11.4: Radiologic approach to lesions (a systematic approach to clinical scenarios/radiological abnormality)

Suriyaprakash Nagarajan, Rupa Renganathan, Suhasini Balasubramaniam, Anupama Chandrasekharan, Kumarsampath Sumeena

11.4.1

OVARIAN CYST VERSUS BLADDER

Cystic lesions are common in female pelvis and mostly they originate from ovary. Ovarian cysts can arise from epithelial, stromal or germ cell components and can be benign or malignant cystic lesions. Pelvic Ultrasonography (USG) is the preferred imaging modality for evaluation of adnexal cystic lesions. Large simple ovarian cyst appears unilocular, anechoic with thin smooth walls. Such large simple cysts are confused with distended bladder. Distended bladder is a condition in which the urinary bladder is full and the patient is unable to void completely causing abdominal discomfort and pain. Distended bladder can be due to obstruction to passage of urine, neurological disorder or spastic sphincter.

Differential diagnosis of cystic lesions in pelvis can be intraperitoneal, extraperitoneal and both intraperitoneal and extraperitoneal. Cystic lesions of intraperitoneal origin includes peritoneal inclusion cyst, paraovarian cyst, mucocele of appendix and hydrosalpinx. It is important to differentiate large simple ovarian cyst and distended bladder when patient presents with lower abdomen pain and the patient’s clinical history helps to make an accurate diagnosis (Table 11.4.1.1).

TABLE 11.4.1.1

Differentiating Points Between Ovarian Cyst and Distended Bladder

Ovarian Cyst	Distended Bladder
Ovarian cyst in plain radiograph is noted on one side of the pelvis. Areas of calcification can be demonstrated.	Plain radiograph (Fig. 11.4.1.1) shows a midline opacity arising from the pelvis extending above the pubic symphysis which gets relieved on catherization.
Ipsilateral ovary not seen separately from the lesion (Phantom sign) or the cyst is seen to arise from within the ovary (embedded organ sign).	Ovaries can be demonstrated separate from the distended bladder.
Complete or incomplete septae often seen (Fig. 11.4.1.2A).	Septations are not seen in distended bladder. In long-standing bladder distension there is significant amount of debris, moving with the movement of the patient.
Ovarian cysts are anechoic lesions noted on one side of pelvis (Fig. 11.4.1.2B). Normal ovarian stroma can be seen around the cysts in case of small cysts.	Bladder is visualized as a round or oval shaped anechoic fluid filled structure in the midline of pelvis (Fig. 11.4.1.3A).
Colour Doppler shows vascularity in the septum (Fig. 11.4.1.2C).	Ultrasonography shows distal ureteral jet. Doppler imaging shows the stream of urine entering the bladder through the ureteral orifice (Fig. 11.4.1.3B).
No evidence of trabeculations in cyst wall.	Distension of bladder due to neurological conditions shows trabeculation in bladder wall.
Solid components more commonly seen (Fig. 11.4.1.2D).	Solid components not usually seen in distended bladder.

Fig. 11.4.1.1 Plain radiograph showing soft tissue opacity in the midline of pelvis (marked in yellow colour) – distended bladder.

Fig. 11.4.1.2 Ultrasonogram showing septations within the cyst (A), anechoic cyst without septation (B), septal vascularity (C) and soft tissue component with vascularity (D).

Fig. 11.4.1.3 USG shows anenchoic fluid-filled structure in the midline of pelvis. Ureteric jet visualized in grey scale (arrow) and colour Doppler (arrowhead) imaging.

11.4.2

UTERINE VERSUS EXTRAUTERINE MASS

Imaging approach

Ultrasound is usually the initial imaging modality for the pelvic mass. When USG findings are indeterminate to ascertain the organ of origin and to characterize, the next imaging modality is MRI due to its superior soft tissue resolution and multiplanar imaging capability (Figs. 11.4.2.1 and 11.4.2.2). Signs are demonstrated in Figs. 11.4.2.3 to 11.4.2.6.

Fig. 11.4.2.1 Imaging differential diagnosis of pelvic masses.

Fig. 11.4.2.2 Stepwise imaging approach for diagnosis and characterization.

Fig. 11.4.2.3 A 53-year-old female with large abdominopelvic mass lesion on USG. T2-weighted MRI images of pelvis. Figure B demonstrates **Localization:** Both the ovaries are seen separate from the mass (black arrows). Claw sign – the mass was seen attached to the left lateral wall of uterus with uterine parenchyma draping around its base (arrowheads). Bridging vessel sign – multiple vessels are seen as flow voids traversing from the uterine wall into the mass (white arrows). **Characterization:** The lesion is solid and has predominantly T2 hypointense signal with cystic degeneration. **Probable diagnosis:** Uterine fibroid with cystic degeneration. **Final diagnosis:** Uterine fibroid with cystic degeneration.

Fig. 11.4.2.4 A 33-year-old female with indeterminate mass on USG. **Localization:** Both the uterus (star) and the right ovary (arrow) are seen separately from the mass. **Ovarian beak sign:** There is splaying of the left ovarian parenchyma around the inferior surface of the mass (white arrows). ***Draining vessel sign:*** Left gonadal vein is seen draining the mass shown on sagittal post gadolinium image (arrowheads). **Characterization:** The lesion is solid and has predominantly T2 hypointense signal with heterogeneous enhancement on delayed images. **Probable diagnosis:** solid lesion left ovarian lesion with T2 hypointensity likely fibroma/thecoma. **Final diagnosis:** Benign sex cord stromal tumour – fibroma.

Fig. 11.4.2.5 A 77-year-old postmenopausal female with indeterminate mass in pouch of Douglas on USG. **Localization:** There is a dumb-bell-shaped mass in the pouch of Douglas with unclear/lost interface with the posterior uterine wall (arrow) and intraluminal rectal component (star). DWI: The lesion is clearly seen to be separate from the uterus on DWI image. The lost fat plane on T2 image is due to oedema in the peritumoral fat. **Characterization:** The lesion is solid and has hyperintense signal on T2. **Probable diagnosis:** Rectal carcinoma. **Final diagnosis:** Rectal carcinoma.

Fig. 11.4.2.6 A 25-year-old female with indeterminate right adnexal lesion on USG. **Localization:** Both the ovaries and the uterus (black star) are seen separate from the mass. The mass lies in presacral space displacing the rectum towards left and anteriorly (white star). **Characterization:** The lesion is cystic with nodular enhancement at the periphery (arrow). No fat/calcification was seen on CT (not shown here). No bony erosions/intra foraminal extension is noted. **Probable diagnosis:** Presacral cystic tumour likely schwannoma with cystic degeneration. **Final diagnosis:** Schwannoma.

The sequences used in MRI pelvis are conventional T2WI in all three planes and T1WI in single plane. The problem-solving sequences are oblique coronal and oblique axial T2 along and perpendicular to the long axis of uterus in sagittal localizer. It can identify the organ of origin. Other sequences like T1 fat sat, diffusion-weighted imaging (DWI) and dynamic contrast T1WI with fat sat and subtracted images help to characterize the lesion further.

11.4.3

BLADDER MASS VERSUS PROSTATE MASS

Irregular mass lesions in the bladder neck are termed as ‘Bladder occupying lesions’. It is often difficult to determine whether the origin of these lesions is the bladder or the prostate gland.

Transabdominal Ultrasound with colour Doppler studies and CT imaging do not usually delineate the origin of the lesions.

The following features may aid in the differentiation (Table 11.4.3.1):

• Mass lesion in the inferior and posteroinferior bladder wall in an elderly male should be suspected to be of prostatic origin
• Hence digital rectal examination and serum prostate specific antigen assay should be performed
• Transrectal ultrasound examination should be done if indicated by the results of DRE and PSA
• Based on the inferences of TRUS, MRI of the prostate gland or TRUS-guided biopsy is performed
• 11C ACE based PET CT scan helps to confirm tumours of prostatic origin
• Loss of prostate symmetry, disruption of the capsule and distortion of the anatomical structure are important to determine the prostatic origin of the mass
• Prostatic malignancies arising from the peripheral and transitional zones and presenting as bladder occupying lesions are diagnosed to a greater degree by TRUS biopsy and TRUS-guided biopsy
• Prostatic masses arising from the central zone are more prone to invade the bladder neck and to metastasize early
• Multifocal lesions within the bladder suggest that the infiltrating mass is a bladder lesion
• Subtle upwardly directed bladder wall at bladder–prostate interface, suggests that the mass is of prostate origin and vice versa
• PET CT in bladder occupying lesions requires the use of 11C ACE PET/11C Methionine/11C Choline as it gets metabolized in the pancreas and hence radioactivity in the bladder can be avoided. The utility of PET CT is to demonstrate additional lesions in the urinary tract which favours bladder origin of the mass
• DCE MRI shows early enhancement of bladder and prostate masses and hence cannot help to differentiate between tumour of bladder

TABLE 11.4.3.1

Differentiating Bladder Neck Mass and Prostate Mass

S. No.	Feature	Bladder Neck Mass	Prostate Mass
1	History	Painless haematuria	Usually asymptomatic
2	Investigations	TAS, TRUS, MRI, Cystoscopy-guided biopsy	PSA, DRE, TRUS, MRI, TRUS-guided biopsy
2	At what point is the cross over between the two lesions	T4 bladder cancer invading the prostate	Aggressive prostate cancer protruding into the bladder
3	Epicenter of the lesion	Within the bladder	Within the prostate gland
4	Central necrosis in the mass	Not commonly seen	Seen in sarcomas
5	IVU/CT urography	Additional lesions in the urinary tract suggest that the bladder occupying mass in the bladder neck is of bladder-origin	Prostate masses do not commonly cause masses in the urinary tract except for the very rare metastasis
7	Virtual cystoscopy	Additional lesions in the bladder wall and dome suggest that the bladder occupying mass in the bladder neck is of bladder-origin
8	MRI T2 hypointensity	Bladder masses are usually T2 hyperintense	Seen in adenocarcinomas
9	MRI T2 hyperintensity	Bladder masses are usually T2 hyperintense	Urothelial tumours infiltrating the prostate, neuroendocrine masses
10	MRI T1 and T2 hyperintensity	Bladder masses are usually T1 hypointense and T2 hyperintense	Mucinous adenocarcinoma
11	MRS	Elevated choline values are seen in highly cellular masses	Elevated choline:citrate ratio in prostate malignancies No significant finding in mucinous adenocarcinoma
12	DWI	Diffusion restriction is seen in malignant bladder masses	No restriction in mucinous adenocarcinoma
13	BPH versus bladder mass		Exophytic BPH has signal intensities and appearance similar to and is contiguous with BPH within the gland

Fig. 11.4.3.1Irregular hypoechoic lesion arising from the posterior wall. Separate fat plane seen between prostate and the mass (yellow arrow).

Fig. 11.4.3.2Large irregular isoechoic hanging bladder mass from right lateral wall of the urinary bladder.

Fig. 11.4.3.3Enlarged prostate with intravesicle enlargement of median lobe.

11.4.4

OVARIAN MASS VERSUS PARAOVARIAN MASS

Ultrasonography (USG) is the primary imaging modality in patients presenting with pelvic symptoms. Transvaginal, transabdominal or both should be performed in evaluation of such patients to differentiate ovarian and nonovarian origin of the lesions. Ovarian lesions can be a simple ovarian cyst, complex cyst with septations and solid components or a solid mass. Paraovarian lesions are remnants of the Wolffian duct in the mesosalpinx along fallopian tube or the ovaries and do not arise from the ovary. Paraovarian cysts are classified based on their site of origin into paratubal mesosalpingeal cysts, hydatid cysts of Morgagni, paraovarian cystadenoma and subserosal cysts. Differentiation of ovarian and paraovarian lesion poses significant diagnostic challenge. Both Computed tomography (CT) and Magnetic resonance imaging (MRI) are essential problem-solving tool in determining the site of origin of a pelvic mass.

The first step in pelvic mass evaluation is to find out if it is ovarian or nonovarian in origin. Characterization of paraovarian or ovarian lesions is of utmost importance in order to optimize therapeutic procedures and it influences patients management (Figs. 11.4.4.1 and 11.4.4.2). Findings such as ovarian vascular pedicle sign, claw sign, bird beak sign and visualization of normal ovary helps to differentiate between ovarian and paraovarian lesions. Subsequently ovarian lesions should be categorized into benign, indeterminate and malignant masses (Table 11.4.4.1).