Man with headache. No recent medical problems.
Which choice is most likely?
Solitary mass.Multiple masses.Evolving infarct.Encephalomalacia.Brain abscess.
MR BRAIN: Multiple heterogeneous, predominantly T1 hyper intense enhancing intra-axial lesions are noted. No abnormal leptomeningeal or dural contrast enhancement. A marked amount of vasogenic edema is noted surrounding the right frontal lobe lesion.
PET: The fontal lobe parasaggital mass is hypermetabolic on PET imaging.
CT Chest: There is a hypermetabolic left upper lobe nodule.
Melanoma represents 5% of all skin cancers but causes 65% of all skin cancer related deaths. About half of all cases at the time of presentation are invasive. It is the most common cancer in women aged 25-29. The average age at diagnosis is 55. Fair skin, intermittent blistering sunburns, and history of prior skin cancer are all risk factors for developing melanoma.
Patients usually present with a nevus that may have asymmetry, irregular borders, color variation, and is larger than 6mm. Metastatic disease has a wide variety of presentations depending on the location of the metastasis.
The tumor and prognosis is graded based on the depth of the lesion, the presence of absence of ulcerations and + lymph nodes. Positive lymph nodes is grade III and distant metastatic disease is grade IV. Grade I (<1-2mm without ulceration) had a 5 year survival of 91-95% and grade IV has a 5 year survival of 7-19%.
There is no proven survival benefit for adjuvant chemotherapy or radiotherapy. For early stage melanoma, intra-operative lymphatic mapping and sentinel lymph node biopsy are standard.
Radiologic overview of the diagnosis:
General: Melanoma metastatic disease can present anywhere. However common sites include the spine, brain, lung, liver, spleen, and bowel. A combination of both PET, CECT, and MR is appropriate for the evaluation of metastatic melanoma. CECT is more sensitive for small pulmonary metastasis and PET CT is more sensitive for skin, bone, lymph node or other unsuspected metastases. MR is most sensitive for intracranial metastasis.
CT: Brain, chest, abdomen, and pelvis may be helpful. Search patterns need to include the muscles and other subcutaneous soft tissues. Metastatic lesions typically show hyper enhancement. Metastatic disease within the pelvis is much more likely in patients with the primary disease below the waist.
MR: Brain MR with intravenous contrast is much more sensitive than CECT of the head for the evaluation of metastatic lesions. Melanin containing lesions are T1 hyper intense. They also often enhance with gadolinium contrast.
PET: Melanoma is almost always FDG avid. PET is often used for staging purposes to look for distant metastatic disease, upgrading the patient to stage IV (distant metastatic disease.) PET is very useful in finding unsuspecting metastatic lesions. PET can also be used intraoperatively with a hand held Geiger counter to find hypermetabolic nodes.