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Introduction Brain stem lesions are pathologically heterogeneous.[12] Despite improved brain-stem imaging by magnetic resonance and high-resolution X-ray computerized tomography, preoperative radiological diagnoses prove to be wrong in 10–20% of all cases.[134] It is therefore imperative to have a tissue diagnosis to take appropriate therapeutic measures.[24] Stereotactic biopsy of lesions in the brain stem has been performed since the 1960s.[156] We report here a series of 24 patients (14 males, ten females, age range: 6–17 years) who underwent CT-guided stereotactic biopsy for brain stem lesions by the suboccipital transcerebellar route in a semi-sitting position. Presented here is a detailed description of the transcerebellar approach used by the author and the significance and advantages of transcerebellar biopsy in the awake stage. Materials and Methods Presented herein is a series of 24 transcerebellar stereotaxic biopsy procedures performed on intrinsic lesions of the mesencephalon, pons, and the medulla from March 2004 to December 2007 at the Apollo Speciality Hospital, Chennai. Eleven patients had midbrain lesions, eight had pontine, and five had ponto-medullary lesions. Procedures were carried out using general endotracheal anesthesia in six patients (four males, two females, age range: 6–10 years) whereas biopsy was performed in the awake state in othe ther 18 patients (ten males, eight females, age range: 7–17 years).

lesions, eight had pontine, and five had ponto-medullary lesions. Procedures were carried out using general endotracheal anesthesia in six patients (four males, two females, age range: 6–10 years) whereas biopsy was performed in the awake state in othe ther 18 patients (ten males, eight females, age range: 7–17 years). The basic principle used was to violate only one pial plane with the biopsy probe not entering the ventral surface of the cerebellum in its path to avoid damage to vessels in that space. Inclusion Criteria Lesions located in the dorsal midbrain, midbrain-pontine junction, midpontine / diffuse pontine region, and ponto-medullary junction. Lateralized lesions with infiltration of the cerebellar peduncle. Exclusion Criteria Rostral midbrain lesions and lesion in the anterior part of the brainstem. Dorsallly exophytic lesions which underwent open surgery. The CRW stereotactic head ring fixation (under local anesthesia nerve block) was done as low as possible on the head to ensure that the target was accessible. The anteroposterior angulation can be adjusted as per tumor size and biopsy site. The base ring was fixed to a specially made wooden board fixed to a stretcher [Figure 1A]. A contrast CT was done with the localizer ring fixed to the head ring with 2 mm cuts in the area of interest [Figure 1B].

he target was accessible. The anteroposterior angulation can be adjusted as per tumor size and biopsy site. The base ring was fixed to a specially made wooden board fixed to a stretcher [Figure 1A]. A contrast CT was done with the localizer ring fixed to the head ring with 2 mm cuts in the area of interest [Figure 1B]. Figure 1 (A) special metallic frame holding board is attached to the adjustable mobile stretcher, (B) A contrast CT is done with the localizer ring fixed to head ring with 2mm cuts at the area of interest, (C),(D) The Sedan-Nashold biopsy needle with side cutting window with rotating inner tube at the edge of the window The patients were positioned in a semi-sitting position [Figure 2A]. An entry point was chosen below the level of the transverse sinus at an appropriate distance lateral to the midline to enable access to the tumor and to avoid vascular structures [Figure 2C]. The computerized tomography and magnetic resonance imaging were helpful in trajectory selection. Figure 2 Awake semi sitting position (to monitor the patient) transcerebellar biopsy with entry point below the level of transverse sinus and an appropriate distance lateral to the midline to enable access to the tumor and to avoid vascular structures

The patients were positioned in a semi-sitting position [Figure 2A]. An entry point was chosen below the level of the transverse sinus at an appropriate distance lateral to the midline to enable access to the tumor and to avoid vascular structures [Figure 2C]. The computerized tomography and magnetic resonance imaging were helpful in trajectory selection. Figure 2 Awake semi sitting position (to monitor the patient) transcerebellar biopsy with entry point below the level of transverse sinus and an appropriate distance lateral to the midline to enable access to the tumor and to avoid vascular structures Keeping the patient awake [Figure 2B] and clinically monitoring the procedure allowed us to make the necessary changes in the trajectory of the biopsy probe to minimize the morbidity. Samples were taken with CT-guided, stereotactic, small side-cutting Nashold biopsy forceps (diameter: 1 mm) [Figures 1C, 1D]. Histopathological diagnosis was based on intraoperative smear preparations and paraffin embedded sections. Postoperative CT scan was done routinely within two hours past surgery; any clinical deterioration within the first week after surgery was considered as morbidity. Patients who underwent biopsy in the awake stage were discharged on the same day unless their prebiopsy neurological condition was not good.

edded sections. Postoperative CT scan was done routinely within two hours past surgery; any clinical deterioration within the first week after surgery was considered as morbidity. Patients who underwent biopsy in the awake stage were discharged on the same day unless their prebiopsy neurological condition was not good. Results Histological diagnosis was established in 23 patients [11 diffuse astrocytomas [Figure 3], eight pilocytic astrocytomas [Figure 4], two tuberculous lesions, one epidermoid cyst [Figure 5], and one infarction]. Although there was no procedure-related mortality, morbidity was minimal and temporary in three patients. No consistent correlation could be made between radiographic characteristics and histological diagnoses. Figure 3 A case of diffuse pontine astrocytoma in 6 year male, transcerebellar biopsy done under GA in semi sitting position Figure 4 A case of low grade astrocytoma in 10 year female, transcerebellar awake biopsy done in semi sitting position Figure 5 A case of brain stem Epidermoid (mimicking low grade glioma on MRI image) in 16 year female, transcerebellar awake biopsy with aspiration of cyst done in semi sitting position

Figure 3 A case of diffuse pontine astrocytoma in 6 year male, transcerebellar biopsy done under GA in semi sitting position Figure 4 A case of low grade astrocytoma in 10 year female, transcerebellar awake biopsy done in semi sitting position Figure 5 A case of brain stem Epidermoid (mimicking low grade glioma on MRI image) in 16 year female, transcerebellar awake biopsy with aspiration of cyst done in semi sitting position Discussion Lesions of the brain stem constitute a separate group in neurosurgical paediatric pathology.[16] Their histological diagnosis is essential for specific treatment.[26] Different types of cysts can be found besides gliomas, tuberculomas, vascular malformations, radionecrotic lesions, or other masses.[37] Open surgery is most appropriate in tumors of the cervicomedullary junction, dorsal exophytic tumors protruding into the fourth ventricle, cystic tumors, enhancing tumors with clear margins that exert a space-occupying effect, and finally, benign tumors (i.e ., those with slow clinical progression).[23] The approach of the different target locations by distinct routes, transcerebral and transcerebellar, is still a matter of debate.[7–10] Moreover, pure medullary lesions are seldom biopsied, whereas diffuse brainstem lesions, typical of children's brainstem gliomas and rather frequent in most published series, depend less and less on the histopathological confirmation for treatment.[89]

anscerebral and transcerebellar, is still a matter of debate.[7–10] Moreover, pure medullary lesions are seldom biopsied, whereas diffuse brainstem lesions, typical of children's brainstem gliomas and rather frequent in most published series, depend less and less on the histopathological confirmation for treatment.[89] Our results indicate that biopsies of masses and fluid drainage of cystic lesions of the posterior fossa are safe and simple methods. Alternatively, open operative procedures to obtain tissue require a visible surface abnormality to guide the biopsy, and carry the risks of a major surgical procedure in already compromised patients.[31011] For these reasons, the authors consider a suboccipital, transcerebellar, stereotaxic biopsy to be the diagnostic procedure of choice in the assessment of brain stem mass lesions. Advantages of biopsy are high positive biopsy rates (96%; Literature: 92–100%), differentiating benign lesions which could mimic glioma-like inflammatory granulomas, pyogenic abscess, epidermoid cyst; and in cystic lesions, rapid amelioration of neurological symptoms.[10–12] Keeping the patient awake and clinically monitoring during the procedure allows us to make the necessary changes in the trajectory of the biopsy probe to minimize the morbidity. Also, the awake transcerebellar biopsy can be done as an outpatient procedure which saves time and money.

ion of neurological symptoms.[10–12] Keeping the patient awake and clinically monitoring during the procedure allows us to make the necessary changes in the trajectory of the biopsy probe to minimize the morbidity. Also, the awake transcerebellar biopsy can be done as an outpatient procedure which saves time and money. Newer technology such as multi-planar, stereotactic magnetic resonance imaging and / or reformatted computed tomography imaging for coordinate determination and trajectory selection facilitates a completely intraaxial pathway through critical neural tissue.[1511] Conclusions A stereotaxic approach to brain-stem lesions provides a high yield of positive histological diagnoses with a low incidence of morbidity. Awake CT-guided stereotactic biopsy via the suboccipital transcerebellar route in a semi-sitting position is a safe, reliable, and effective method for brainstem lesions, that can obtain adequate tissue for histological diagnosis, thus providing each patient with the best available treatment. Source of Support: Nil Conflict of Interest: None declared.