Complicated scalp carcinoma is defined as cancer that is not amenable to traditional surgical resection or radiation therapy. In our previous E-Newsletter we discussed some of the contributing risk factors that shape a complicated scalp carcinoma, such as tissue hypoperfusion and cancer extent. These factors contribute to radiation as well as surgical failure.
As discussed previously, radiation therapy is not the treatment of choice in many of these cases. Appropriate surgical therapy involves bone treatment – i.e. resection. The most common technique of treating calvarium involved by skin cancer is burring down of bone with a high-speed bur. The depth of resection can be as little as 1 mm or all the way to the diploic space. This results in a plume of bone dust around the surgical field. Spread of cancer cells and contamination of exposed tissue has always been a theoretical risk (although a very small one). There are no reports of this in the literature or evidence of this in the author’s experience. The bone resection can be easily accomplished under local anesthesia. Calvarium is insensate without overlying scalp and galea and without underlying dura.
The second bone treatment technique involves removing the entire outer table of the calvarium utilizing a powered saw. Initially, a bony groove is carved around the involved bone with a high-speed cutting bone bur. This creates a ledge that a powered sagittal saw can engage while staying parallel to the surface of the calvarium. The outer table of calvarium is resected and submitted for histologic evaluation. The preservation of the specimen allows the pathology lab to evaluate for cancer involvement after the specimen is decalcified.
An alternative technique utilizes 3, 4, or 5 mm osteotomes to split the outer table of the calvarium from the diploic space. The osteotomes engage the bone within the depth of the previously created bony groove and are manually advanced with a mallet. This has a unique advantage of no heat production that could seal the blood vessels of the diploic space. Compared with a powered saw, manual osteotomy of the outer table of calvarium provides additional control of the depth of the resection. Inadvertent minimal penetration of the inner table of calvarium is unwelcome, although mostly inconsequential. Osteotomy technique minimizes these risks.
A modification of the bony groove technique for the outer calvarial table resection involves the Synthes Piezoelectric system. This ultrasonic surgical system starts a precise bony cut which is then engaged with an osteotome to complete the resection. See our newest surgical video demonstrating its application.
A caveat to this procedure is the possible lack or ossification of diploic space paired with a 5mm thick calvarium. Pre-operative CT scan of the skull can help better define the area of surgery and avoid injury to the patient. With the exception of the powered sagittal saw technique, the above procedures can all be done safely under sedation anesthesia in an outpatient surgical setting, as is commonly done in the Skin Cancer and Reconstructive Surgery Center.
Another indication for calvarial resection is driven by reconstructive requirements. Soft tissue coverage of previously radiated bone is challenging when the underlying bone is dead due to osteoradionecrosis. Uncovering of the vascularized diploic space can aid the healing and offer an opportunity for grafting. However, skin grafting even over the diploic space is plagued with complications of graft failure. This can be improved with two stage grafting – initially with acellular dermal replacement graft (Alloderm or Integra Dermal Regeneration Template) and then with a thin split thickness skin graft 4 weeks later. (Koenen, et al, Dermatologic Surgery 2008; 34: 357-63.
Full thickness calvarial resection is reserved for advanced cancers eroding into the bone or full thickness osteoradionecrosis with bacterial infection. These cases are almost uniformly reconstructed with microvascular free flaps.