Keywords
laser interstitial thermal therapy - meningioma - minimally invasive - operative feasibility
- skull base tumor
Introduction
Laser-induced thermotherapy (LITT) is a minimally invasive treatment modality utilized
for targeted thermal ablation of solid tumors and abnormal tissue.[1] Unlike other minimally invasive treatment systems previously used for targeted therapy
such as radiowaves, microwaves, or ultrasonography, prior systems failed to achieve
a high degree of precision. Simultaneously, continued progress in magnetic resonance
imaging (MRI) sequence acquisition and processing created the ability to follow treatment
effect in real time. Graham et al demonstrated that it was possible to quantify with
continuous MRI acquisition the damage produced with the tissue heating with LITT.[2] After a decade of development of both techniques and the approval of United States
Food and Drug Administration for its use in humans in 2007, the use of MR-guided LITT
(MRgLITT) was confirmed as a safe therapy.[3]
[4]
This technique has already been used previously in many neurological pathologies such
as intracranial tumors,[5]
[6]
[7]
[8]
[9] epilepsy,[10] and chronic pain syndromes[11]; as well as to treat non-neurological masses such as carcinomas of the head and
neck,[12]
[13] pulmonary, hepatic, breast, abdominal, bone, and prostate tumors in a satisfactory
manner.[14]
[15]
[16]
[17]
[18]
In spite of the multitude of pathologies in which MRgLITT has been demonstrated as
an effective treatment, it has never been tested in skull base tumors. These types
of tumors due to their location and histology usually involve complex surgeries as
well as the use of radiotherapy.[19]
[20] This series of three patients depicts the feasibility and morbidity of this minimally
invasive technique and provides a justification for the judicious and not widespread
use of LITT for the treatment of skull base lesions. Institutional review board approval
was obtained prior to case study, protocol #1912831851. Individual consent was waived
as no protected health information is reported.
Case Reports
Case 1
A 77-year-old male with a left sphenoid wing meningioma previously received open craniotomy
for resection followed by 3 to 4 treatments of stereotactic radiosurgery and subsequent
endoscopic endonasal resection for recurrence. Patient presented with a constellation
of generalized weakness with a prior fall and episodic altered mental status. Physical
exam revealed left eye blindness with left ptosis and absent left eye extraocular
movements. MRI revealed a 5.3 × 3.8 × 4.6 cm left sphenoid wing meningioma with invasion
of the left cavernous sinus and encasement of the third cranial nerve and left internal
carotid artery (ICA) with narrowing. Further appreciated was vasogenic edema of the
frontal and temporal lobes resulting in partial effacement of the lateral ventricle
and 6 mm of mid-line shift ([Fig. 1]).
Fig. 1 Preoperative (A, B), intraoperative (C, D), and postoperative (E, F) imaging for patient 1.
Patient underwent minimally invasive MRgLITT with targeting of the temporal portion
of the lesion. Patient had no complications or new cranial nerve deficits. He was
discharged home on postoperative day (POD) 3.
Postop MRI completed approximately 7 weeks following surgery revealed ablation of
the meningioma along the laser fiber tract without recurrence and improved frontal
and temporal vasogenic edema. Patient had a waxing-and-waning course. He was diagnosed
with pneumonia (PNA) and developed worsened responsiveness. Family opted for hospice
on POD 60.
Case 2
A 67-year-old female diagnosed with left trigeminal neuralgia secondary to left trigeminal
schwannoma, was initially managed with left craniotomy for subtotal resection of the
tumor followed by intensity-modulated radiation therapy for the residual lesion in
the cavernous sinus. She subsequently experienced recurrent episodic facial pain and
underwent gamma knife radiosurgery followed by trigeminal nerve rhizotomy. Of note,
patient has a significant cardiac history with a cardiac pacemaker.
Patient presented with recurrent face pain consisting of both atypical facial pain
and episodic pain in the V1 distribution triggered by talking and eating. MRI revealed
schwannoma invading the left cavernous sinus with compression of Meckel's cave ([Fig. 2]).
Fig. 2 Preoperative (A, B), intraoperative (C, D), and postoperative (E, F) imaging for patient 2.
Patient underwent MRgLITT with targeting of the anteromedial aspect of the tumor.
Patient had no immediate postoperative complications. Patient reported immediate postop
resolution of V1 distribution pain with mild V2/V3 pain. She was discharged POD 7.
Patient continued to report improvement in facial pain at 2-week follow-up. At subsequent
4-week follow-up, she reported onset of atypical facial pain with left facial hypoesthesia.
She went on to receive trigeminal nerve stimulator and then cingulotomy. Patient currently
reports only mild left-sided facial pain.
Case 3
A 52-year-old female with morbid obesity (body mass index [BMI] of 72) and no prior
history of intracranial tumor presented for workup following a fall. She reported
headache (HA), intermittent dizziness, and black spots in vision. Physical exam revealed
no cranial nerve deficits. MRI showed a right petrous apex meningioma with extension
to the right cavernous sinus, encasement and stenosis of the right ICA, and extension
into the optic canal, foramen rotundum, foramen ovale, superior orbital fissure, and
right internal auditory canal ([Fig. 3]).
Fig. 3 Preoperative (A, B), intraoperative (C, D), and postoperative (E, F) imaging for patient 3.
Patient was determined a poor candidate for surgery secondary to BMI. She underwent
MRgLITT with targeting of the right lateral aspect. Patient suffered postoperative
V1 distribution numbness and neurotrophic keratitis. She was discharged on POD 2.
Patient had persistent neurotrophic keratitis following recovery and subsequently
underwent right lateral permanent tarsorrhaphy. She later reported hearing loss and
underwent external beam radiation therapy.
Operative Technique
Laser ablation was performed using the Visualase Thermal Therapy System (Medtronic
Inc, Dublin, Ireland). Trajectories for cannula placement were planned preoperatively
based on orientation and volume of the lesions. Trajectories chosen were along the
long axis of the lesions to maximize cytoreduction while avoiding sulci, eloquent
tissue, ventricles, and vasculature.
The LITT procedure used was similar to that reported by other groups.[5] Patients were brought to the operating room and placed under general anesthesia.
An MR-compatible head frame was applied to the patient and secured by three pins.
Patients were registered to stereotactic guidance using preoperative imaging. Using
stereotaxis, the cannula was placed using the preoperative plan of cannula placement.
The laser applicator was inserted into the target and secured in place. A postapplicator
intraoperative computed tomography scan was obtained to confirm placement. Sterile
scrub was broken, and the patient was transported to the MRI suite. T1 noncontrasted
pretreatment images and a test dose at markedly lower power was initially performed
to confirm the laser applicator was functional and not damaged during transport. Treatment
exposure was performed. All doses were monitored by the surgeon to confirm that thermal
ablation zone was sufficient. Following ablation, the laser applicator was removed
in the MRI suite. All patients received immediate enhanced MRI imaging and follow-up
imaging at 1 month and further intervals.
Pretreatment test doses were performed for temperature calibration before treatment
dosing at each ablation zone. In some instances, multiple pretreatment doses were
performed due to machine error. Multiple treatment ablations were utilized along the
path of the cannula. Treatment power and duration was determined to optimize area
of ablation. Three target temperature criteria were set for each treatment ablation,
two within the site of ablation and one outside the site of ablation.
Discussion
No current work discusses the specific feasibility of treating meningiomas when located
on the skull base with LITT. Tumors along the skull base demonstrate an increased
complexity and propose a risk of injury to cranial nerves and brainstem structures
during treatment. To our knowledge, this is the first publication describing the use
of minimally invasive technique of LITT for treating skull base meningiomas.
The use of LITT for the treatment of convexity meningiomas, recurrent meningiomas,
and dural-based lesions has been previously reported. Ivan et al reported on the treatment
of four dural-based lesions with convexity or paramedian location w/ tumor control
in 4 of 5 at time of last follow-up and no neurologic deficit following the procedure.[21] Rammo et al reported on the treatment of four meningiomas and showed increasing
tumor destruction at 2 weeks postop with no extent of tumor destruction being greater
than the original tumor suggesting good conformation of the destruction.[22]
In our series of three patients, our goal was to show the feasibility of thermal ablation
of skull base lesions. Cytoreduction along the laser cannula as evidenced by postoperative
imaging confirms both the accessibility of these lesions to laser fiber placement,
as well as successful ability to reach the targeted ablative temperature. Tumor ablation
had an additional effect of reduced cerebral edema as seen in case 1 ([Fig. 1]).
Tumor ablation volumes compared against total tumor volume and intention to treat
volume, determined as volume of tumor amenable to resection, showed very little cytoreduction
([Table 1]). Patients 2 and 3 had similar volumes of ablation with the same energy profile
per LITT. Patient 1 had nearly four times greater volume of ablation with less energy
profile per LITT parameters ([Table 1]). The reason for the difference in these ablation volumes is unclear but potentially
related to the internal composition of the tumor.
Table 1
Laser interstitial thermal therapy treatment parameters
|
Patient
|
Tumor volume (cm3)
|
Intention to treat tumor volume (cm3)
|
Ablation volume (cm3)
|
Ablation zone
|
Power of shot (Watts)
|
Time of shot (s)
|
|
1
|
39
|
20.2
|
5.8
|
1
|
4.5
|
56
|
|
|
11.25[a]
|
95[a]
|
|
2
|
4.5
|
69
|
|
|
4.5
|
29
|
|
|
11.25[a]
|
79[a]
|
|
2
|
12.4
|
9.4
|
1.5
|
1
|
15
|
50
|
|
|
65
|
27
|
|
|
75
|
68
|
|
|
11.25[a]
|
126[a]
|
|
2
|
4.65
|
19
|
|
|
4.65
|
46
|
|
|
11.25[a]
|
160[a]
|
|
3
|
25.6
|
12.8
|
1.5
|
1
|
15
|
50
|
|
|
65
|
27
|
|
|
75
|
68
|
|
|
11.25[a]
|
126[a]
|
|
2
|
4.65
|
19
|
|
|
4.65
|
46
|
|
|
11.25[a]
|
160[a]
|
a Treatment shot.
Cranial nerves face a significant risk to injury during thermal ablation of skull
base lesions. Unlike vascular structures which act as heat sinks and thus subvert
thermal injury, cranial nerves are susceptible to injury from increased temperature.
Two of three patients experienced cranial nerve injuries as a result of treatment.
Benefits of tumor ablation and reduced cerebral edema must be weighed against high
risk for cranial nerve injury and low ablation volumes by single laser fiber placement.
This technique may play some role in palliative treatment of skull base lesions but
indications must be weighed for each individual patient.
Conclusion
LITT for the treatment of skull base lesions is a technically feasible intervention.
While this intervention does result in cytoreduction and may reduce cerebral edema,
there is significant risk for cranial nerve injury and ablation volumes afforded by
a single laser fiber is small. Further investigation would be recommended before using
this technique outside of a palliative indication.
