Introduction

Meningioangiomatosis is a rare, proliferative disorder of the blood vessels of the central nervous system characterized by a leptomeningeal plaque that can invade the surrounding cerebral cortex or spinal cord.¹ It is a benign lesion that is potentially curable with surgical resection depending on accessibility of the location.² Meningioangiomatosis has been described in humans, dogs, and cattle and can be associated with meningiomas or other tumors in dogs as well as arteriovenous malformations and tumors in humans.³ Previous reports of meningioangiomatosis in dogs describe lesions in the cerebrum, brainstem, cervical spinal cord, and thoracolumbar spinal cord and show that MRI findings are not specific for the condition.^1,3–9 Although there have been previous reports of surgical treatments of other vascular malformations in the spinal cord of dogs, this is the first report of surgical resection of suspected meningioangiomatosis in a dog.^10,11

Case Report

A 5 yr old male neutered Labrador retriever was evaluated at Veterinary Referral Hospital of Hickory for pelvic limb ataxia. The dog had an 8 wk history of a slowly progressive abnormal pelvic limb gait that did not respond to treatment with nonsteroidal anti-inflammatory medications. On examination, he was ambulatory with mild pelvic limb ataxia and a moderate right pelvic limb lameness. Radiographs of the pelvis and lumbosacral vertebral column showed moderate osteoarthritis in both hips. A few days later, he was returned for computed tomography (CT) with myelogram. His examination had changed with detection of proprioceptive deficits in both hind limbs and hyper-reflexive patellar reflexes. Neuroanatomic localization was T3–L3 spinal cord segments. No significant abnormalities were found on complete blood count or chemistry. The CT with myelogram showed an expansile mass and intramedullary filling pattern at L1, which was suggestive of an intramedullary mass (Figures 1A–C). His paresis worsened the next day, which was suspected to be due to the myelogram. He was also exhibiting urinary incontinence.

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Three days after being discharged from Veterinary Referral Hospital of Hickory, the patient was referred to Carolina Veterinary Specialists. On presentation, he was found to be ambulatory with moderate pelvic limb ataxia and paraparesis, with the left hind limb being more paretic than the right hind limb. Segmental spinal cord reflexes were normal and he was not painful on palpation of the vertebral column. Neuroanatomic localization was T3–L3 spinal cord segments.

The dog was given premedications, midazolam^a (0.1 mg/kg) and hydromorphone^b (0.1 mg/kg) IV. Anesthesia was induced using propofol^c (4 mg/kg) IV and he was maintained on isoflurane^d and oxygen. He was placed in dorsal recumbency, and MRI of the lumbar vertebral column was performed using a 1.5 Tesla magnetic resonance scanner^e. The following sequences were acquired: T2-weighted (T2W) in sagittal and transverse planes; short T1 inversion recovery (STIR) in sagittal, dorsal, and transverse planes; T1-weighted (T1W) in transverse plane; and T1W following contrast (gadopentetate dimeglumine^f 103 mg/kg given IV) in dorsal and transverse planes. There was a large, 7 mm by 9 mm, circumscribed, markedly T2W/STIR hyperintense, mild T1W hyperintense, peripheral contrast-enhancing mass in the spinal cord over the vertebral body of L1. The mass appeared to be intradural (possibly intramedullary) but was not extradural (Figures 2A–D, 3A–C). There was moderate dilation of the central canal from T12 to L1 consistent with syringohydromyelia (Figures 2A–D). Differential diagnoses for this intradural (possibly intramedullary) mass included glioma, peripheral nerve sheath tumor, meningioma, hematoma, vascular malformation, or granuloma.

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The dog recovered uneventfully from anesthesia and was hospitalized overnight. Treatments included Multiple Electrolytes Injection Type 1, USP^g, pantoprazole^h (1 mg/kg) IV q 24 hr, and prednisoneⁱ (0.5 mg/kg) orally in the morning and prednisone (0.3 mg/kg) orally in the evening (12 hr apart).

Surgery was recommended for decompression and biopsy. A similar anesthetic protocol was performed and one dose of cefazolin^j (22 mg/kg) was given IV preoperatively. A left-sided hemilaminectomy was performed from the cranial articular facet of L1 to the caudal articular facet of L1 with a pneumatic drill and rongeurs. An intradural mass was identified. A 10 mm durotomy was conducted with a number 12 surgical blade, and a firm, tan mass was evident. Gentle blunt dissection was performed using a small Lewis lens loop and Bishop-Harmon forceps. The entire mass was easily removed in one piece. Following mass removal, the surrounding spinal cord tissue appeared grossly normal. The dura was not closed. Gelfoam^k was placed over the laminectomy defect.

The dog recovered uneventfully from anesthesia. He was treated for pain and anxiety with hydromorphone (0.1 mg/kg) IV q 4 hr and trazodone^l (2.8 mg/kg) orally q 8–12 hr. The next day, he was nonambulatory with marked paraparesis, with the left pelvic limb being more paretic than the right hind limb. He required expression of his bladder in the hospital and was given diazepam^m (0.5 mg/kg) orally to aid in urethral relaxation. He was discharged on day 1 after surgery. Tramadolⁿ (3.5 mg/kg) and prednisone (initial dose 0.5 mg/kg in the morning and 0.3 mg/kg in the evening) were prescribed.

Histologically, the spinal mass consisted of an irregular section of soft tissue with frequent loose interlacing streams and bundles of reactive plump polyhedral to spindle cells (meningothelial cells) with frequent minimally infiltrative, peripheral, and occasional central admixed small caliber vessels. Along the periphery there was pleocellular inflammation and rare central minimal necrosis. Mitosis was rare. There were <1 mitotic figure per 10 high-power fields. The histopathologic findings indicated a reactive vascular proliferation of an uncertain nature but most suggestive of a rare proliferative disorder of leptomeningeal blood vessels termed meningioangiomatosis (Figures 4A–D).

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Because the patient did not live in the same city as the hospital, he was unable to be re-examined. However, follow-up was achieved by viewing recent videos of the dog walking. A board-certified neurologist and neurology resident viewed the videos and found that he was ambulatory with mild hind limb ataxia. There was no deterioration of signs within 18 mo following surgery.

Discussion

Meningioangiomatosis is a rare, benign malformation of the leptomeningeal blood vessels that results in formation of a focal plaque consisting of meningothelial or fibroblastic spindle-shaped cells on the surface of the brain or spinal cord.⁴ There is proliferation of blood vessels in the leptomeninges that can invade the neural parenchyma through the perivascular spaces.^3,12 The origin for meningioangiomatosis has been debated and current theories include that it is a hamartoma, leptomeningeal meningioma, or vascular malformation.^5,13 Immunohistochemistry has demonstrated a role of mesenchymal cells in meningioangiomatosis, but no evidence of meningothelial origin has been found.^1,4,14

In a total of 11 dogs, meningioangiomatosis has been reported solely in the cerebrum, brainstem, cervical spinal cord, and thoracolumbar spinal cord, with the brainstem being the most commonly affected.^1,4–9 Additionally, there has been one case of meningioangiomatosis associated with a fibrous meningioma in a Labrador retriever and meningioangiomatosis associated with a thalamic astrocytic hamartoma in a German shepherd dog.^3,8 Ages ranged from 4 mo to 9 yr old, with most dogs being young adults. The present case is 5 yr old, which is older than most of the reported cases. In all previously reported cases, diagnosis was made during necropsy. There have been about 130 cases of meningioangiomatosis reported in humans ages 14 mo to 60 yr old, with most patients being teenagers and young adults. It is most frequently seen in the brain, specifically within the right hemisphere.¹⁵ There are two types including neurofibromatosis type 2–associated meningioangiomatosis and sporadic meningioangiomatosis, with sporadic being more common. Neurofibromatosis type 2–associated meningioangiomatosis is not associated with clinical signs, and it is typically diagnosed on autopsy.² Sporadic meningioangiomatosis has also been detected in association with other tumors and vascular malformations including meningiomas, arteriovenous malformations, encephaloceles, oligodendroglioma, meningeal hemangiopericytomas, and orbital erosion.¹⁶

Clinical signs associated with meningioangiomatosis vary according to location. Previous reports of meningioangiomatosis in dogs describe clinical signs associated with lesions in the cerebrum, brainstem, cervical spinal cord, and thoracolumbar spinal cord. Dogs with cerebral meningioangiomatosis frequently are mentally dull with gait abnormalities and postural deficits.⁵ In humans, the most common clinical signs of cerebral meningioangiomatosis are focal seizures and headaches.¹⁴

CT and MRI findings of meningioangiomatosis are variable and not specific.^4,14 MRI findings of the present case were a T2W/STIR/T1W hyperintense, intradural mass with peripheral contrast enhancement. The only other report of an MRI of spinal cord meningioangiomatosis showed a lesion that was heterogeneous T2W hyperintense with a hypointense center, mild T1W hyperintense and strongly contrast enhancing.⁴ These lesions were likely T1W hyperintense owing to the presence of methemoglobin as a result of subacute hemorrhage or slow-flowing blood.¹⁷ Reports of canine intracranial meningioangiomatosis have shown masses that were either T1W hyperintense or T1W hypointense and T2W hyperintense with varying degrees of contrast enhancement on MRI.^1,4 In humans, CT images may show round lesions that are slightly iso- to hyperattenuating. However, there could also be areas of hypoattenuation on normal images.^13,14,16 Additionally, calcification and hypertrophy of the cortex can be detected. On MRI, masses are isointense to hypointense on T1W images and heterogeneous hyperintense on T2W/fluid-attenuated inversion recovery images. Most of the lesions in people do not contrast enhance.² Findings that support a diagnosis of meningioangiomatosis in the brain in humans include a small, solid mass in the superficial cortex that is isointense compared with gray matter on T1W images and heterogeneous on fluid-attenuated inversion recovery images. In humans, meningioangiomatosis is frequently misdiagnosed for meningiomas, gliomas, or vascular malformations.^13,14,16 The treatment of choice for suspected meningioangiomatosis in humans is surgical resection, and the prognosis is excellent.² Dogs that were ultimately diagnosed with solely meningioangiomatosis in previous reports died or were euthanized.^1,4–7,9

Histopathologic examination of the lesion in the present case was most consistent with meningioangiomatosis. In all previous reports of meningioangiomatosis in dogs, histological findings included spindle-shaped cells admixed with small vessels. Mitoses were rare or absent in sole cases of meningioangiomatosis except in one case of meningioangiomatosis in the right cerebral hemisphere.^1,4–7 Other histopathologic findings detected with meningioangiomatosis were necrosis, gliosis, Wallerian degeneration, and reactive astrocytes.^1,5,9 Immunohistochemistry can be supportive of a diagnosis of meningioangiomatosis but was not performed in the present case. In previously reported cases, spindeloid cells were consistently vimentin positive, indicating a mesenchymal and fibroblastic origin with variable S-100 protein highlighting.^1,4–7 Additionally, reactive astrocytes were positive for glial fibrillary acidic protein and myocytes of the tunica media of blood vessels highlighted positive for smooth muscle alpha-actin.^1,7 In humans, histopathology shows leptomeningeal, meningothelial, and meningovascular proliferation with occasional calcification, psammoma bodies, fibrosis, ossification, and neurofibrillary tangles.^2,14,16 Unfortunately, immunohistochemistry has no specific diagnostic significance and is relatively unhelpful for diagnosis.^2,13

Based on the patient’s young age, the histopathologic findings similar to previous reports in dogs with meningioangiomatosis, and the excellent outcome of the patient, the diagnosis was an invasive vascular proliferation most consistent with meningioangiomatosis. An alternative vascular proliferation would be vascular hamartoma. Because of the reactive proliferation of meningothelial cells, microvasculature, and fibroblasts, this warrants a consideration of a top differential diagnosis of meningioangiomatosis, whereas a vascular hamartoma would just be composed of vascular proliferation and stroma. Although a meningioma was thought to be a differential at first based on the appearance of the mass during surgery, the histomorphologic features ruled out a meningioma.

This is the first report of a surgically resected lesion most consistent with meningioangiomatosis with clinical outcome in a canine. There have been other cases of vascular malformations including a vascular structure and hamartoma that have been treated similarly in the cervical and thoracolumbar spinal cord, respectively. Both dogs were able to function normally 1 yr after surgery.^9,10 Our case, in addition to these two cases, indicates that surgical treatment for suspected meningioangiomatosis and vascular malformations may have a good outcome.

Conclusion

This report further supports that meningioangiomatosis can be difficult to diagnose on MRI and should be considered a differential diagnosis for focal intradural (extramedullary or intramedullary) spinal cord lesions. In suspected cases of meningioangiomatosis, surgical exploration and possible resection is recommended.