Case Author(s): Gabriel De Simon, M.D. and Barry A. Siegel, M.D. , 12/13/00 . Rating: #D2, #Q4
Diagnosis: Malignant melanoma with splenic metastasis.
Brief history:
Melanoma of the left foot treated by local resection ten years ago, with recurrence in the left popliteal fossa in May 1999. Evaluate for metastatic disease.
Images:
Coronal whole body image.
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Posterior whole body reprojection image.
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Coronal image of the lower extremities.
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Axial CT image of the upper abdomen.
Full history/Diagnosis is available below
Diagnosis: Malignant melanoma with splenic metastasis.
Full history:
61-year-old woman diagnosed with melanoma of the left foot ten years ago, treated by local resection. A recurrence of the melanoma in the left popliteal fossa in May 1999 was treated by local resection, radiotherapy and sentinel node dissection. A recent routine CT scan of the abdomen and pelvis revealed a suspicious low-attenuation lesion in the spleen.
Radiopharmaceutical:
15 mCi F-18 fluorodeoxyglucose.
Findings:
WHOLE BODY FDG PET:
Single focus of markedly increased radiopharmaceutical uptake in the midportion of the spleen.
Incidental longitudinal ectopia of the left kidney, situated in the pelvis.
Mild right hydroureteronephrosis.
LOWER EXTREMITY FDG PET:
Diffusely increased uptake in the soft tissues at the level of the left knee.
AXIAL CT SCAN OF THE ABDOMEN:
Low-attenuation lesion in the mid spleen.
Left pelvic kidney and mild distension of the right collecting system and ureter, with no discernible cause.
Discussion:
Malignant melanoma arises from pre-existing nevi and represents about 1% of all cancers. Only a few factors influence the dissemination of melanoma. The primary tumor site appears to important in outcome, with torso lesions having a worse prognosis than lower extremity lesions.
Immunological factors may also be involved, as suggested by occasional cases of spontaneous regression of melanoma, by long periods of freedom from time of excision of the primary lesion to the development of metastases(a period of ten years in this patient), and by improved prognosis when histological examination shows a marked lymphocytic response. A series of linked sequential steps must be completed by tumor cells if a metastasis is to develop. Although some steps in this process contain stochastic elements, metastasis as a whole favors survival and growth of a few subpopulations of cells pre-existing within the parent neoplasm. The outcome of metastasis depends on the interaction of metastatic cells with different organ environments, and growth within an organ can be selective. Splenic metastases are relatively uncommon in melanoma, with a reported incidence of 1%-5%. Metastases are more common to lung (70% at autopsy), liver(58%), adrenals(50%), lymph nodes(23% with Clarke levels 2 to 4, and 75% with level 5), bone(11-17%) and to bowel and subcutis(10%). Whole body imaging with FDG PET is of great value in the localization of multiple metastatic sites and in the exclusion of an incidental benign lesion, such as a hemangioma or splenic infarct giving the low-attenuation lesion in this patient.
Once the patient develops distant metastatic disease, variables such as age, sex, primary site, thickness and ulceration of the melanoma have no bearing on the outcome. The most significant factor associated with survival in patients who have distant metastases is whether a single site or two or more organ sites, are involved. This patient with a single splenic metastasis has a better prognosis than patients with metastases to multiple organs (median survival of 7 versus 2 months). Single metastases to the lung, skin, subcutaneous tissue or lymph nodes are associated with better survival rates than visceral metastases, the longest with a single pulmonary metastasis(11 months). Survival in this patient can be enhanced by splenectomy and single agent or combination chemotherapy. Few chemotherapeutic agents have demonstrated anti-tumor activity, with Dacarbazine remaining the most active agent for treatment of systemic melanoma(response rates of 15-25%). The distribution of the increased uptake at the level of the left knee demonstrated in this patient is inconsistent with focal metastastic disease, and is likely related to previous surgery or post radiation changes.
Followup:
Patient underwent a splenectomy, with histological confirmation of a single melanoma metastatic deposit. Currently being assessed for melanoma tumor vaccine as a form of treatment.
Major teaching point(s):
1. Value of whole body FDG PET, as a single imaging modality in demonstrating local disease versus metastatic spread, and in the determination of single or multiple metastases, critical in influencing further management decisions and in estimating patient survival.
2. Value of FDG PET in the determination of incidental benign lesions, mistaken as melanoma metastases on conventional imaging studies.
ACR Codes and Keywords:
References and General Discussion of PET Tumor Imaging Studies (Anatomic field:Vascular and Lymphatic Systems, Category:Neoplasm, Neoplastic-like condition)
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Case number: pt042
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