LETTER TO THE EDITOR
Long-term Spontaneous Partial Regression of a Cerebral Arteriovenous Malformation: 24-Year Follow-up
2017 Volume 66 Issue 3 Pages 51-53
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2017 Volume 66 Issue 3 Pages 51-53
Spontaneous regression of arteriovenous malformations (AVMs) is rare, with a reported prevalence of 0.8–1.3%. The chief cause of AVM regression is postulated to be intranidal thrombosis;1,2,3,4 however, the underlying mechanisms are not well understood. We herein describe a patient who showed spontaneous partial regression of an AVM over a 24-year period. The thrombosis of drainers was observed sequentially on annual magnetic resonance angiography (MRA) examinations. This gradual thrombosis may have caused spontaneous regression, although in some cases it can cause AVM rupture.
A 31-year-old man had experienced gradual loss of control of his left upper and lower extremities at the age of 7 years. Magnetic resonance imaging (MRI) at that time revealed a 47-mm-diameter right thalamus AVM situated toward the midbrain that was causing mild hydrocephalus. MRA indicated that the lesion was fed by bilateral posterior cerebral arteries and posterior inferior cerebellar arteries and drained into the right cavernous sinus and the Galenic system. The AVM was categorized as Spetzler–Martin grade IV, and the hydrocephalus caused no symptoms. Therefore, the patient underwent observation and was treated conservatively.
Nine years after diagnosis, the patient experienced progressive vision disturbance caused by papilloedema, which was diagnosed by an ophthalmologist. The patient underwent ventriculoperitoneal (VP) shunt surgery (Fig. 1A, E, I, P) and was followed up at our outpatient clinic with annual MRIs. Six years after VP shunt surgery, a T1 high-intensity region on MRI suggested venous thrombosis of the drainer into the cavernous sinus (Fig. 1B, F). This region was seen to grow on the annual MRI scans, with the drainer signal flow void disappearing on MRA 7 years after shunt surgery (Fig. 1C, G, J, Q). Drainage to the Galenic system then began to thrombose and had almost disappeared by the time of the next annual scan (Fig. 1D, H, K, R). Simultaneously, the AVM showed marked regression. The AVM on the most recent MRI was 19 mm in diameter and was categorized as Spetzler–Martin Grade III (Fig. 1L, M, N, O). The patient has mild diplopia and is observed annually with outpatient MRI.
(A) T1-weighted MRI image (T1WI) 5 years after VP shunt. The arrow indicates one of the drainer of AVM to the cavernous sinus. (B, C) T1WIs 6 and 13 years after VP shunt, respectively. The drainer into the cavernous sinus has begun to embolize. (D) T1WI 14 years after VP shunt. No drainer is evident. (E–H) Time-of-flight MR angiography (TOF) images taken at the same times as A–D, respectively. The arrow in E indicates a nidus of the AVM, and the arrow in G indicates the other drainer of the AVM. After embolization of one drainer causing spontaneous regression of the AVM, marked regression is observed between G and H. (I–K) TOF images taken at 5, 13, and 14 years after VP shunt surgery, respectively. The arrow in J indicates the drainer of AVM to Galenic system. No differences were observed when the first drainer thrombosed. Regression is observed between J and K. (L) Most recent T1WI image and (M–O) most recent TOF images. (P) The oldest MRA image obtained 5 years after VP shunt surgery. The arrow indicates the nidus of the AVM. (Q, R) MRA images 8 and 9 years after P, respectively. Spontaneous regression is observed over this time. The left side of MRI images show the right side of the patient for all images.
Spontaneous AVM regression occurs in about 1% of patients.1,2,3,4 Factors causing regression are poorly understood; however, proposed etiologies are intranidal thombosis hemodynamic changes, gliosis, atherosclerosis, and hypercoagulability.1,2,3 Hemorrhage is considered the most important factor. A small nidus, a single feeder, or a single drainer may also be factors predisposing regression.1,2,5 In our case, none of these factors (including hemorrhage) were present. Unfortunately, data from MRI scans carried out before 2005 were unavailable; however, MRI revealed gradual drainer obliteration between 2005 and 2016.
First, obliteration of a drainer to the cavernous sinus was observed, and the drainer to the Galenic system remained the only major AVM drainer. Subsequently, thrombosis of this remaining main drainer gradually occurred. We speculate that these two events led to partial AVM regression in the present case. The first thrombosis created an AVM with a single drainer; the second thrombosis decreased the size of the AVM.1 This gradual thrombosis may have caused spontaneous regression, although in some cases it can cause AVM rupture.
The cause of thrombosis in the draining veins is unclear. Spontaneous regression is thought to be the natural course of this AVM. Several contributing factors have been proposed for the spontaneous regression of AVMs. These factors include arteriosclerosis, embolus, hypercoagulable state, turbulence in vessels, and hemodynamic change caused by operations.2 It is unlikely that estrogen is a factor for thrombosis in the current case because the patient is male. The patient had no particular medical history suggesting a hypercoagulable state, but it would have been advantageous if we had examined his protein C and S levels to assess clotting function.
The VP shunt operation may have been instrumental in causing thrombosis of the draining veins. There is only one previous report on the spontaneous regression of AVM after a VP shunt operation, which suggests that subdural hematoma might have caused the disappearance of AVM.6 However, such hematoma was not observed postoperatively in the present case. If the VP shunt caused the thrombosis of the draining veins in this case, inflammation as a result of the operation may have damaged the endothelium of vessels. Alternatively, altered hemodynamics of the tortuous AVM blood vessels might have initiated the thrombosis. VP shunt surgery reduces the intracranial pressure, which is thought to increase the arteriovenous shunt volume. This increased flow in tortuous drainage veins may have caused the thrombosis.
Spontaneous AVM regression is rare; however, such events can occur, sometimes over a long period. Consequently, patients with AVM should be carefully followed up with annual MRIs.1,2,5 Moreover, when AVM patients undergo VP shunt surgery, which could cause changes in blood flow in the AVM, closer follow-up should be considered.
The authors have no personal financial or institutional interest in any of the drugs, materials, or devices described in this article.
