Metastatic Melanoma

Ayodale SA Johnson Odulate, MD - Case Coordinator
Matthew P Schenker, MD - Radiology Discussion
David W Kindelberger, MD - Pathology Discussion
Steven E Seltzer, MD - Attending Radiologist

September 22, 2003

Presentation

Imaging Findings

A series of PET scan images shows avid increased uptake in the area of the right kidney, extending into the lower pole. There are also suspicious foci of increased uptake just superior and to the midline of the right kidney, in the region of the right hilum, and in the region of the bladder.

Non-contrast, T1-weighted images through the right kidney show a heterogeneous, locular mass involving the right kidney. The increased T1 signal suggests either hemorrhage or other proteinaceous products. No normal parenchyma is visible on these images. T2-weighted images are also heterogeneous. Areas that demonstrated high T1 signal are also bright on T2, suggesting that these are cystic areas containing proteinaceous fluid. These areas could correspond to the collecting system or may be part of the mass. Areas of low T2 signal are likely solid areas.

Differential Diagnosis

Diagnosis

Discussion

The right nephrectomy specimen includes a 10.5 cm mass in the lower pole. The tumor does not have typical gross characteristics of a renal cell carcinoma. The brown-pigmented areas are particularly interesting. Low power microscopy of one of these areas shows wildly pleomorphic cells with differences in nuclear size, shape and chromaticity. Brown melanin is scattered abundantly throughout, along with extensive areas of necrosis. High power microscopy reveals abnormal mitotic figures.

Radiology Discussion:

Renal metastasis should be suspected whenever there is a known primary. Imaging features are rarely pathognomonic (on the more common screening CT images associated with renal masses). In fact, many renal masses are small and asymptomatic; the widespread use of CT and ultrasound has led to increased incidental detection. In autopsies, renal metastases outnumber renal primary tumors by 4:1. Reports in the literature suggest rates of non-lymphoma renal metastases of 1.5-1.8% of the general population.(6,8) The primary tumors that are most likely to metastasize to the kidneys include lung tumors (19.8-23.3%), breast cancers (12.3%), and gastric carcinomas (11.1-15.1%). Given the decreasing incidence of gastric carcinoma and increasing incidence of melanoma, however, it is likely that melanoma will soon replace gastric carcinoma as the third most common renal metastasis.

CT is the most sensitive modality for detecting renal metastases. It can be used to evaluate the extent of disease as well as other sites of involvement. Even so, small, solitary metastases can be indistinguishable from small primary malignancies. Metastases are usually multiple, bilateral, and iso- to hypodense (10-40 HU) on an unenhanced scan. They typically demonstrate limited enhancement after contrast (5-15 HU), except in the case of highly vascular tumors (such as melanoma).

Metastatic melanoma may exhibit either an expansile (common) or an infiltrative (uncommon) growth pattern on CT. Perinephric tumor extension is typical of melanoma, but rare in other diseases. The most frequent pattern of renal manifestation is multiple, discrete, bilateral lesions. On imaging, arterial phase enhancement is similar to renal parenchyma but hypodense on later phases.

References

Bailey JE, Roubidoux MA, Dunnick NR. Secondary renal neoplasms. Abdom Imaging 1998; 23:266-274

Bracken RB, Chica G, Johnson DE, Luna M. Secondary renal neoplasms: an autopsy study. South Med J 1979; 72:806-807.

Choyke PL, White EM, Zeman RK, Jaffe MH, Clark LR. Renal metastases: clinicopathologic and radiologic correlation. Radiology 1987; 162:359-363.

Ferrozzi F, Bova D, Campodonico F. Computed tomography of renal metastases. Semin Ultrasound CT MR 1997; 18:115-121.

Klinger ME. Secondary tumors of the genitourinary tract. J Urol 1951; 65:144-153.

Pascal RR. Renal manifestations of extrarenal neoplasms. Hum Pathol 1980; 11:7-17.

Wagle DG, Moore RH, Murphy GP. Secondary carcinomas of the kidney. J Urol 1975; 114:30-32.

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