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|LETTER TO EDITOR
|Year : 2016 | Volume
| Issue : 4 | Page : 823-825
Giant arteriovenous malformation in the conus medullaris mimicking a tumor
Lu Jia1, Hongming Ji1, Shaohua Ren1, Lirong Li1, Guoping Li2, Xuan Zhang1, Xinming Ding1
1 Department of Neurosurgery, Shanxi Provincial People's Hospital, Taiyuan, China
2 Department of Neurosurgery, West China Hospital of Sichuan University, Chengdu, China
|Date of Web Publication||5-Jul-2016|
Department of Neurosurgery, Shanxi Provincial People's Hospital, Taiyuan
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Jia L, Ji H, Ren S, Li L, Li G, Zhang X, Ding X. Giant arteriovenous malformation in the conus medullaris mimicking a tumor. Neurol India 2016;64:823-5
Spinal cord vascular malformations (SCVMs) account for 2.0–11.5% of the spinal cord lesions, with a male:female ratio of 3:1. They have a progressive natural history and a poor prognosis, if left untreated. As a special subgroup of SCVM, conus medullaris arteriovenous malformations are rare. Because of the lesional angioarchitecture and location, the characteristics of conus medullaris arteriovenous malformations differ from other subgroups of SCVM. Moreover, features vary among different types of vascular malformations. Differences in presentations and radiological appearances alter the methods of treatment.
We report one case of a giant conus medullaris arteriovenous malformation. The presentation was in the form of multiple mass lesions on magnetic resonance imaging (MRI) resembling a dermoid cyst. A timely diagnosis and a precise understanding of the angioarchitecture of these lesions helps in deciding the therapeutic corridors and in determining the treatment strategies.
A 31-year-old woman was admitted to our neurosurgical ward because of a paroxysmal lumbosacral pain lasting for 2 weeks. Two weeks prior to her admission, she developed right foot tremulousness after fatigue. The tremulousness stopped on its own and did not attract the patient's attention. However, 1 week before admission, the patient's again developed lumbosacral pain with radiation across the lower extremity. She was initially treated conservatively for “lumbar disc herniation” in another hospital, with only poor clinical recovery; following this, she was transferred to our center for further treatment.
On admission, the neurological examination revealed decreased muscle strength in both lower extremities. Strength was about grade III reaching upto the L1 level. Pain on percussion were observed on both sides of the L1–L5 spinous process with a positive straight leg raising test. No other neurological deficits were observed. The patient's blood pressure, coagulation results and platelet count were within normal limits.
The spinal MRI revealed multiple mass lesions at the L1–L5 levels. Intraspinal subdural multiple nodules of varying sizes were seen, with their diameters ranging from 2 to 13 mm, with slight hyperintensity on the T1-weighted MRI, and mixed signal intensity on the T2-weighted MRI [Figure 1]a and b. The primary radiological diagnosis was a spinal dermoid cyst. The alternative differential diagnosis was a neurofibroma.
|Figure 1: Spinal magnetic resonance imaging (MRI) showed the intraspinal subdural multiple nodules of varying sizes at the upper edge of the vertebral plane of L1– L5, with their diameter ranging from 2 to 13 mm, and having a slightly high signal intensity on T1-weighted image (a) and a mixed signal intensity on T2-weighted image (b). (c and d) Follow-up MRI performed 8 years later showed the entire lesions had disappeared|
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A surgical plan was made under the assumption that these lesions were tumors. During the operation, after opening the dura, an 18 cm malformed vessel was seen located dorsal to the cauda equina nerve roots. The vessel had a diameter of approximately 7 mm, was dark red, tortuous, and spiral, and was fully freed upto the L5 level where it had pierced through the dura from the extradural space. The vessel was resected after the complete ligation of the upper and lower ends [Figure 2]a, [Figure 2]b, [Figure 2]c, [Figure 2]d. Pathology revealed that the vascular lesions to be thrombosed and organised.
|Figure 2: Photographs at surgery (a-d): a length of approximately 18 cm of the malformed vessel at the dorsum of cauda equina nerve was seen after the dura had been incised; the vessel had a diameter of approximately 7 mm and was dark red, tortuous and spiral|
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The postoperative period was uneventful. The patient's symptoms were gradually relieved and the lady was discharged without any neurological deficits 1 week later. The follow-up MRI performed 8 years later showed that the entire lesion had disappeared [Figure 1]c and d.
In 1888, Gaupp  provided the earliest description of a spinal arteriovenous malformation. In 1916, Elsberg  described the successful surgical treatment of a spinal epidural AVM. Recently Kim et al., proposed a modified classification system for spinal arteriovenous lesions based on specific anatomical and pathophysiological factors. A new category, conus medullaris arteriovenous malformations, is described as a distinct entity in this report. They are usually composed of a cluster of abnormal blood vessels, coarse feeding artery, and arterial expansion of the draining vein. The normal high-resistance capillary system was missing in their case. The pathophysiology of neurological decline includes venous hypertension, ischemia, and mass effect from the hugely dilated venous structures. Similar to our case, the weakness and tremulousness of the lower limb were observed in the early course and perhaps originated from the vascular steal phenomenon; the lumbosacral pain occurring later was caused by nerve root compression resulting from the high pressure of the draining veins, as well as vessel expansion, and its tortuousness. Chronic progressive lower limb weakness is a typical symptom of SCVM. Malformed vessels may violate the epidural, subdural, and intramedullary parts of spine. These vessels may mainly be located in the thoracolumbar spine, followed by the thoracic and cervical spine and the conus.
In general, SCVMs characteristically have a low signal intensity on T1-weighted MRIs and a high intensity on T2-weighted MRIs, presenting as a thickened and tortuous shadow of the conus blood vessels. Moreover, the phenomenon of flow void signals may be seen on T1 and T2-weighted images. The lesion may enhance intensely on contrast-enhanced CT and MRI. These characteristics, however, are nonspecific and conus AVMs with atypical images are not rare. As their clinical and imaging presentations closely resemble those of neoplasms, demyelinating diseases or infections,  a correct preoperative diagnosis of these lesions is difficult to establish. In our case, the misdiagnosis occurred because the characteristic signal void was not evident and the lesion radiologically mimicked a tumor. The digital subtraction angiography is helpful for diagnosing an AVM; however, occasionally, the angiographic results may be negative because the lesion may be too small to be detectable, or because hemorrhage or thrombosis of the involved vessels may obliterate them.
Surgical, endovascular, and combined methods must be selectively chosen for their treatment. In order to yield good outcomes, individualized treatment should be offered based on lesional angioarchitecture and the patient's clinical status. If treated sufficiently early, the condition may easily be reversed in some cases. Conus AVMs are usually easily accessible from a posterior approach. Elimination of the mass effect on the descending nerve roots of the cauda equina may be associated with a striking improvement. The course of the feeding arteries and the draining veins should be carefully noted. The fact that sometimes the feeding arteries also supply the normal spinal cord tissue and the draining veins may have a normal structure and drainage should also be taken into account before treatment, regardless of which treatment method has been utilized. Often, the lesions in this location cannot be completely removed or blocked, otherwise the patient's condition will deteriorate.
Although a giant conus medullaris arteriovenous malformation occurs rarely, it may cause devastating neurological consequences if not diagnosed and treated in a timely manner. It should be considered in the diagnosis of lesions occupying the conus medullaris.
Financial support and sponsorship
This work supported by Science and Technology Bureau, Shanxi Province, China (No. 2014021038-6).
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]