Central Nervous System Ultrasonography

There is one notable exception in the CNS, where US can play a significant role in tumor imaging. During surgery, a sterile sheathed US transducer can be placed directly on the exposed brain or spine to locate or facilitate the approach to a known lesion and minimize damage thereby to adjacent neural tissue (Figure 30G.1).² In addition, US can be used to help ensure that a tumor resection has been complete. Intraoperative US can also be used to assist in the resection of spinal masses,³ including tumors and arteriovenous malformations.⁴

Figure 30G.1

Intraoperative sonogram of a patient with a history of melanoma who was found to have a small superficial mass in the right frontal lobe on CT. At surgery the lesion was not palpable, and US was used to guide biopsy and resection. Note well-defined hypoechoic (more...)

Head and Neck Ultrasonography

Although the role of US imaging inside the skull remains limited, the soft tissues of the head and neck are readily accessible to highresolution US. US has been used to differentiate cystic from solid thyroid nodules, and it can readily depict small thyroid masses. In this regard, US has better resolution in the soft tissues than either nuclear scintigraphy or computed tomography (CT). The ability to identify small lesions can be of particular value in differentiating solitary from multiple nodules, and it makes US an excellent method of evaluating and monitoring patients with a history of thyroid irradiation early in life. In addition, the ability to identify small thyroid masses and to guide percutaneous biopsies makes US the preferred method for finding an occult thyroid cancer in a patient who presents with metastatic disease that is compatible with a thyroid origin.⁵ US can also distinguish adenopathy involving anterior cervical nodes from thyroid masses. Gooding and colleagues have also showed that US is uniquely capable of demonstrating whether or not there is carotid involvement by cervical adenopathy.⁶

Although US is less commonly used in the United States for this purpose than in Europe, a number of studies indicate that it may be useful for staging patients with cancer of the floor of the mouth.^7,8 The relative lack of enthusiasm in the United States for evaluating oral neoplasms with this modality probably reflects the ready availability of CT and magnetic resonance imaging (MRI). US does have the advantage of being a real-time examination, however, and therefore may be of special value in identifying fixation when a tumor invades the tongue, vocal cords, or other normally mobile structures. Other uses for US in the head and neck include the identification of enlarged parathyroid glands in patients with hypercalcemia (Figure 30G.2).⁹ and the evaluation of parotid masses.¹⁰ Regardless of the local availability of CT and MRI scanners, US should be the method of first choice for guiding biopsies in the head and neck in lesions which are accessible. US is cheaper and more readily available than either CT or MR in most institutions. It has extremely high spatial and tissue resolution in superficial areas and provides real-time guidance for biopsies, which can be invaluable when trying to avoid the many large blood vessels in the head and neck region.

Figure 30G.2

Parathyroid adenoma: US study on patient with metastatic breast carcinoma and elevated calcium levels. On a longitudinal (sagittal) section through left thyroid gland (T), note well-defined hypoechoic mass inferior to the thyroid, which is typical of (more...)

Thoracic Ultrasonography

In the thorax, the use of US is usually limited to localizing or characterizing pleural opacities that have been identified previously on radiographs. The ultrasonographer should be capable of differentiating between free and loculated effusions, determining which are amenable to thoracentesis (an effusion with numerous internal septa and locules may require thoracotomy), and finding the optimum site for puncture. Tube insertions for pleural drainage or drug administration and other interventional procedures can also be performed under US guidance.¹¹ Within the effusion itself, US can also demonstrate collapsed lung and differentiate it from consolidation without atelectasis.

Color Doppler imaging can be used to evaluate the veins in the neck, upper thorax, and arms. Thrombosed vessels can be readily differentiated from normal ones or from vessels compressed by extraluminal masses. These imaging abilities are of particular value in the cancer patient who presents with acute or chronic arm swelling. The oncologic population is at risk for upper extremity venous thrombosis from several causes, including direct compression by tumor, paraneoplastic thrombogenic syndromes, and indwelling catheters. Color Doppler US has been shown to be highly accurate for evaluating acute thromboses in the jugular, subclavian, and axillary veins (Figure 30G.3).^12,13 The proximal subclavian and innominate vein and the superior vena cava may be difficult to image with US, however, and may require MRI or contrast venography.

Figure 30G.3

After a left mastectomy and subsequent irradiation, a 55-year-old woman presented with acute onset of severe left arm swelling. Color Doppler imaging revealed extensive thrombosis of left subclavian/brachial venous system. Note arterial flow ( red ) adjacent (more...)

Endoscopic US is another important technical adaptation of sonography. This technique requires the incorporation of a minute transducer into the tip of an endoscope and enables the operator to see tissues that are deep to accessible mucosal surfaces. The technique is being used increasingly, and it is an excellent method for assessing the depth of penetration of esophageal and gastric neoplasms, identifying nearby nodal involvement, and defining the internal characteristics of submucosal masses, both benign and malignant (Figure 30G.4).¹⁴ Endoscopic US may eventually prove to be an essential technique for evaluating the mediastinum of patients who have potential nodal spread to that area, since neither CT nor MRI has proved to be as accurate as once hoped.

Figure 30G.4

Endoscopic sonogram of a patient with weight loss. Thickened gastric folds were noted on an upper GI study. Endoscopic US is suggestive of lymphoma. Note marked thickening of wall of stomach (arrows), with preservation of mucosa. Central ringlike structure (more...)

Breast Ultrasonography

A frequent and durable application of thoracic US is, of course, in breast imaging. US is typically used to differentiate solid from cystic masses. Recent investigations demonstrate that, when used in conjunction with mammography, high-resolution US may increase specificity in differentiating benign and malignant masses and may decrease the number of biopsies needed.¹⁵ (see Chapter 30F). Investigators have also attempted to use Doppler US analysis to differentiate benign from malignant breast masses, but the technique is not yet sufficiently developed to obviate the need for biopsy.¹⁶ Another recent application of US in breast cancer has been to detect adenopathy in the internal mammary lymph node chain.¹⁷ The addition of color Doppler imaging will facilitate identification of the internal mammary vessels as they course beneath the upper anterior ribs and thereby help to define adjacent adenopathy.

Abdominal Ultrasonography

US is often considered to be an adjunctive imaging technique for evaluating the abdomen in the cancer patient. Screening for metastatic liver disease, for example, is usually done with CT. However, US can be of use in many situations, such as the differentiation of cystic and solid lesions in the liver. Brick and colleagues found US to be of particular value when further characterization was needed for small, indeterminate lesions identified on a CT scan.¹⁸ US is also an excellent method for following measurable abdominal disease in patients who are on treatment protocols. The spatial resolution of US is currently comparable to that of CT, the study is far less expensive (usually one-third to one-half the cost of CT), it requires no contrast agent injection, and it may be more readily available at some institutions (see Chapter 30D).

Although CT is generally preferred for evaluating metastatic liver disease, US has been applied widely as the primary screening modality for asymptomatic patients who are at risk for hepatocellular carcinoma (HCC).¹⁹ Yearly US studies are recommended in people with chronic active hepatitis and some forms of cirrhosis. Screening programs typically use US in conjunction with a tumor marker such as alpha-fetoprotein. As with other liver tumors, US lacks specificity in differentiating HCC from other kinds of solid masses. In this patient population, regenerating nodules pose a particular problem. Dual-phase spiral CT may assist with tumor characterization in patients who are at risk for HCC, but for a definitive diagnosis, biopsy may still be necessary. In patients with known HCC, US has also been used to guide needle placement for percutaneous ethanol ablation, and it can also help monitor the dispersal of the toxic agent throughout the tumor.²⁰ US remains an excellent and cost-efficient method for guiding percutaneous biopsy of any hepatic or other abdominal mass, and it is also used to guide the placement of trocars to ablate metastatic liver disease (Figure 30G.5). Radiofrequency²¹ and cryoablation²² techniques are gaining popularity. On the one hand, radiofrequency ablation has an advantage over cryotherapy, in that it may be performed percutaneously (rather than at laparotomy), and the equipment is relatively inexpensive. On the other hand, cryotherapy is more appropriate for large lesions that cannot be eliminated with current radiofrequency techniques.

Figure 30G.5

US-guided biopsy, sagittal scans. An echogenic mass was identified in posterior right lobe of the liver in a patient with a history of ovarian carcinoma. A. Arrows, demarcate liver mass adjacent to diaphragm (arrowheads). A needle guide was placed on (more...)

US is the primary imaging modality for the initial evaluation of patients with jaundice, and it can demonstrate intrahepatic ductal dilation quite accurately. Although the actual identification of an obstructing lesion may not always be possible (strictures and stones may be particularly difficult to image), pancreatic masses or adenopathy should be visible in the majority of patients and can also be biopsied under US guidance.²³ Once biliary obstruction is identified, color Doppler imaging can be used to differentiate dilated biliary radicals from adjacent portal veins. This can be of practical import when percutaneous biliary drainage is being considered, since US can then be used to guide the needle into a bile duct lumen.

Although most uses for conventional US in the liver are now well established, color Doppler imaging has opened up some new windows of opportunity. In particular, color Doppler provides a noninvasive method to evaluate the hepatic vasculature. Portal vein thrombosis or compression by external masses is readily depicted with color Doppler imaging.²⁴ The identification of arterial flow in a portal vein thrombus by color or power Doppler is virtually diagnostic of malignant thrombus.²⁵ Color Doppler imaging is also an excellent method for evaluating patients with suspected Budd-Chiari syndrome, and it is capable of differentiating venous compression by tumor from thrombosis of the hepatic veins or inferior vena cava (Figure 30G.6).²⁶ A group of patients with a particularly high potential for blockage of hepatic venous outflow are those who have undergone intensive regimens of chemotherapy and radiation prior to bone marrow transplantation (hepatic veno-occlusive disease). Unlike patients with other forms of Budd-Chiari syndrome, patients with veno-occlusive disease have obstructed flow at the level of the hepatic venules, which is likely to be the result of an inflammatory response to the chemotherapy and/or radiation. In hepatic veno-cocclusive disease, the major hepatic veins remain patent and the standard imaging techniques may yield normal results. However, Doppler imaging may show reversal of portal vein flow.²⁷ Unfortunately, while this finding is highly specific, it lacks sensitivity. In most cases, if hepatic veno-occlusive disease cannot be diagnosed on clinical grounds, transvenous biopsy may eventually be necessary.

Figure 30G.6

Color flow Doppler reveals normally directed flow in one hepatic vein branch (blue, lower left) and reversed flow in an adjacent branch (red). This finding is diagnostic of Budd-Chiari syndrome.

Although Doppler imaging can be of assistance for evaluating the hepatic vasculature, it has not provided increased specificity for characterizing hepatic masses. Color Doppler imaging can assist in determining if a mass is relatively vascular or nonvascular, but so far, it has been incapable of distinguishing with certainty between various primary cancers, metastases, and benign liver lesions, particularly hemangiomas. Newer generations of ultrasound contrast agents may provide improved capability for tumor characterization, particularly when coupled with technologic adaptations of the US equipment that will further enhance the utility of these compounds.^28,29 Recent investigations using contrast-enhanced ultrasound have shown that the technique may actually prove to be superior to helical CT in identifying hepatic tumors.³⁰

Intraoperative Ultrasonography

A recent adaptation of conventional US that has direct application to the cancer patient is its intraoperative use in patients who are undergoing hepatic resection for hepatoma or metastatic disease. In this situation, US has both diagnostic and therapeutic potential. It is now generally accepted that intraoperative US is more accurate in identifying hepatic masses than any of the routinely used noninvasive techniques, including CT and MRI.³¹ The finding of previously unrecognized liver masses during intraoperative US has serious implications. Small or deep tumors may not be obvious to the operating surgeon and could be left behind without special imaging assistance. New masses may also be found intraoperatively in a separate segment or lobe of the liver, requiring a change in surgical approach.³² In some cases, depending on the location of newly found lesions, hepatic resection may not be indicated at all, and the patient may be saved a major surgical procedure that would have conferred little or no benefit. Finally, intraoperative US can be used to guide the surgeon to other (nonhepatic) abdominal tumors when such tumors have not been recognized preoperatively.

Retroperitoneal Ultrasonography

In the retroperitoneum, the primary uses for US include assessments of kidney size, contour, and internal echo characteristics, the detection of hydronephrosis, and the characterization of cystic or solid masses. Although several authors have reported specific Doppler signal patterns in renal carcinomas,³³ this is probably of little practical significance since surgery or biopsy must still be performed on all solid renal masses with the exception of the few that can be proven to be angiomyolipomas by CT. However, color Doppler imaging can be used to identify renal vein thrombosis (with or without tumor) and the level of extension of a thrombus into the inferior vena cava. In fact, inferior vena caval and iliofemoral obstructions of any type can be assessed using color Doppler.

Although US can readily demonstrate vessels in the retroperitoneum, the presence or absence of adenopathy is usually better determined with CT. A notable exception may be testicular tumors.³⁴ However, the improved accuracy of US for identifying para-aortic adenopathy in this group of diseases may be the result of the thinner body habitus of many young patients with testicular cancer, and it is probably not inherent to the type of pathology. As a general rule, US may be an excellent alternative to CT for evaluating the retroperitoneum in thin patients.

Pelvic and Endovaginal Ultrasonography

With known pelvic neoplasms, current staging procedures rely primarily on CT or MRI for definitive imaging information. However, the preliminary evaluation of most pelvic masses continues to be done with US. US has been quite successful in separating lesions that are gynecologic from those that are not and in helping to characterize lesions of the uterus and ovaries. Endovaginal scanning, in which a miniaturized transducer is inserted by the patient directly into her vagina, is now commonly used in addition to (or in place of) the older transvesical pelvic scan. The proximity of the endovaginal transducer to the uterus and ovaries produces images that are far superior to those obtained with transabdominal scanning methods. The endovaginal technique is acceptable to most women (including postmenopausal women) and does not require a full bladder.

Endovaginal US provides exquisite images of the endometrium (Figure 30G.7A) and is used extensively in patients who are on hormonal therapy to screen for the development of malignancy. In the postmenopausal population, a double-wall thickness of 4 mm or less essentially excludes endometrial malignancy and obviates the need for further invasive procedures. In patients without vaginal bleeding who are on hormone replacement therapy, the endometrium can measure up to 8 mm before biopsy needs to be considered.³⁵ Small submucosal leiomyomas and other lesions in or adjacent to the endometrium that can be responsible for abnormal vaginal bleeding can also be identified readily on endovaginal scans. To define the endometrial lining and characterize endometrial masses further, saline hysterosonography can be used. This relatively new technique is performed with an endovaginal probe while saline is instilled into the endometrial canal. Polyps, submucosal myomas, and endometrial cancers can be differentiated with a high degree of accuracy.³⁶

Figure 30G.7

Transvaginal US. A. Longitudinal US scan through uterus of a 66-year-old woman with vaginal bleeding. Uterus (arrows) is enlarged for a postmenopausal patient, measuring 4.2 cm. Endometrium (E) is markedly thickened, a finding suggestive of endometrial (more...)

In a patient with a known or suspected adnexal mass, endovaginal US can define the lesion’s internal characteristics far better than conventional US and can provide a more definitive diagnosis in many cases (Figure 30G.7B). The improved resolution of this technique may also facilitate the differentiation of a large normal ovary from a true mass. Another potential application of endovaginal US is to screen asymptomatic women for ovarian carcinoma, since the technique is capable of demonstrating ovarian lesions before they become palpable. However, unlike mammographic imaging, endovaginal US will probably not be cost effective as a screening technique, if applied to the general population because the incidence of disease is considerably low. Selected patients who are at high risk but not symptomatic (women who have a strong family history of ovarian cancer or a personal history of breast cancer) may benefit from its application,³⁷ however.

Prostatic and Transrectal Ultrasonography

A minor adaptation of the endovaginal probe that was described above allows it to be inserted into the rectum, thereby affording excellent images of the prostate and seminal vesicles. Unfortunately, its utility as a screening procedure for prostate cancer remains in question. At this point, relatively little is known about the natural history of small asymptomatic prostatic nodules, which are quite common. The transrectal technique is also nonspecific with regard to differentiating benign from malignant nodules.³⁸ Transrectal US can be an excellent guidance method for biopsy of the prostate, however, and it is widely used to guide transrectal biopsy needles into various quadrants of the gland in patients with elevated prostate-specific antigen levels.

Another use for transrectal US is to evaluate the rectal mucosa. Not all transrectal probes are optimally designed for this purpose, however, and only those having transducers oriented at 90° to the shaft of the probe will suffice. Therefore, all institutions may not be capable of performing this examination. Typical “end-fire” probes that are used for prostate examinations or endovaginal scans are not optimal because the sound beam/transducer cannot be oriented perpendicular to the rectal mucosa. Because of the excellent near-field resolution of endorectal transducers, various layers of the normal rectal mucosa can be delineated clearly; depth of invasion by rectal tumors can be depicted readily and with considerable accuracy. The data derived bear directly on avoidance of abdominoperineal resection. Additionally, submucosal lesions and local adenopathy can be identified. Several recent publications have found transrectal US to be superior to CT and other imaging modalities, both for preoperative staging and for follow-up of rectal cancer, with accuracy of endorectal US for predicting depth of invasion in the 81 to 92% range.³⁹

Testicular Ultrasonography

High-resolution US remains the primary imaging modality for evaluating scrotal masses. Intratesticular masses, which are presumed ordinarily to be malignant, may be confidently differentiated from those arising outside the gland, and lesions rendered impalpable by other overlying abnormalities (e.g., a hydrocele or varicocele) should be easily identifiable (Figure 30G.8). In this connection, patients who present with metastatic nodes in the retroperitoneum or mediastinum, whose histology is compatible with a testicular site of origin, should undergo testicular US to identify a possible occult primary. In patients undergoing treatment for lymphoma or leukemia, US may also be used to locate residual disease in the testis that may not be palpable.

Figure 30G.8

Testicular sonogram, longitudinal section through right side of scrotum in a 20-year-old man with painless enlargement of the testis. A well-defined hypoechoic mass is seen posteriorly (arrows). Mass contained multiple cystic spaces; other sections revealed (more...)

Venous Ultrasonography

US is the primary examination for evaluating deep venous thrombosis of the legs.⁴⁰ This noninvasive technique should replace contrast venography in most cases. A particular advantage of US over contrast venography in cancer patients is its ability to differentiate true thromboses from neoplasms compressing or invading the vessels.

The examination protocol for deep venous thrombosis of the legs usually consists of a combination of several sonographic techniques, including gray-scale, duplex, and color flow imaging. Gray-scale US provides high-resolution anatomic images of the veins but must include a thorough venous compression examination. US with manual compression is necessary because fresh thrombus may be totally echo free (anechoic) and, as such, indistinguishable from a patent vessel. However, compression will clearly differentiate normal from abnormal, since vessels containing thrombus will not collapse completely when pressure is applied. Duplex sonography is used to identify secondary signs of vessel compromise, such as the decrease in normal flow variations with respiration that may be seen with iliac vein thrombosis. Finally, color Doppler technology allows real-time imaging of the blood flow itself. This technique helps demonstrate veins that may be otherwise difficult to see and may even outline nonocclusive clots.

While sonography is highly sensitive as well as specific in the diagnosis of thrombi between the groin and the popliteal fossa, iliac vein compromise may be difficult to diagnose, since this area is not routinely imaged. In oncologic patients with unilateral leg swelling and a negative US scan, it may be wise to alert the sonologist to the need to image the iliac veins completely and to look for both thrombosis and/or possible tumor compression. In symptomatic patients who cannot tolerate a technically adequate US examination, alternative imaging techniques should be considered. One should also be aware that conventional contrast venography may have difficulty in opacifying the iliac veins, and CT or MR venography are probably better choices.

Subcutaneous Ultrasonography

The fine spatial resolution of high-frequency US transducers also makes US an ideal method for evaluating nonspecific subcutaneous masses (see Chapter 30E). The differential diagnostic possibilities may be several, but many of these masses have sufficiently specific appearances to obviate the need for further work-up. Masses arising from unrecognized trauma, for example, should lead to a nonvascular mixed cystic/solid appearance on the US scan, while metastatic lesions tend to produce well-defined nodules with parenchymal echo patterns. Fatty tumors, such as lipomas, are brightly echogenic with definable borders, while normal lobular fat deposits are poorly defined and blend imperceptably with the surrounding soft tissues. High-frequency sonography may also be useful in managing patients with melanoma, since masses can be detected and characterized better, and treatment responses can be monitored.⁴¹ US can also serve to direct a biopsy needle into any superficial mass when the diagnosis remains uncertain.

Summary

Modern US is an extremely versatile tool with applications to the management of cancer in many areas of the body. The uses for conventional (B-mode or real-time) techniques are well established and are known to most clinicians. Newer adaptations of US (color Doppler, intraoperative, and endoluminal scanning, in particular) provide incremental advantages that support their inclusion in the imaging armamentarium of modern cancer medicine.

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