Metastatic Melanoma to the Scalp
When looking at lumps and bumps on the skin, the first algorithm we go through is “benign or malignant?” There are usually multiple clues. First, history. Of course, I didn’t give you the history on this one, because it would give away the answer (he was being treated for metastatic melanoma). Second, the character of the lesion. As we all know, cancers grow as fast as the body will let them, but they are all marked by a relatively high metabolic rate compared to the surrounding tissue (even the lowly basal cell carcinoma induces blood vessel formation, just so it can be fed). High metabolism demands a good blood supply, so most cancers, if they are going to be successful, will be surrounded in some way with an increased blood supply. Third, what is the context, exam-wise? We see here numerous other nodules on the scalp, which would make us think “Hmmm. Multiple vascular lesions on the scalp. Unlikely to be a primary cancer.”
So, run the algorithm. Benign versus malignant. Primary versus metastatic. And the metastases seem to like skin. Although many metastases like the skin, the ones that stick out in my head are clear cell carcinoma of the kidney and melanoma. So, since there is no pigment in the lesions, I would have guessed metastatic clear cell ca, but nevertheless a metastatic process. I would biopsy with a scoop shave, and let the pathologist sort it out with immunohistochemical studies.
Why metastasize to the scalp? Well, the scalp, much like the lungs, and the liver, sees a lot of blood go through it, and it has multiple small vessels in it. If a metastasis is floating around in the bloodstream, having arrived (usually) through the lymphatics, getting dumped into the subclavians via the thoracic duct and into the general circulation. They then float around until they get wedged into a small vessel, where, if they have enough nutrition, they set up shop. They secrete cytokines which cause local proliferation of blood vessels, which allows the metastases to grow. In some cases, the growth is explosive, and in others, it is not.
Many patients are a little reticent to have their picture taken, especially when they are faced with serious consequences of disease or with a disfiguring condition. This gentleman wanted me to take his picture, so other people would be warned about melanoma and hopefully avoid the pain he endured. He passed away roughly a week after this picture was taken, from brain and lung metastases.