Contrast Enhanced Ultrasound of the Scrotum: Techniques

A scrotal CEUS examination is performed with the patient in the supine position, the penis lifted onto the abdomen and covered for privacy. After identifying a scrotal abnormality using initial greyscale ultrasound and CDUS, CEUS is employed. The procedure involves a bolus injection of an ultrasound contrast agent (UCA), administered via a 22-gauge cannula inserted into the antecubital vein.  The most widely used microbubble UCA for the assessment of scrotal disease is Lumason™/SonoVue™ (Bracco SpA, Milan), a sulfur hexafluoride microbubble contrast agent. The examination requires a higher dose of the microbubble UCA (4.8mls of Lumason™/SonoVue™), as the physics of the harmonic response of the microbubble is governed by the acoustic properties in the insonating ultrasound field, with the smaller microbubbles required to interact with the higher frequency beam found at a smaller concentration [8,15].  Harmonic imaging is used with a low mechanical index (MI), typically set at or below 0.10, and a frame rate of 10–20 frames per second during the enhancement phase. The initial CEUS examination, occurring within the first two minutes after injection, is critical for capturing meaningful diagnostic information.

Optimising CEUS Imaging: Technical Tips and Safety Consideration

When performing CEUS, specific technical considerations are essential for optimal imaging. A split-screen approach, displaying B-mode and CEUS images side by side, allowing low-MI B-mode images to localise the area of interest. The focus should be set just deep to the target area, and gain should be adjusted before injecting microbubble UCA. Pre-contrast images should appear nearly black. The dynamic range can be set wide to capture fine differences in enhancement or narrowed to make blood vessels appear brighter. Mechanical index should be carefully managed, as excessively high MI can disrupt microbubbles in the near field, while too low MI results in poor visualisation of the far field. Video clips should always be recorded for re-evaluation. CEUS examinations are safe but require precautions due to the rare risk of anaphylactic reactions, necessitating prompt access to resuscitation equipment.

Absence of Vascularity: Patterns of Diseases

Torsion of the spermatic cord

Spermatic cord torsion most commonly occurs at the onset of puberty and is thought to be associated with the bell clapper deformity. Absence of flow on CDUS is considered the standard diagnostic criterion. However, intermittent torsion may present with normal colour Doppler flow [10]. CEUS conclusively demonstrates areas of infarction, making it particularly valuable in cases of ‘missed’ torsion. when the patient presents days after the acute episode, often with diminished pain and an enlarged, heterogeneous testis. CEUS also offers unique advantages in paediatric populations as it serves as a problem-solving tool in cases of clinically suspected missed torsion when CDUS yields inconclusive results due to apprehensions about suboptimal testicular vascularity assessment in children [11].

Fig 1: Spermatic Cord Torsion. 26-year-old with acute left testicular pain presented after 4 days of pain, B-mode (a) shows normal right testis and an enlarged heterogenous left testis (arrow). The microvascular imaging (b) shows no vascular flow (arrow) and the contrast enhanced ultrasound (c) also demonstrates no vascularity (arrow). The right testis is normally perfused (star). Histology was of infarction and no malignancy, spermatic cord torsion.

Acute segmental Infarction

Segmental testicular infarction is an uncommon, with predisposing factors including epididymo-orchitis, trauma, hypersensitivity angiitis, intimal fibroplasia of the testicular artery, previous surgery, polycythaemia, and sickle cell disease [12,13]. On greyscale ultrasound, the appearance of segmental infarction is variable and may present as areas of mixed or low reflectivity, often wedge-shaped or round, mimicking tumours [12]. CEUS is particularly valuable, as it can conclusively depict infarcted, avascular areas [14,15]. In subacute stages, CEUS may reveal avascular lobules and, in some cases, perilesional rim enhancement [15]. Over time, CEUS may show a progressive reduction in the size of the infarcted lesion, aiding in follow-up evaluation.

Fig 2: Isolated Segmental Infarction. 62-year-old with acute left testicular pain. On B-mode ultrasound (a) there is a single irregular mixed reflective area in the anterior aspect of the left testis (arrow) without any vascularity demonstrated on microvascular imaging (b) (arrow). The contrast enhanced ultrasound examination (c) shows an avascular area with surrounding hyperaemia (small arrows), in keeping with an acute segmental infarction. Some revascularisation is occurring (arrowhead).

Fig 3: Multiple Segmental Infarctions. 39-year-old with a 7-day history of right testicular pain. B-mode ultrasound (a) shows focal areas of mixed reflectivity (arrows) with the colour Doppler (b) demonstrates diminished vascularity (arrows), in areas of low reflectivity and mixed reflectivity. The contrast enhanced ultrasound (c) examination confirms areas of absent enhancement consistent with two areas of segmental infarction (arrows).

Trauma

Scrotal trauma is often associated with sporting injuries or motor vehicle accidents, primarily affecting young men [16]. In cases of testicular trauma, determining the extent of viable testicular tissue is critical for surgical decision-making. Conventional ultrasound techniques often underestimate the extent of injury, making accurate evaluation challenging [17].  CEUS provides a significant advantage by clearly delineating the fracture line between non-enhancing devascularised tissue and the enhancing viable parenchyma [18,19]. This additional information can inform the decision for preserving viable testicular tissue and supporting future fertility prospects [20].

Fig 4: Scrotal Trauma. 17-year-old knocked of a bicycle an sustained injury to the left testis. On the B-mode ultrasound (a), there is a heterogenous left testis, more obvious at the lower aspect (arrow). On the microvascular imaging (b), there is poor flow to this area. The contrast enhanced ultrasound (c) examination demonstrates enhancement to the upper aspect of the testis (arrow) and no flow to an infarcted lower aspect (star).

An isolated intratesticular hematoma may result from trauma or iatrogenic causes, such as a testicular biopsy [21]. However, in cases of trivial or forgotten trauma, haematomas can be mistaken for primary germ cell tumours. CEUS plays a pivotal role in these scenarios by conclusively excluding vascularity within the lesion, enabling serial monitoring to confirm regression and avoiding unnecessary orchidectomy [22].

Fig 5: Scrotal Trauma. 45-year-old underwent sperm retrieval from the left testis for management of infertility, presents with continuing pain following the procedure. The B-mode ultrasound (a) demonstrates a serpiginous low reflective area in the mid aspect of the testis (arrow). On the colour Doppler examination (b), some shunting of blood(arrow) is noted to the lateral aspect of the low reflective area. On the contrast enhanced ultrasound examination (c), the shunt is again noted (arrow) and the area of haematoma formation seen (star).

In traumatic echogenic haematocele, CEUS offers value in differentiating a surrounding avascular haematocoele and identifying testicular parenchymal vascularity [23].

Fig 6: Traumatic Haematocele. B-mode US (a) showed an echogenic haematocele preventing assessment of the tunica albuginea contour. However, CEUS (split screens, CEUS image on the left and the corresponding low MI greyscale image on the right) (b) clearly demonstrated normal testicular enhancement without interruption of the tunica albuginea - excluding testicular infarction or rupture and establishing the diagnosis of a simple haematocele. Note that the haematocele (asterisks) shows no enhancement.

Inflammation

An uncomplicated epididymitis is typically diagnosed clinically without requiring imaging. However, persistent symptoms despite treatment warrant further investigation [23,24].  Severe epididymo-orchitis may lead to abscess formation or, in rare cases, venous infarction. Venous infarction is thought to result from local swelling occluding venous drainage of portions or the entirety of the testis [25].

Fig 7: Slow Perfusion after Epididymitis. 58-year-old with a previous history of epididymo-orchitis two years previously, present with a painful smaller left testis, the side of the previous infection. On B-mode ultrasound (a) the left testis is smaller (volume 7mLs) and low reflective (arrow) in comparison to the right. There is no flow seen with microvascular imaging (b) (arrow). On the ‘spectacle’ view, at 14 seconds following injection of contrast (c), the right testis is enhancing (star) but very faint enhancement is seen on the left (arrow). At 34 seconds (d) there is more enhancement (arrow) but still less than the right testis (star).

Contrast enhanced ultrasound clearly delineates avascular components of necrotic areas either within the testis or within epididymal abscesses [26,27], surrounded by inflamed tissue exhibiting increased enhancement [28].

Fig 8: Testicular Abscess. 29-year-old with severe right sided pain treated for infection, presents with right sided painless lump 6 months later. B-mode ultrasound (a) demonstrates a lobulated partly cystic abnormality in the right testis (arrow) , with microvascular imaging (b) showing vascularity of the solid components (arrow). The contrast enhanced ultrasound examination (c) shows dense enhancement of the internal structures of the lesion (arrow) with some surrounding hyperemia. Histology demonstrated a chronic inflammatory lesion, an abscess, without any malignancy noted.

Fig 9: Epididymal Abscess. 56-year-old with underlying diabetes mellitus, presented with a left sided scrotal mass and pain. On the B-mode ultrasound (a) a 20 x 22 mm mixed reflective mass is present in the epididymis (arrow). The colour Doppler ultrasound (b) shows a lack of vascularity within the abnormality (arrow), with the contrast enhanced ultrasound (c) showing absence of enhancement and vascularity centrally (star) and surrounding hyperemia (arrows). An epididymal abscess was present with reduced symptoms in an immuno-compromised diabetes mellitus patient.

Severe epididymitis can compromise venous drainage from the testis, leading to areas of infarction or, in extreme cases, global venous testicular infarction [29,30]. CEUS plays a critical role in this "end-stage" complication, allowing for timely clinical decision-making and intervention.

Fig 10: Global Venous Infarction. 38-year-old man with gross scrotal swelling and underlying epididymitis, presenting with increasing pain on medical treatment. On B-mode (a), using a curvilinear transducer, there is scrotal wall thickening and no colour Doppler flow seen in either testis (star). On the contrast enhanced ultrasound examination (b), the right testis is infarcted with no enhancement (star), following venous occlusion in the presence of severe epididymitis.

Fig 11: Global Venous Infarction with Arterialisation. 38-year-old man with scrotal swelling and underlying epididymitis, a pyocoele presenting with increasing pain on medical treatment. On B-mode (a), there is scrotal wall thickening and no colour Doppler flow seen in the right testis (star) with increased colour flow in the scrotal wall (arrow). On the contrast enhanced ultrasound examination (b) with split screens (right CEUS; left low MI greyscale), the right testis is infarcted with no enhancement, following venous occlusion in the presence of severe epididymitis. CEUS also demonstrates late arterial flow (arrow) (c: split screens: right CEUS; left low MI greyscale), confirming that venous outflow obstruction is the cause of the infarction.

Complex Cysts and Tumours

Simple testicular cysts are often detected incidentally, typically in males over 40 years of age [31]. Simple cysts appear as anechoic lesions with imperceptible walls and through transmission on ultrasound. While these are usually benign, irregular walls or echogenic debris may raise suspicion for a rare cystic testicular tumour [32]. CEUS could demonstrating a lack of enhancement, differentiating between avascular intra-cystic material, such as clots and debris, and vascular cystic tumours.

Fig 12: Intra-testicular Cyst. 64-year-old with increasing size of right hemi-scrotum, with multiple epididymal cysts and intra-testicular cysts seen. On B-mode (a), the intra-testicular cysts is seen with echogenic material within (arrow), and no demonstrable flow in the echogenic material on colour Doppler flow (b) (arrow). The contrast enhanced ultrasound (c) demonstrated no enhancement (arrow) confirming echogenic debris.

Epidermoid cysts, composed of keratinising, stratified squamous epithelium with a well-defined fibrous wall, represent a subset of complex cysts. These lesions are rare, constituting approximately 1% of testicular masses, and are often asymptomatic, palpable, and detected during routine physical examinations. Their ultrasound appearance varies depending on the maturation, compactness, and quantity of keratin present [33]. Characteristic patterns include an "onion ring" appearance of alternating hyper-echogenicity and hypo-echogenicity, an echogenic mass with dense acoustic shadowing due to calcification, or a target-like mass with a central echogenic area surrounded by a hypoechoic periphery. CEUS consistently demonstrates the avascular nature of these lesions [34,35]. In cases where an epidermoid cyst is strongly suspected based on imaging, testis-sparing enucleation may be an appropriate management option.

Fig 13: Epidermoid Cyst. 19-year-old with history of non-specific pain found on ultrasound (a) to have an incidental lesion in the left testis (arrow) with features suggesting an epidermoid cyst. There is no colour Doppler (b) signal in the lesion (arrow). On the contrast enhanced ultrasound (c) examination there is no vascularity within the lesion (arrow).

While CEUS is highly reliable for assessing scrotal lesions, there are rare exceptions where its ability to demonstrate the lack of enhancement requires careful interpretation. Extensively necrotic lesions may exhibit little to no enhancement due to the absence of vascularity within large areas of tissue death [36].

Fig 14: Infarcted Tumour – Pure Seminoma. 41-year-old with a 48x30mm right testicular mass, which is and avascular infarcted tumour with multiple small vascular satellite lesions. The lesions are of low reflectivity (arrows) and do not demonstrate increased flow on microvascular imaging (a). On CEUS (b) the large lesion is avascular (star), the smaller inferior lesion (arrow) has abnormal enhancement, with increased early arterial enhancement and subsequent rapid washout in keeping with a germ cell tumour. On histology this was a ‘Pure Seminoma’.

Similarly, burnt out tumours, which represent a regressed primary testicular malignancy, may appear as avascular areas on CEUS due to fibrosis and necrosis [37].

Fig 15: Burnt Out Tumour. 46-year-old with and, on the greyscale, ill-defined right testicular mass (star), which is mildly hypoechoic on the greyscale and avascular on the colour Doppler examination (a). On CEUS (b) this lesion demonstrated minimal enhancement (b). This characteristic appearance suggest a previous tumour that has regressed, leaving a distinct radiological signature. A retro-aortic node (arrow) was detected on the staging CT (c).

In such cases, CEUS findings must be interpreted alongside other diagnostic modalities, including serum tumour marker levels and cross-sectional imaging, with biopsies of abnormaly retroperitoneal lymph nodes, to confirm or exclude malignancy [38].

Fig 16: Burnt Out Tumour. Contrast enhanced ultrasound revealed an ill-defined hypovascular scar within the left testis in a patient with an abnormal retroperitoneal lymph node on CT. The retroperitoneal lymph node was subjected to a biopsy under CT guidance. A diagnosis of seminoma was confirmed on histology.