Lymph Node Metastases

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Lymph node metastases in patients with testicular tumors vary in size, from nodal masses that are < 2 cm in diameter to huge retroperitoneal masses. The character of nodal masses is related to histology; on CT, seminoma nodal deposits are usually of soft-tissue density whereas NSGCTs are often heterogeneous since they contain areas of necrosis and cystic degeneration (see Figures 6-1, C, and 6-6). Homogeneous low-density "cystic" lesions may be a feature of NSGCTs. Nodal masses associated with seminoma and nonseminomatous tumor may also calcify.

Staging CT scans are reviewed to identify nodal disease, lung metastases, and (in patients with advanced disease) bloodborne metastases in other sites. It is important that the radiologist interpreting the examination should know the side of the primary tumor in order to give appropriate weight to any equivocal findings. Edema and scarring in the groin are usually obvious on CT. The detection of nodal disease relies on size criteria, and over the last two decades there has been much discussion regarding the appropriate threshold for the upper limit of normal for retroperitoneal nodes. There is now, however, a general consensus that nodes > 8 mm in

Lymph Node Metastases Scan

Figure 6-6. Mediastinal nodal disease in a patient with disseminated testicular seminoma. A, There was bulky anterior mediastinal lymphadenopathy, which appeared of homogenenous soft-tissue density on computed tomography (CT) scan. B, There was contiguous spread of disease from the abdomen, with an enlarged right retrocrural node (arrow) measuring more than 6 mm.

Figure 6-6. Mediastinal nodal disease in a patient with disseminated testicular seminoma. A, There was bulky anterior mediastinal lymphadenopathy, which appeared of homogenenous soft-tissue density on computed tomography (CT) scan. B, There was contiguous spread of disease from the abdomen, with an enlarged right retrocrural node (arrow) measuring more than 6 mm.

short-axis diameter in the upper retroperitoneum should be considered enlarged whereas a 10 mm short-axis diameter is generally regarded as the upper limit of normal in the lower retroperitoneum. Nevertheless, it should be recognized that by defining such thresholds, a compromise is made between higher sensitivity and lower specificity and vice versa. This issue has been considered in two histo-logically correlated studies.1718 Lien and colleagues reviewed the abdominal CT scans of 90 patients who subsequently underwent retroperitoneal lym-phadenectomy as a staging procedure. In this study, which included all patients with abnormal CT scans, as well as patients with nodes of up to 2 cm in diameter, lymph node metastases were identified in 38 of the 90 patients. Applying various upper limits for the threshold of normal, these authors demonstrated the variation in sensitivities and specificities that result from the chosen criteria. Thus, if the upper limit of normal were taken as 15

Omental Caking

Figure 6-7. CT images showing unusual sites of metastic disease. Unusual sites of metastatic disease. A, Diffuse peritoneal infiltration with omental cake in a case of nonseminomatous germ cell tumor (NSGST). B, Bilateral adrenal gland involvement from relapsed semi-noma. C, Right psoas muscle metastasis from an NSGCT. D, Pleural disease from disseminated seminoma.

Figure 6-7. CT images showing unusual sites of metastic disease. Unusual sites of metastatic disease. A, Diffuse peritoneal infiltration with omental cake in a case of nonseminomatous germ cell tumor (NSGST). B, Bilateral adrenal gland involvement from relapsed semi-noma. C, Right psoas muscle metastasis from an NSGCT. D, Pleural disease from disseminated seminoma.

mm in diameter, the sensitivity would be only 37% but the specificity would be 98% whereas an upper limit of 10 mm would provide a sensitivity of 47% and a lower specificity of 87%. Other investigators have shown similar results.1819 The adoption of a threshold of 10 or 15 mm accepts false-negative rates of between 30 and 45%. Hilton and colleagues20 have shown that if an even lower threshold of 4 mm is used, the false-negative rate may be reduced from 63% (with a 10 mm threshold) to 7%. They concluded that nodes > 4 mm in diameter (especially those located anterior to the midline of the aorta) should be regarded as suspicious.

Although different institutions adopt different thresholds of the upper limit of normal, the most important factor is to be consistent within a managed group of patients. At the Royal Marsden Hospital, a lymph node that is > 10 mm in diameter (maximum short-axis diameter [MSAD]) is regarded as definitely enlarged whereas a node that is between 8 and 10 mm in MSAD is considered to be only suspicious. The subsequent decision pathway for such a patient then depends upon other clinical factors. For example, if the patient is at high risk, with histologic evi dence of vascular and lymphatic invasion, then chemotherapy will be given routinely and subsequent follow-up will give a good indication as to whether the suspicious node was involved or not, depending upon its behavior on follow-up. However, in patients who are at low risk, further procedures (such as fine-needle aspiration) may be performed.

It is important to recognize that enlarged nodes may be due to benign hyperplasia and inflammatory reaction as well as to metastatic disease. Therefore, a single enlarged node without other clinical evidence of metastatic spread should be viewed cautiously before a definitive diagnosis is made. All the limitations of CT outlined above are well established and are unlikely to be overcome even in this new era of multichannel CT.

Lymph node masses may be discretely enlarged with well-defined contours, and several enlarged nodes may be found in a cluster around the great vessels. In patients with advanced disease, tumor breaks through the lymph node capsule into the adjacent tissues, and many nodes may then coalesce (Figure 6-8). Because of the retroperitoneal pathway of metastatic spread, nodal masses are frequently closely related or involve adjacent vessels. Thus, the inferior vena cava is frequently displaced either posteriorly or anteriorly by an enlarging mass, and the renal veins may be compressed and attenuated. MRI is superior to CT in demonstrating the vascular anatomy, on account of its multiplanar capability and high-contrast resolution (Figure 6-9). Tumor may invade the inferior vena cava; this is readily shown on contrast-enhanced CT or MRI. Hydronephrosis is an important and common complication of advanced retroperitoneal disease.

In the retrocrural space, lymph nodes that are > 6 mm in diameter are presumed to be enlarged (see Figure 6-6, B). It is rare to see retrocrural disease without evidence of disease in the retroperi-toneum caudally. As in other sites, retrocrural nodal disease may be either of soft-tissue density or cystic.

At the time of staging, pelvic CT should be performed to exclude nodal disease, but pelvic CT is not recommended in follow-up if the staging scan is normal and the patient has none of the risk factors associated with pelvic relapse.21 Pelvic CT should be performed down to the level of the pubic symphysis.

In patients who relapse following previous courses of chemotherapy, or in patients who have undergone radical lymphadenectomy, lymph node involvement may be seen at unusual sites. It is important to carefully assess the peritoneum and mesenteric regions22

Testis Germ Cell Tumor Metastasis

Figure 6-8. Coalescent nodal disease. Computed tomographic imaging in a man with disseminated nonseminomatous germ cell tumor showed a coalescent nodal mass surrounding the abdominal aorta. The mass was displacing the inferior vena cava to the right, with a widening of the aortocaval distance. There was also a low-attenuation metastasis in the left lobe of the liver. A small incidental cyst was noted within the left kidney.

Figure 6-8. Coalescent nodal disease. Computed tomographic imaging in a man with disseminated nonseminomatous germ cell tumor showed a coalescent nodal mass surrounding the abdominal aorta. The mass was displacing the inferior vena cava to the right, with a widening of the aortocaval distance. There was also a low-attenuation metastasis in the left lobe of the liver. A small incidental cyst was noted within the left kidney.

of such patients to look for psoas nodes18 and to review the pelvis (Figure 6-10).

Lymph node involvement within the mediastinum is readily detected by using contrast-enhanced CT. The characteristics of nodal metastases in the mediastinum are similar to those in the retroperitoneum and may be of soft-tissue density or heterogeneous masses that are partly cystic and partly solid. Scanning should commence in the lower neck so that nodal masses in the neck and supraclavicular fossa can be identified.

There are many pitfalls in the diagnosis of retroperitoneal and mediastinal lymphadenopathy. These include vascular anomalies such as a retro- or circum-aortic renal vein, duplication of the inferior vena cava, left ascending lumbar communicating veins, and a left-sided inferior vena cava (Figure 6-11).23,24 Such anomalies are usually easily seen on contrast-enhanced CT scans but occasionally can cause confusion, particularly if an intravenous contrast medium has not been used. It is important to note these anomalies in all patients at the time of staging as such information is important for planning therapy, whether it be surgery or radiotherapy. Other errors relate to the misinterpretation of normal structures (such as small-bowel loops or diaphragmatic crura) and to the misinterpretation of postsurgical changes after staging lymphadenectomy (Figure 6-12).25

All of these patterns of disease are shown well on CT, and generally there is no need to undertake other investigations such as MRI or ultrasonography at the time of staging. However, if MRI is being performed to assess the liver or another questionable site of spread, then retroperitoneal nodal metastases can be identified by using MRI in a manner similar to that of CT. On MRI, enlarged lymph nodes have a relatively low signal intensity on T1-weighted sequences, intermediate to high signal intensity on T2-weighted sequences, and a high signal intensity on inversion recovery sequences (eg, short-tau inversion recovery [STIR]).

PET is not undertaken as a routine staging investigation in patients with testicular tumors. However, emerging evidence suggests that PET using FDG may identify disease not detected on staging CT. Early reports suggest that PET shows advantages with respect to sensitivity compared to CT but that specificity is similar.26,27

Lymph Node Character

Figure 6-9. Displacement of the inferior vena cava by nodal disease as shown by magnetic resonance imaging (MRI) in a patient with a testicular nonseminomatous germ cell tumor. Coronal fast imaging with steady procession (FISP) (A) and axial T2-weighted images (B) showed a large multiloculated cystic mass within the right peritoneum, displacing the inferior vena cava (arrows) anteriorly and laterally. The distortion of the vascular anatomy within the retroperitoneum was best appreciated with multiplanar MRI.

Figure 6-9. Displacement of the inferior vena cava by nodal disease as shown by magnetic resonance imaging (MRI) in a patient with a testicular nonseminomatous germ cell tumor. Coronal fast imaging with steady procession (FISP) (A) and axial T2-weighted images (B) showed a large multiloculated cystic mass within the right peritoneum, displacing the inferior vena cava (arrows) anteriorly and laterally. The distortion of the vascular anatomy within the retroperitoneum was best appreciated with multiplanar MRI.

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Responses

  • gebre
    How many metastases can there be on a ct scan?
    6 years ago

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