Extracranial growth of glioblastoma multiforme

We present a 59-year-old woman who noted an enlarging lump on her forehead 6 months after a left frontotemporal craniotomy for tumor resection and chemoradiation of her primary glioblastoma multiforme (GBM). GBM is a highly aggressive intracranial neoplasm associated with the shortest survival time of any primary central nervous system malignancy. Extracranial metastasis is rare, especially without previous surgical disruption of the dura and calvarium, which has been postulated to cause seeding of the extracranial space with tumor cells. This patient's MRI revealed tumor recurrence for which she underwent repeat resection. Histopathology confirmed GBM with unmethylated O-6-methylguanine-DNA methyltransferase and wildtype isocitrate dehydrogenase 1 status, as well as tumor invasion through the bone and subdermal space. The genetic and molecular factors that predict extracranial invasion remain unclear and require further investigation. Emerging data on circulating tumor cells in GBM patients indicate that extraaxial metastasis may be part of the disease course in some, particularly in long term survivors. Furthermore, the proximity of calvarial and scalp lesions to previous surgical sites and the time course in which they emerge after surgery suggests that iatrogenic seeding may also play a role in metastasis. With heightened awareness of the phenomenon, surgical strategies such as watertight approximation of the dura, bone flap replacement, or changing surgical instruments once the intradural component is complete may prove useful to prevent seeding. Prophylactic craniospinal irradiation may also be an appropriate tool in patients at high risk for metastasis, although this population is difficult to identify.