British Journal of Radiology (2005) 78, 252-254
© 2005 British Institute of Radiology
doi: 10.1259/bjr/50653404
Selective conformal radiotherapy for arteriovenous malformation involving the spinal cord
K Kishi, MD, PhD1,
S Shirai, MD1,
T Sonomura, MD2 and
M Sato, MD1
1 Department of Radiology, Wakayama Medical University (WMU), Kimiidera 811-1, Wakayama City, 641-0012 and 2 Department of Radiology, Kishiwada Tokushukai Hospital, Japan
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Abstract
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Radiotherapy has seldom been used in the treatment of arteriovenous malformations (AVM) involving the spinal cord because of the cord's limited radiation tolerance. A 57-year-old woman with progressive myelopathy due to AVM was treated with a selective conformal radiation therapy (55.6 Gy/20 days) on the nidus region preserving the spinal cord, drainer veins and involved bones. The drainers and symptoms were minimized at the end of treatment and disappeared over 2 years. This case illustrates the usefulness of selective conformal radiation therapy.
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Introduction
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Radiotherapy has been rarely used for arteriovenous malformations (AVMs) involving the spinal cord because of the low radiation tolerance of the spinal cord [1]. Radiotherapy using a selective three-dimensional plan to focus on the nidus region while preserving the spinal cord, drainer veins, and involved bones has been used successfully in one patient.
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Case report
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A 57-year-old woman was first referred to an orthopaedic surgeon, complaining of a growing mass on her right back. A blue and flat birthmark had been asymptomatic since her neonatal period, and had been neglected for decades. After accidentally bruising her back 2 months earlier, she began suffering back pain, shoulder stiffness, and gradual swelling of a mass. On admission, the mass measured 13 cm x 20 cm. During pre-operative assessment, she developed a progressive myelopathy, with intolerable pain, abnormal sensation below the thorax, unsteadiness in the upright position, and impaired micturition. She was referred to the radiotherapy department and was dependent on a wheel chair.
A colour Doppler ultrasound study found turbulent high-velocity flow signals [2] in the mass. CT myelograpy revealed compression of the dural sac and spinal cord from the 7th cervical vertebra to 2nd thoracic vertebra (Figure 1a
). Abnormal enhancement was found in the right erector spinae muscles (Figure 1b) and mass. Numerous cystic lesions in these vertebral bodies indicated a risk of fracture. MRI revealed distended epidural veins compressing the spinal cord (Figure 2a). T2 enhancement in the spinal cord was observed from C3 to C6, suggesting the presence of congestive myelopathy [3]. The abnormally enhanced region in the erector spinae muscles was due to the nidus for the epidural veins, and also for signal change in the vertebral bones [4]. The angiogram showed a typical AVM pattern with a number of feeding arteries. Early venous filling coincided with the abnormal enhancement (Figure 1c). Embolisation, surgery and combination therapy were not possible because of the large number of feeders with possible anastomoses, and of the large size of the mass.
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Figure 1. Before radiotherapy. (a) CT image during myelograpy. Compression of dural sac and spinal cord. Porous change of vertebral body. (b) Enhanced CT image. Abnormal enhancement in the right spinal erector muscles. (c) Early venous filling. (d) Dose distribution curves in radiation planning. From inside to outside, each line indicates 100%, 90%, 70%, 50%, and 30% of the prescribed dose.
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Figure 2. During and after radiotherapy. (a) T2 weighted MRI. Distended epidural veins. Note T2 hyperintensity in the spinal cord. (b) MRI image on the 21st day. The spinal cord was not compressed. The epidural vein was shrunk. (c) MRI image 1 year later. Complete disappearance of the epidural venous. No T2 enhancement in the spinal cord.
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Three-dimensional conformal radiation therapy targeted to a volume including the nidus region was planned on CT images (Figure 1d
) using eight beams. This was equivalent to the gross tumour volume (GTV) defined in ICRU report 50. A total dose of 55.6 Gy in 20 fractions in 4 weeks was given, which was equivalent to 64 Gy in 32 fractions in 6 and a half weeks using the linear quadratic model with an alpha/beta ratio of 3 Gy. The mean dose of the planning target volume (PTV) that completely included the nidus region was 49 Gy. The mean dose for the spinal cord was 20 Gy, the maximum dose 34.9 Gy and normal tissue complication probability between the C5 and the T2 level was 0%. The estimated probability for myelopathy within 5 years (TD1/5) [5] was 1%. The dose to the distended epidural veins and affected vertebral body was no higher than the spinal cord dose.
The patient complained of a transient slight increase in her lower leg pain for a few days during the first week. The difficulty passing urine diminished in the second week. She became able to walk independently and a rehabilitation program was started. MRI on the 21st day of radiotherapy showed no compression of the spinal cord, and a shrunken epidural vein (Figure 2b). MRI 1 year later showed complete disappearance of the epidural venous distension and the spinal compression (Figure 2c). No T2 enhancement of the cord was found. CT scans showed a reduction in the lytic areas. There has been no sign of myelopathy and no recurrence of symptoms for 3 years.
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Discussion
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The radiation was selectively targeted on the nidus, to decrease the transnidal flow that was responsible for the cord compression, congestion [3], and artery steal [6].
On the other hand, doses to the spinal cord, affected vertebral bones and draining veins were intentionally reduced. The lower tolerance dose of the spinal cord has long been the major constraint in giving radiotherapy [5, 7, 8]. The dose used here is associated with a 5% risk of myelopathy or necrosis within 5 years from treatment (TD5/5) (47 Gy on 20 cm of spinal cord [5]). A compressed, or haemodynamically abnormal spinal cord [6] might have an even lower tolerance dose. Thus the radiation dose given was below tolerance. The dose to the lytic vertebral body was intentionally decreased to avoid further demineralization. The dose given to the distended drainage veins was also restricted because venous impairment could be an explanation for frequent post-radiosurgery haemorrhage (7–10%) in less selective treatment [9], and because the distended veins were not an essential target. High dose radiotherapy causes a loss of tissue elasticity.
Recent developments in radiation therapy systems have enabled planning of sophisticated dose distributions, overcoming the problems of sparing organs at risk, and focusing an effective dose on the nidus. The only previous report on treatment planning for spinal AVM was a technical report on the Cyberknife system [10]. In this case a good clinical outcome was achieved through technical progress, based on a knowledge of physiology and radiotherapy physics.
Received for publication November 12, 2003.
Revision received October 26, 2004.
Accepted for publication November 23, 2004.
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References
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Abstract
Introduction
