The incidence of pineal tumors varies from 1 to 4% of brain tumors to approximately 11% in pediatric population. However, only small number of cases has serological diagnostic markers [9, 10].
The fore-mentioned fact explains why the initial tumor biopsy is considered as the cornerstone in treatment strategy plan design [2].
Three different techniques are reported in obtaining pineal tumor biopsy. The first is open microsurgical approach which is feasible but associated with morbidity and mortality only in difficult tumor excision like meningioma. The second is the stereotactic biopsy which is considered as a minimally invasive approach with high efficacy and minimal incidence of complication, but it does not offer any help regarding associated obstructive hydrocephalus. And the endoscopic pineal biopsies which provide opportunity to manage hydrocephalus and obtain biopsy under direct visualization at the same time [9, 11, 12].
Different techniques were described to perform ETV and ETB at the same time. The use of a single compromised (midway) entry site that provide minimal traction on the fornix while performing ETV and minimal traction on the choroid plexus while performing ETB [13, 14].
The use of flexible endoscope was also applied to easily target ETV and biopsy site but it has low quality image and small working channel if compared to rigid endoscope [15].
Another technique to use two separate navigation designed burr-holes [16]. Morgenstern and Souweidane used the relation between massa intermedia and the tumor as a determinant to perform one or two burr-holes [17].
In this study, we used either single burr-hole or two burr-holes technique based on the preoperative MRI study. The trajectory for endoscopic third ventriculostomy was outlined in sagittal images by drawing a line from the target area in tuber cinereum passing through the anterior edge of the foramen of Monro (fornix) up to the cortical surface to show up desired burr-hole location. The trajectory for endoscopic tumor biopsy was outlined in sagittal images without navigation by drawing a line from the most proximal part of the tumor passing through the posterior edge of the foramen of Monro (fornix) up to the cortical surface to show up desired burr-hole location.
If these two planned burr holes are close, a single more anteriorly located (1.5–1.7 cm) precoronal burr hole was performed (17 patients). If these two planned burr holes are away enough, then two separate burr holes are necessary where an additional burr-hole located close to the hair line (3–5 cm from coronal suture) was dedicated for biopsy (eight patients).
We believe that these calculations would be extremely helpful in design of the trajectory to avoid any undue forniceal or third ventricular choroid plexus injury that may potentially complicate the procedure and pose patient at risk. We also believe that in asymmetric tumor growth, it is better to approach tumors inclined to the left side through right side burr-hole and vice versa. This puts the bulging part of the tumor in the viewing angle of the endoscope with wider area to work around and facilitate the process of tumor biopsy.
The CSF analysis of our cases shows positive cytology in only six cases (24%), four cases of them had germinomas. This highlights the necessary to obtain tumor biopsy in such cases. Another additional benefit of CSF examination in germinoma cases is to determine the need of localized tumor irradiation versus whole craniospinal irradiation.
A potential risk of endoscopic tumor biopsy is bleeding from the tumor bed, especially in these frequently vascular tumors. This bleeding may be initiated suddenly during the pull out of the biopsy sample. Biopsy-related hemorrhage varies from small tumor hemorrhage to severe intraventricular hemorrhage. The incidence of hemorrhage vary in different studies, but it is obviously technique-related, and most experienced surgeon report either no or minimal occurrence of hemorrhage [6, 9].
In this study, we used the Fogarty balloon catheter to perform balloon tamponade very early by passing the catheter through the irrigation channel and put it in standby position ready for inflation to control any troublesome bleeding that may initiate during the biopsy. This helps to reduce the operative time and amount of irrigation and/or coagulation required to control bleeding from the tumor bed.
Both endoscopic and stereotactic biopsies for pineal tumors are subject of sample error and needs special care in result interpretation. This may be attributed to heterogenicity of the tumor pathology, amount of tissue supplied for histopathology, and surgical technique applied. No significant difference between both stereotactic and endoscopic approaches was reported. And most studies report success more than 80% with endoscopic approach [9, 18, 19].
In this study, pathological diagnosis was obtained in 22 out of 25 cases (88%). The reason for difficult histopathological interpretation in the remaining three cases may be attributed to their vascular nature that necessitates excessive coagulation. Although initial coagulation may be helpful to decrease the risk of bleeding, it may risk the histopathological diagnosis by masking the biopsy sample, rendering it difficult to establish a diagnosis.
