Keywords
stereotactic biopsy - brainstem lesions - awake craniotomy
Introduction
Brainstem lesions contribute around 15% in children and 2% in adults of total intracranial
space occupying lesions.[1] In children, majority of these lesions are brainstem gliomas while there is a wider
heterogeneity in adults.[2] In addition to glioma, the differential diagnosis of a brainstem lesion in adults
includes other tumors, vasculitis, arteriovenous malformation, hematoma, infarction,
infections, gliosis, and demyelinating disease.[3]
[4] Differentiating various lesions mandates biopsy, except in cases of vascular malformations.
In the cases of diffuse intrinsic pontine gliomas, the newer studies have shown the
importance of molecular biology-based treatments necessitating stereotactic biopsy.[5]
[6]
[7] Furthermore, tissue sampling enhances the knowledge about the origin of pediatric
and adult brainstem gliomas, its cellular composition, and architecture of cells where
we have limited knowledge in this type of tumors.[8]
[9]
[10]
Open biopsy for brainstem lesions is not recommended owing to the extensive skull
base work it requires and the damage it could cause to long fiber tracts and the nuclei.[11] The frame-based stereotactic biopsy role as the minimalistic and the less morbid
procedure to the brainstem lesions has been well established in the literature.[3]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21] The present article describes the technique of stereotactic brainstem biopsy, which
includes changes to be made in the frame fixation alignment, trajectories to be taken,
type of anesthesia, awake craniotomy, and other aspects to increase the yield of the
biopsy. The authors analyzed the results of their series of brainstem biopsies as
well.
Materials and Methods
Patients having symptomatic brainstem lesions with no definitive diagnosis based on
imaging were considered for stereotactic biospy. Demographic and clinical data abstracted
from the records include age at the time of biopsy, sex, preoperative Karnofsky performance
scale, presenting symptoms, and duration of symptoms and probable differential diagnosis
before surgery. Type of anesthesia, surgical trajectory taken, number of passes, operating
time, and complications postsurgery, and final biopsy reports were collected. Predicted
differential diagnoses were determined from the review of preoperative neuroradiology
reports and neurosurgical records. Lesion location was recorded after review of the
preoperative magnetic resonance imaging (MRI) scans and computed tomographic images.
Formal pathology reports were reviewed to establish frozen section and final pathological
diagnoses. Definitive treatment given following biopsy were noted.
Technique
Stereotactic biopsy was done using Cosman–Roberts–Wells (CRW) frame. All biopsies
in adult patients were done under local anesthesia (LA). General anesthesia (GA) was
preferred in pediatric patients. Some technical modifications were done in frame fixation
to target the brainstem. Some of the technical modifications required to accomplish
the brainstem biopsy include (1) fixation of the frame as low as possible, (2) Frame
is fixed with shift from the midline toward the side of the lesion. Besides that slight
rotation in an axial plane toward the side of the lesion is given to avoid the posterior
vertical bar coming in the line of trajectory. (3) Target coordinates to be based
on T2W MRI axial images obtained after the frame placement; (4) for pons and the medulla,
the trajectory was chosen through the cerebellum and subsequently, the cerebellar
peduncles. Trajectory is chosen in such a way to avoid the cranial nerve nuclei and
the tracts. (5) For the midbrain, the trajectory is taken through the cerebral hemisphere.
In cases of trans temporal trajectory to the midbrain, the arc ring system can be
fixed in such a way that the arc will be along the sagital axis of the skull with
rings in the anterior and posterior aspects. Such alignment ensures a perpendicular
trajectory through the temporal lobe to the midbrain ([Fig. 3F]). In such cases, the coordinates given by the software as anterior posterior (Y)
become lateral (X) and vice versa. (6) Semi-sitting position is preferred for the
biopsy. (7) The arc ring system is fixed reverse on the phantom base to have cylinder
downward to gain entry into the cerebellum below the transverse sinus. (8) The two
samples apart from the sample at the target were taken at a distance of 3-mm superficial
and deep instead of 10 mm.
The procedure starts by fixing the stereotactic frame under LA at pin site and sedation.
In children the frame fixation is done under GA. MRI T2 sequences are done as the
T2 sequences show the fiducials better to be recognized by the software. Any additional
sequences are done if it is required to see the lesion better. Planning is done on
the Radionics software by the Integra or frame link software by Medtronic. In adults,
the entire procedure is done under LA while in pediatric patients the procedure is
performed under GA. After the skin incision and burr hole or twist drill placement
was done, a small hole is made in the dura, sufficient enough to pass the biopsy needle.
A 5-mm Nashold biopsy needle is preferable instead of a 9-mm needle. In adults, sedation
was given if the passage of the biopsy needle through the spinal tract of the trigeminal
nerve caused tingling over the face. Before removing the head frame, immediate check
computed tomography (CT) was done in all cases to see the specs of air in the target
as well as to rule out hematomas.
Case Details
Five patients underwent stereotactic biopsy applying the technical modifications proposed
by the authors ([Table 1]). First two cases have been described in detail with images.
Table 1
Demographics, preoperative radiological location of lesion, type of anesthesia, biopsy
trajectory, postoperative complications, and final biopsy report of five patients
|
No.
|
Age/Sex
|
KPS score
|
Preoperative MRI
site of lesion
|
Anesthesia
|
Trajectory
|
Complications
|
Biopsy
|
|
Abbreviations: GA, general anesthesia; LA, local anesthesia; MRI, magnetic resonance
imaging.
|
|
1.
|
21
|
>70
|
Medulla
|
LA
|
Inferior cerebellar peduncle
|
Temporary LtUL paresthesia
|
Demyelination
|
|
2.
|
12
|
>70
|
Pons
|
GA
|
Middle cerebellar peduncle
|
Nil
|
Pilocytic astrocytoma
|
|
3.
|
50
|
<70
|
Peduncle and vermis
|
LA
|
Middle cerebellar peduncle
|
Nil
|
Lymphoma
|
|
4.
|
10
|
>70
|
Medulla
|
GA
|
Inferior cerebellar peduncle
|
Nil
|
Low-grade glioma
|
|
5.
|
18
|
>70
|
Inferior cerebellar peduncle
|
LA
|
Inferior cerebellar peduncle
|
Nil
|
Demyelination
|
Case 1
A 21-year-old-female patient presented with left upper limb paresthesia for 5 day.
She had been evaluated for this complaint and found to have right medulla and cervicomedullary
junction lesion. MRI T2-weighted images (T2WI) showed hyper intense lesion in lower
part of the medulla which was nonenhancing on contrast images. Radiological diagnosis
was demyelination versus glioma. Our neurology team evaluated her and referred her
to us for biopsy. As described above, we applied frame and biopsy was done in a semi-sitting
position and awake status. Transcerebellar biopsy was done through the inferior cerebellar
peduncle. Once the needle was advanced to the level of the spinal trigeminal tract
at the border of the pons and middle cerebellar peduncle, patient had a complaint
of severe facial pain, for which we had given a bolus of propofol. The biopsy confirmed
it as demyelination. Patient was discharged in stable condition without neurological
deficits on day 1 postoperatively ([Fig. 1]).
Fig. 1 (A) Image showing that bars should be fixed at the lowest point on the head frame. Image
showing semi-sitting position and head frame fixation on the patient as low as possible
and shifted toward the lesion side. (B) Cylinder touching the posterior X-axis which will hamper the lowest burr hole placement
if frame not fixed as low as possible on the head. (C) MRI T2WI showing trajectory passing through MCP. (D) Image showing the final burr hole placement and biopsy needle passing through the
cylinder. (E) Arc ring system fixed to the phantom base along the sagital axis of the skull with
rings in the anterior and posterior aspect. MRI, magnetic resonance imaging; T STB,
stereotactic biopsy; 2WI, T2-weighted images.
Case 2
A 12-year-old male child presented with complaints of headache. MRI showing left middle
cerebellar peduncle and brainstem junction hyperintensity in T2WI which was not enhanced
on contrast images with differential diagnosis of demyelination, glioma, and medulloblastoma
([Fig. 2]). According to the anterior-posterior, lateral, and vertical coordinates, the arc
ring system was fixed to the phantom base. Burr hole was made on the left side and
biopsy taken through middle cerebellar peduncle. Check CT was done immediately before
removing frame. Biopsy turned out to be a pilocytic astrocytoma in this patient ([Figs. 2]
[3]).
Fig. 2 Images show (A) T1 hypointense, (B) T2 hyperintense sagittal sections, (C) FLAIR hyperintensity with surrounding edema, (D) contrast mildly enhancing lesion in the left medulla. (E) Postoperative CT scan shows Burr hole site and air foci in the trajectory and target
size. FLAIR, fluid attenuated inversion recovery.
Fig. 3 (A) T1 hypointense, (B) T2 hyperintense, (C) FLAIR hyperintensity with surrounding edema, (D) contrast nonenhancing lesion in the left middle cerebellar peduncle and pons. (E) Postoperative scan showing air foci in the trajectory and target site. (F) FLAIR, fluid attenuated inversion recovery.
Discussion
Stereotactic brainstem biopsy is an essential method for diagnosis of most brainstem
lesions, considering the fact that operating on the brainstem involves high morbidity
and mortality. Molecular characterization of tumors like in pediatric diffuse brainstem
gliomas, individualized treatment concepts mandate STB (22-24).[22]
[23]
[24] Even in adults, diversity of brainstem lesions mandates tissue sampling. Frame-based
stereotactic biopsy is a more precise way of approaching the lesion with minimal damage
to the vital tracts and nuclei in the brainstem. The authors described the technical
modifications required for the routine frame fixation to achieve the desired trajectory.
In adults, our opinion to do an awake transcerebellar biopsy using a stereotactic
head frame in a semi-sitting position is a safe and effective technique compared to
an open transfrontal approach. In pediatric age group, we prefer entire procedure
including frame fixation under GA. The modifications we made to the standard surgical
technique for transcerebellar stereotactic biopsies have distinct advantages. An awake
procedure in adults also allows for patients to be monitored intraoperatively for
neurological deficits.
After making burr hole we made a small opening in the dura which is sufficient enough
to pass biopsy side cutter needle. By this we can reduce the risk of air embolus,
which is one of the major concerns when the patient is operated in the semi-sitting
position. Though prone or lateral positions have been described in the literature,[17]
[18]
[25] these positions increase the complexity of the operative step, as the Mayfield attachments
are in a posterior position on the CRW-based ring.
In the five cases, the authors had no complications, but the study has limitation
of small numbers. Samadani et al was reported diagnostic yield of 94% after the first
biopsy and 96% after the second biopsy.[26] Few studies have reported that transient and permanent neurological deficits were
4 and 1%, respectively, while 0.3% mortality was reported.[2]
Conclusion
Molecular biology and diversity of pathology mandate tissue sampling in brainstem
lesions. Although reported complications of stereotactic biopsy are rare, they could
be devastating to the patient’s life. Despite these inherent risks, successful brainstem
biopsies can individualize treatment options to the patient and provides prognostic
information as well. Frame-based stereotactic transcerebellar biopsy of the brainstem
is a safe and effective method. The technical modifications of frame fixation authors
proposed may increase the ease of getting the transcerebellar trajectory to the brainstem.
Awake STB of brainstem may increase the safety of the procedure.
