Among 80 patients who underwent posterior interhemispheric OT approach for tumor resection, there were 63 males and 17 females and their ages ranged from 3 months to 21 years with the mean and median ages being 10.3 years and 10 years, respectively. All but 6 patients had hydrocephalus. All patients were evaluated with MR and head CT.
Primary tumor resection with this approach was performed in 75 patients. The remaining 5 patients had a previous craniotomy for tumor resection. Of these, three were approached through ITSC at outside medical center and had the procedure terminated due to intraoperative hemorrhage. One patient had midbrain tumor resection through a trans-vermis/IV ventricle approach, and another patient had an interhemispheric transcallosal tumor resection both of which had incomplete tumor resection. Three patients with midbrain benign astrocytoma which failed to chemotherapy underwent subsequent craniotomy for tumor resection.
Prior to or at the craniotomy, hydrocephalus in the 74 patients was managed with ETV in 33 patients, EVD in 26 and existing VP shunt in 15. Of the 33 ETVs, 14 were ETV alone, 9 had additional placement of ETV + EVD at the pre-craniotomy stage, 9 had a concurrent endoscopic tumor biopsy and 1 had a stereotaxic biopsy for an extra-ventricular pineal region tumor. Another patient without hydrocephalus had a placement of EVD at the time of craniotomy for brain relaxation. The remaining 5 without hydrocephalus had no CSF diversion prior to the tumor resection.
Tumor histology and location are shown in Table 1. There were 32 GCTs, 22 benign gliomas, 13 pineal parenchymal tumors, 5 ATRT, 3 papillary tumor of pineal region, 2 each of medulloblastoma and epidermoid and 1 thalamic GBM. GCTs were composed of 10 germinomas, 8 teratomas (5 mature and 3 immature) and 14 NGGCTs. Among NGGCTs, 10 patients had mixed GCT composed of teratoma with germinoma and/or yolk sac tumor components. Benign gliomas (18 juvenile pilocytic astrocytoma (JPA), 3 low grade glioma, 1 pilomyxoid astrocytoma) were located in the midbrain tegmentum in 12 patients, the tectum in 3 patients, in the thalamus in 3 patients, in the SMV in 2 patients and in the superior cerebellar vermis in 2 patients.
Parieto-occipital craniotomy was performed with posterior interhemispheric OT approach. Three patients had a section of the splenium for additional transcallosal approach. Maximum tumor reduction was intended in all, however in the case of germinomas, the resection was limited intentionally to either biopsy or partial resection once a frozen section disclosed this histology. The extent of the tumor resection was gross total resection in 55, subtotal resection in 13, partial resection in 10 and biopsy in 2.
All 18 patients with mature or immature teratomas had a gross total resection. Ten of these teratomas were as a component of mixed GCT and were removed at a second look surgery following neoadjuvant chemotherapy for NGGCT. Among them, three had tumor growth during chemotherapy due to a growing teratoma which was subsequently surgically removed (Fig. 8).
Of 12 midbrain tegmentum astrocytomas, 7 had gross total resection and 3 subtotal and 2 partial resection. Astrocytomas of the tectum were resected in 2 in a gross total fashion and one with dorsal exophytic extension was partially removed. Three thalamic astrocytomas with an exophytic extension to the posterior third ventricle had gross total resection in 3 (Fig. 9). All JPAs of the SMV and the superior vermis had a gross total resection.
Among pineal tumors, 7 of 12 pineoblastomas, one pineocytoma and one of 3 papillary tumors of pineal region had a gross total resection, and the rest were subtotal resections.
All ATRTs and JPAs of the SMV, which is often in a blind spot with the ITSC approach , had a gross total resection. Superior vermis tumors, 2 JPAs and 2 medulloblastomas), and 2 epidermoid tumors had total resection.
Postoperative complications are as follows. There was one postoperative mortality (1.25%). It happened to a 6-year-old boy with an exophytic tegmentum astrocytoma who died of a midbrain dysfunction 6 weeks following a partial tumor resection. One patient had postoperative hematoma in the tumor resected cavity following germinoma resection and needed an urgent reoperation for hematoma evacuation with subsequent uneventful recovery. Progressive subdural collection was noted in 3 infants and needed a subdural peritoneal shunt.
Two patients had postoperative hemiparesis and another two had increased cerebellar ataxia after removal of the astrocytoma from the tegmentum of the midbrain. All subsequently improved following physiotherapy. Following a resection of JPA of the tectum and tegmentum junction had hemiballismus which lasted for a year and subsequently subsided. Another patient with JPA of the tectum partially extending to the tegmentum experienced postoperative loss of sensation to pain and temperature on the contralateral side of his body and limb, which never recovered over 15 years of follow up period.
Common ocular symptoms following surgery were Parinaud signs. It occurred in 24 patients. Of these, 16 were transient and subsided in 6 months to a year. The remaining 8 patients had persistent Parinaud signs which were only detected by follow up neurological examinations. Parinaud signs occurred more common after resection of pineal GCTs or pineal parenchymal tumors.
Persistent double vison occurred in 6 patients comprising of vertical double vision in 2, horizontal double vision in 2 and exotropia in 2. One teenage boy had bilateral oculomotor nerve palsy following a total resection of papillary tumor of pineal region. Homonymous hemianopia on the contralateral side of the craniotomy occurred in 2 patients, and both were transient and subsided in 2 weeks and 6 weeks, respectively.
Adjuvant therapy and outcome
All patients with germinoma and malignant NGGCT, diagnosed by either tumor marker or biopsy, were treated with neoadjuvant chemotherapy. Prior to the RT, 7 of these patients had a second look surgery to remove any lesion left following chemotherapy. These patients were enrolled in Children’s Oncology Group (COG) germ cell protocol ACNS0122, 0232, and most recently in ACNS 1123. All patients with teratoma and epidermoid underwent tumor resection alone. One mature teratoma patient had a recurrence 4 years later when the second surgery disclosed a dermoid. None of patients with pure germinoma had recurrence for over 3 and 30 years. All three patients with immature teratoma following a total resection without adjuvant therapy, had a local recurrent tumor: The first one, a 9-year-old boy had a primitive neuroectodermal tumor at recurrence a year later. He was treated with chemotherapy and RT. The second one was 21-month-old boy developed a recurrence on follow up imaging which was resected and proven to be a mature teratoma. The third one was a 9-year-old boy at diagnosis and developed a recurrence 15 years later which showed a mixed malignant GCT with immature teratoma, germinoma and yolk sac tumor components. Three patients with malignant NGGCT died despite radio-chemotherapy 6 month, 14 months and 35 months later due to tumor recurrence.
All but one child with pineoblastoma received chemotherapy followed by RT including craniospinal axis. Of 12 patients with pineoblastoma, only 3 are alive between 3 and 8 years. The other 9 patients died of tumor progression between 7 months to 4 years. One patient with pineocytoma who did not receive adjuvant therapy remains alive for 8 years without recurrence.
All 5 infants with ATRT of the SMV, with their ages ranging from 4 months to 13 months at the time of diagnosis, received intensive chemotherapy. Of these, only one had subsequent RT. All died of tumor progression with CSF disseminations between 4 months and 27 months after diagnosis. Two patients with medulloblastoma received RT followed by chemotherapy without recurrence for 6 to 7 years.
Thirteen patients with totally resected benign astrocytoma were observed without adjuvant therapy except for one child with pilomyxoid astrocytoma who was treated with COG low grade tumor chemotherapy protocol using vincristine and carboplatin. During the follow up of 3 to 25 years without adjuvant therapy, only one patient with JPA had recurrence after total resection. Among the remaining patients with incomplete tumor resection, two patients received chemotherapy, and another was treated with laser interstitial thermal therapy for the residual tumor at the outside institution. Two received RT without chemotherapy, one for a recurrent low-grade astrocytoma 3 years after subtotal resection, and another after subtotal resection of a progressive JPA affecting bilateral thalamus and tegmentum.