Extracranial metastasis of recurrent glioblastoma to the parotid gland: a case report and review of the literature

Abstract

Background Glioblastomas are the most common and highly malignant primary brain tumors in adults with a median survival of 15 months even with appropriate treatment. Extracranial metastases are extremely rare due to the poor prognosis not allowing sufficient time to spread. We report an extremely rare case of extracranial metastasis of supra-tentorial glioblastoma involving the skin, subcutaneous and muscular layers, periauricular region and parotid gland, and review the literature. A total of 13 glioblastoma parotid gland metastases cases have been hitherto described. Main body of the abstract A 42-year-old man underwent surgery for right temporal glioblastoma and received 60 Gy/30 fractions radiotherapy together with temozolomide at 75 mg/m2. Seven months later, the tumor relapsed and the patient underwent a second surgery while chemotherapy continued. Fifteen months later, he complained of swelling in the right neck region. Fine needle aspiration and tru-cut biopsy revealed a high-grade malignant tumor infiltration within the parotid gland. Despite salvage chemotherapy and adjuvant radiotherapy, in his follow-up after 6 months neck swelling increased. The patient declined any treatment modality and continues his life 39 months after the primary diagnosis of intracranial glioblastoma. Short conclusion Due to the recurrence rate of intracranial glioblastoma and its malignant nature; close imaging follow-up is highly crucial. The increase in reported cases of its extracranial metastases is generally due to the modern diagnostic tools and prolonged survival attributed to the improvement in treatment modalities where now radical surgery with adjuvant radiotherapy and chemotherapy is standard protocol. Patients with glioblastomas presenting with swelling in the cervical region should be investigated to rule out parotid gland metastasis.

Letter to the editor regarding “unusual extraneural metastasis of glioblastoma”

“…[ 7 , 9 , 20 ] However, as described by Achi et al ., extracranial GBM metastases have been well-reported in the literature. [ 1 ] In fact, 0.2–2.7% of GBMs are accompanied by extracranial metastases,[ 3 ] and up to 20% of GBM patients have circulating tumor cells present in their bloodstream. [ 9 ] The reports describing extracranial GBM metastases in the literature are heterogeneous and reflect the various possible pathways of metastasis.…”

“…Iatrogenic tumor spread appears to be the main mechanism by which GBM spreads outside of the head. [ 3 , 21 ] The majority of cases of extracranial GBM metastases described occurred in patients who underwent previous craniotomy, as described in Achi et al .’s report;[ 1 , 13 , 25 , 26 ] 90–96% of extracranial GBM metastases occurred in patients who underwent prior surgery. [ 19 , 25 ] Surgical intervention inadvertently aids in tumor cell spread by helping tumor cells overcome the obstacles preventing their metastasis, such as the blood–brain barrier (BBB), poor fibronectin expression by tumor cells, and the dense encasement afforded by the dura.…”

“…[ 17 , 26 ] Furthermore, there have also been several reports of GBM metastases to the parotid gland, which is imbued with a rich lymphatic network during embryological development. [ 3 , 14 , 22 , 23 ] Similar to hematogenous dissemination, dural defects created during surgery facilitate tumor cell invasion into the dural lymphatics, and the majority of lymph node metastases occur after prior craniotomy. [ 2 ] Nevertheless, we believe the hypothesis that this newly described glymphatic network can independently facilitate that metastasis is valid, as cases of cervical lymph node metastasis have been described independent of surgical intervention.…”