A case of focal and diffuse brainstem glioma
An unusual case of a mixed focal and diffuse brainstem glioma. A lesson in unusual pathology, challenging surgery, and operative technique.
Clinical Presentation
A 4 year old girl presented with a relatively long history of progressive left-sided weakness and regression of developmental milestones. The symptoms extended over a year and may have been subtly present over the previous 18 months. Her examination revealed a moderate left hemiparesis involving face, arm and leg, deafness in the right ear and quite severe ataxia. Although she could walk holding the hand of one parent, she was unable to walk unassisted. She had no dysphagia or dysphonia. She was otherwise well with no significant past medical history. Her MRI showed and intrinsic brainstem lesion.
Figure 1: T2 sagittal MRI showing the extensive intrinsic tumour within the brainstem
A diagnosis of a diffuse brainstem glioma was made on imaging characteristics alone (without biopsy) and she was commenced on several chemotherapeutic agents. Despite treatment she progressed both clinically and radiologically. The parents were offered radiotherapy but chose to seek multiple opinions from both eminent neuro-oncological centers and complimentary alternative therapists.
After extensive dialogue with the parents, surgery was offered on the basis that part of the tumor was focal. The reasons for surgery were…
- Tissue diagnosis and genetic profiling
- Reduction in tumor size would improve the chances of tolerating radiotherapy
- Increase the chances of tapering steroids rapidly
- Cytoreduction may enhance the effect of radiotherapy (if this was required)
Figure 2: MRI images showing focal and diffuse elements of the tumour. Above, Coronal T1 showing relatively focal portion of tumour; Middle, axial T2 showing focal part of tumour superiorly; Below, axial T2 showing a diffuse-looking tumor with the buried basilar sign.
Surgery
The patient was placed supine on the operating table and cranial nerves 3 to 12 were monitored as well as MEP’s and SSEP’s. Pre-opeartive signals were relatively strong. A right-sided keyhole, sub-temporal craniectomy was made. The incision was linear and just in front of the ear. A small keyhole craniectomy was then made and the inferior temporal sulcus identified. A trans-sulcal, trans-ventricular, trans-choroidal approach was chosen to achieve the best trajectory to the more superior portion of the tumor and to give the best angle to remove the more caudal component (Figure 3). The tentorium was then sectioned once the 4th cranial nerve was identified and preserved. Tumor was readily recognised and removed in a piecemeal fashion using bipolar forceps and suction ONLY. The use of ultrasonic aspiration is strongly avoided when removing gliomas. A retrosigmoid approach was not considered given the focal part was mostly supra-tentorial. An eyebrow, sub-frontal approach would have meant sacrificing some normal peduncle to enter the tumor. The focal portion was removed without incident and after 4 hours the patient was awoken and extubated. Resection was terminated after the lower cranial nerve monitoring showed some significant changes.
Figure 3: Navigation view showing the surgical approach
Figure 4: Postoperative T1 axial MRI showing the extent of the tumour resection.
Outcome
The patient was only slightly worse after surgery. The child’s balance and hemiparesis were worse but there were no new deficits. She was weaned off steroids by day 3 and discharged to a rehabilitation facility day 7. The pathology showed an anaplastic astrocytoma (WHO grade 3) and radiotherapy was recommended. The family chose not to have radiotherapy and despite the child doing very well clinically, the tumor recurred after 9 months. At 12 months the family eventually accepted radiotherapy. Although her weakness is worse, she remains off steroids and enjoys life to the fullest at 13 months after the original surgery.
Discussion
The management of brainstem gliomas is controversial. Although most pediatric neurosurgeons now agree that focal lesions should be removed and diffuse lesions do not even require a biopsy, the differentiation of these sub-types is difficult. Indeed, some have even suggested that, given the inaccuracies of diagnosis based on imaging alone, all brainstem tumors require at least a biopsy, but this remains hotly debated. The 2 radiological criteria that I value are the T1 to T2 “ratio” and the “buried” basilar artery sign. The T1 to T2 ratio refers to the great work of Fred Epstein et al. who showed that if the outline of the tumor on the T1 scan and on the T2 scan are exactly the same, the tumor is likely to be focal and therefore resectable. The “buried” basilar artery sign refers to the relationship between the basilar artery and the underlying swollen pons. If the basilar artery is symmetrically encased within the swollen pons then it is a diffuse glioma and surgery is contra-indicated. Although there are exceptions to every rule, I have found these 2 criteria to be consistently reliable.
This patient was the first patient I have seen who had the diagnostic features both of a focal lesion and a diffuse lesion. The good outcome after surgery and the likely extension of survival that she has enjoyed is testament to the existence of mixed focal/diffuse tumors that may benefit from sub-total resection with brainstem electro-physiological monitoring. I cannot stress the importance of an integrated team approach. The favourable outcome in this case was extremely dependent on several factors. Firstly, I have specialised in the treatment of brainstem tumors for at least 2 decades and have performed over 100 cases. This degree of experience is essential before taking on difficult lesions. Secondly, I have had some very poor outcomes over the last several years and would like to underscore the simple but sometimes painfully real dictum of “..when you play with fire, expect to be burnt”. Brainstem surgery is high risk. Finally, some of those poor outcomes may have been avoided with cranial nerve and long tract monitoring. Good anaesthesiology, a skilled assistant, experienced electrophysiological monitoring and alert and skilled nursing staff all contributed to this positive outcome.
For further reading
Pediatric Neurosurgery 1996;24(1):24-34.”Practical decisions in the treatment of pediatric brain stem tumors.” Epstein F, Constantini S.
This case was kindly supplied by the Charlie Teo, Conjoint Assoc. Professor, University of South Wales, Asutralia; Director, Centre for Minimally Invasive Neurosurgery
