correct interpretation is usually active contractibility during the examination which indicates the lack of wall infiltration.

Fig. 26

Granuloma in the urinary bladder that developed around a suture following sling placement

Fig. 27

Masses of plastic injected into the region of the ureteral opening in the treatment of reflux nephropathy cause colored twinkling artefacts

Fig. 28

Artificial urinary bladder created from the small intestine. It has uneven internal outline due to thickened folds of the mucus membrane (arrows)

The paper has not mentioned numerous pelvic neoplasms that may infiltrate the urinary bladder and also pose a diagnostic challenge in determining the origin of the lesion. The difficulties discussed above sometimes require the usage of various imaging methods, such as US examination with the use of endocavitary transducers, cystoscopy, computed tomography, magnetic resonance imaging or colonoscopy. Finally, in order to verify imaging findings, patients are qualified for a cystoscopy during which samples are collected for a histopathological analysis. The ability to properly diagnose a pseudotumor of the urinary bladder in the transabdominal US examination may help avoid expensive imaging examinations and invasive endoscopic diagnosis.

Conclusions

The ultrasound examination of the urinary bladder plays an important role in the diagnosis of the abdominal organs and structures. Although carcinoma is the most commonly diagnosed lesion in the bladder, particularly when hematuria is also present, there also are numerous conditions that may mimic it. Therefore, an ultrasound examination conducted properly with adequate filling of the bladder is a condition necessary for avoiding diagnostic pitfalls(. Carcinoma of the urinary bladder is a dangerous neoplasm that requires active surgical treatment and therefore, each doubt in the diagnosis must be resolved in a histopathological analysis. The only situations in which this principle does not have to be followed is identification of anatomic variants and lesions discussed in points 2 and 5.