Article Text
PDF
Abstract
Background Flat panel detector CT (FD-CT), three-dimensional image overlay and navigation software on contemporary fluoroscopic units generate less radiation dose while performing imaging of comparable quality to conventional CT. They can superimpose MR and CT datasets and can accurately guide percutaneous procedures providing live instrument visualization and the capability of re-imaging without patient transfer. These techniques, however, have been minimally used for accessing the head.
Materials and methods Using an Allura Xper FD20 unit (Philips Healthcare Andover, Massachusetts, USA), three-dimensional image overlay and FD-CT navigation were used for percutaneous n-butyl cyanoacrylate (nBCA) embolization of an intraorbital mass in a 69-year-old man.
Results Three-dimensional image overlay provides accurate anatomical relationships between the optic nerve and vascular portions of the mass. Percutaneous nBCA was technically successful without non-target embolization and with no significant bleeding encountered during operative resection.
Conclusion FD-CT navigation and three-dimensional image overlay provide accurate instrument guidance and spatial resolution comparable with current neuro-navigation systems while also providing real time instrument position and the ability to re-image without moving the patient. These are features not available with other types of neuro-navigation.
Statistics from Altmetric.com
Introduction
The field of neurointerventional surgery continues to expand, in part due to flat panel detector CT (FD-CT) equipped on most modern fluoroscopic systems. FD-CT produces images of comparable quality to conventional CT while generating lower radiation dose and, while more limited in fine contrast resolution, is of diagnostic quality in the evaluation of gross cerebral anatomy and higher attenuation elements (eg, hemorrhage or bone).1–10 FD-CT and associated navigation software have been used to safely and accurately guide percutaneous interventions within the spine, body, skull base, and head and neck.2–7 10 11 Accompanying the quality of FD-CT is the convenience and safety of being able to repeat the CT acquisition without patient transfer as well as the ability to see real time instrument position using fluoroscopic overlay.2
The use of trans-arterial or percutaneous embolization is well established for vascular malformations and hypervascular masses within the head and neck.12 Ultrasound is often used to aid in the percutaneous access of such lesions given its ability to define soft tissues, real time instrument visualization and demonstration of vessels and other vascular tissues although it can be limited by osseous anatomy or in accessing less superficial lesions.13–17 The use of CT guidance improves accuracy, especially with regard to bony structures, although this can be insufficient in soft tissue differentiation. In light of these limitations, a three-dimensional image overlay technique has been developed for FD-CT systems whereby an existing MR examination can be accurately superimposed onto a FD-CT combining the detailed bony detail of CT with the soft tissue definition of MR. The technique also provides volumetric manipulation of the overlay for procedural navigation.2
We describe the use of three-dimensional overlay in combination with FD-CT guidance for percutaneous embolization of an intraorbital mass.
Case report and technique
A 69-year-old man presented with blurry vision and a right intraorbital mass. Physical examination revealed right-sided exotropia and 20/80 vision. MR of the brain showed a multilobulated, heterogeneously enhancing vascular lesion in the retrobulbar space.
To minimize movement, the head was carefully taped to the table. Right carotid digital subtraction angiography and FD-CT (XperCT and XperGuide; Philips Healthcare, Andover, Massachusetts, USA) angiograms revealed arterial feeders from the ophthalmic artery. The FD-CT was overlaid on the previously obtained MR to better define the relationship between the mass, globe and optic nerve (figure 1). XperGuide software was used to define a target within the lesion with the entry point medial to the medial canthus. The face was prepped and a 20 gauge spinal needle was aligned using the entry point view in the AP plane. Using a progress view in the lateral plane, the needle was passed to the target along the previously defined trajectory (see video, available online). Gentle suction confirmed intravascular placement, which was found to be arterial by injection of iodinated contrast under fluoroscopy. The needle and hub were flushed with a mixture of saline and dextrose, and a 25%:75% mixture of n-butyl cyanoacrylate and ethiodol was injected under fluoroscopic observation until stasis was achieved. After a second FD-CT showed the location of the embolization material, another target was identified inferior to the embolization site, and the procedure repeated. A final FD-CT angiogram demonstrated the regions of embolization (figure 2). The procedure required 34.1 min of fluoroscopy and produced 410 Gy/cm2 dose area product.
Three-dimensional image overlay. Left: Axial post-contrast T1 image and insert demonstrating a hypervascular intra-orbital mass. Middle: Overlay and insert of a flat panel detector CT (FD-CT) (red) defining the osseous margins. Right: Overlay and insert of axial T2 image with FD-CT (red) delineating the optic nerve relative to the mass.
Post embolization. Left: Sagittal flat panel detector CT (FD-CT) image demonstrating n-butyl cyanoacrylate (nBCA) material within the intraorbital mass. Right: Overlay of post-contrast T1 on FD-CT (red) demonstrating nBCA relative to the remaining enhancing portions of the mass.
Following the procedure, no significant bleeding or hematoma was noted. The patient's vision was unchanged prior to n-butyl cyanoacrylate injection. The patient underwent subsequent craniotomy and resection of the lesion. There was no significant bleeding encountered during operative resection with a total of 50 ml of blood loss. Pathological evaluation demonstrated fibrous tissue with prominent vascularity and increased spindled cells thought to be reactive in etiology.
Discussion
The utility of trans-arterial or percutaneous embolization is well established for hypervascular lesions within the head and neck.12 Percutaneous techniques are often performed under ultrasound guidance given the ability to delineate anatomy, real time instrument visualization and demonstration of vessels and other vascular tissues.13–17 Ultrasound is, however, more operator dependant than CT guided techniques, limited by bony anatomy and often restricted to more superficial lesions. Standard CT guidance improves accuracy, particularly with regard to deeper lesions and those within or obscured by bone relative to ultrasound, although it is lacking in contrast resolution, vascular delineation and real time instrument position compared with sonography. Interventional MR is similar to CT intervention in many respects although it requires MR compatible equipment and is thus less readily available at most hospitals.
The use of three-dimensional image overlay can combine the robust soft tissue differentiation of MR with the crisp CT definition of osseous anatomy to assist interventional planning. Three-dimensional image overlay works by automated or manual fitting of a volumetric rendering of an MR or CT onto an FD-CT using a three-dimensional work station.11 Once linked, the two datasets can be manipulated and overlaid on live two-dimensional fluoroscopy. In the setting of a hypervascular lesion, as in our case, we were able to clearly identify the optic nerve as well as target the vascular portions of the mass. The three-dimensional overlay technique can also be used for guidance during endovascular procedures. MR or FD-CT angiography can be superimposed on live fluoroscopy providing a roadmap to guide endovascular procedures regardless of the re-position of the C-arm. In these situations the use of time of flight or phase contrast MR angiography techniques can potentially eliminate the need for preliminary planning digital subtraction angiography and in turn reduces the contrast volume, a significant advantage in the pediatric and renal dysfunction populations.
One of the major limitations of FD-CT navigation is the potential for patient motion. To sidestep the need for a surgical fixation device, FD-CT has the ability to correct for patient movement by quickly re-orienting the navigation overlay image on the live fluoroscopic image based on boney landmarks.2 11 If there is significant patient motion, however, FD-CT and guidance plots can be repeated without transferring the patient.
Minimally invasive surgical techniques continue to evolve, aiming to reduce procedure related morbidity and to gain access to regions considered beyond the reach of open operative methods. FD-CT navigation and three-dimensional image overlay are techniques that provide accurate instrument guidance and spatial resolution comparable with current neuro-navigation systems. These methods, however, also provide real time instrument position and the ability to re-image without moving the patient, features not available with other types of neuro-navigation. Finally, FD-CT navigation uniquely combines the ability to simultaneously perform endovascular and percutaneous intervention, adding to the therapeutic repertoire available to a neurointerventional surgeon.
Key messages
Flat panel detector CT (FD-CT) in use with contemporary fluoroscopic systems provides high resolution imaging as well as software, providing navigational guidance and MR image overlay.
Given that these tools have not been used extensively in head and neck intervention, we aimed to use them in percutaneous embolization of an intraorbital mass.
Three-dimensional MR image overlay and FD-CT were excellent in differentiating soft tissue anatomy while providing accurate guidance for needle localization.
This report demonstrates the safety, utility and technical ease of the FD-CT, three-dimensional image.
References
Supplementary materials
Web Only Data jnis.2010.002287
Files in this Data Supplement:
Footnotes
Competing interests None.
Ethics approval This study was conducted with the approval of the University of Washington institutional review board.
Patient consent Obtained.
Provenance and peer review Not commissioned; not externally peer reviewed.