Keywords
ambient cistern - extra-axial - tentorium - vascular tumor - venous hemangioma
Introduction
Venous hemangiomas are one of the most common soft-tissue tumors,[1] representing 7% of all benign soft-tissue tumors.[2] Histologically, they are characterized as the proliferation of vascular channels whose walls contain layers of smooth muscle.[3]
[4]
[5] These tumors frequently occur in the skin and subcutaneous tissue, but rarely arise in the central nervous system (CNS).[6] We describe an extremely rare case of a venous hemangioma presenting as an extra-axial mass in the ambient cistern.
Case Report
A 32-year-old woman with no past medical history experienced lightheadedness that persisted for a week. Her neurological examination was unremarkable and her symptom resolved in a week. However, a magnetic resonance imaging (MRI) revealed an extra-axial mass in the left ambient cistern. This appeared slightly hypointense on T1-weighted images, hyperintense on T2-weighted images, and heterogeneously enhanced on postcontrast images ([Fig. 1]). Although the mass was attached to the tentorium, the lack of the apparent dural tail sign and the heterogeneous enhancement were thought to be atypical for meningiomas. The patient denied any symptoms including diplopia or abnormal facial sensation. Given its small initial size, the deep location and its incidental nature, a decision was made to observe the mass with serial imaging. The tumor remained stable for the first 3 years, but 4 years after the patient's initial presentation and MRI, it increased in size from the maximum diameter of 1.6 to 2.2 cm. Possible therapeutic effects of gamma knife radiosurgery were discussed to control the growth, but surgical resection was subsequently recommended because of the atypical imaging features of the mass.
Figure 1 Preoperative magnetic resonance imaging scans. The coronal T1-weighted (A), axial T2-weighted (B), postcontrast axial, and coronal T1-weighted (C, D) images showed an extra-axial mass with heterogeneous enhancement.
She underwent left temporal craniotomy followed by a subtemporal approach. The mass was identified as a very prominent bulge entirely contained within the tentorium, without any obvious exophytic component. This mass, covered by the medial aspect of the tentorium, was found to extend into the ambient cistern, causing significant compression on the adjacent cerebral peduncle. The center of the mass was entered by opening the superomedial tentorium. The tumor was noted to be arising from between the two layers of the anteromedial tentorial incisura. The fourth cranial nerve was displaced inferiorly by the mass. The anterior margin of the mass was just posterior to where the fourth nerve entered the cavernous sinus. The inferomedial surface of the cisternal portion of the tumor was covered by a thin capsule which was the inferior layer of the medial tentorium. No apparent adhesion to cranial nerves IV and V or the brainstem was observed. The mass had a fibrous and mildly vascular matrix, and had a gross appearance similar to a meningioma. There were no findings indicative of previous hemorrhage inside the mass. After aggressive central debulking, the mass was completely dissected off of the fourth and fifth cranial nerves, adjacent posterior cerebral and superior cerebellar arteries, and the brainstem. No apparent invasion to the posterior cavernous sinus was noted.
Her postoperative course was uneventful without any neurological deficit. Her MRI showed gross total resection ([Fig. 2]). Pathological examination revealed dense fibrous connective tissue with an accompanying proliferation of vessels marked by thickened walls ([Fig. 3A]). A spindle cell proliferation in the vessel walls did not stain with antibody to S-100 protein. Intraoperative frozen section diagnosis was schwannoma. However, a Movat stain was subsequently performed which highlighted the venous nature of the back-to-back vessels ([Fig. 3B]). These characteristics were compatible with a venous hemangioma. The patient was discharged 3 days after surgery without neurological deficits.
Figure 2 A postoperative magnetic resonance imaging scan showing gross total resection.
Figure 3 Left: A photomicrograph demonstrating dense fibrous connective tissue with a spindle cell proliferation of venous vessels marked by thickened walls. Hematoxylin and eosin stain, original magnification ×100. Right: A Movat stain showed the venous nature of the back-to-back vessels in the specimen. Original magnification ×100.
Discussion
The term “hemangioma” generally refers to benign vascular tumors that include a variety of clinically and histologically distinctive entities[7] such as soft-tissue hemangiomas. The terminology is somewhat confusing because there have been many variations and overlaps in usage in the literature in reference not only to soft-tissue hemangiomas but also to cerebral vascular malformations. Soft-tissue hemangiomas are further classified as capillary, cavernous, arteriovenous, venous, and mixed according to which abnormal vascular channels are predominant.[8]
[9] For example, a cavernous hemangioma is one of the pathological subtypes of soft-tissue hemangioma, but the term “cavernous hemangioma” overlaps with one type of cerebral vascular malformations.[10] In addition, although a venous angioma is distinct from a “venous hemangioma,” some previous reports used the terms of a “venous angioma” and a hamartomatous “venous hemangioma” and interchangeably.[4] Venous angiomas are currently called developmental venous anomalies.[11] The classic description of the venous angioma is a cluster of venous radicles that converge into a collecting vein.[12] They are intraparenchymal lesions with intervening brain tissue, depicted as a sunburst pattern on MRI or angiography. In our report, we use the term “venous hemangioma” as a hamartomatous proliferation of venous vessels with the thickened wall presenting a mass lesion.
Venous hemangiomas can arise in various parts of the body. They are frequently seen in skin, subcutaneous tissue, and skeletal muscle. Also some rare locations such as the mediastinum[13] or retroperitoneal cavity[14] have been reported. Venous hemangiomas in the CNS are exceedingly rare. Our literature search found only four cases of “venous hemangiomas” in the CNS. Fermaglich et al[15] reported a case of surgical resection of a large enhanced globular mass in the optic chiasm that caused a rapid visual deterioration and subarachnoid hemorrhage. The mass contained patches of bluish discoloration and numerous blue cysts, implying previous hemorrhage. They concluded this lesion to be a venous angioma based on the microscopic findings of the numerous irregular vascular channels without the internal elastic membrane. Moore et al[6] described a case of a 1-cm-sized venous hemangioma in the internal auditory canal that caused a persistent hearing loss since 5 years before presentation. Pathological examination revealed thick-walled blood vessels with smooth muscle and absence of elastic lamina. In the series of 426 surgical cases for tumors in the cerebellopontine angle and the internal acoustic canal, Kohan et al[16] experienced two cases of vascular tumors, one of which was a venous hemangioma. The patient complained of rapidly progressive cochleovestibular symptoms. Monin et al[4] described a case of a venous hemangioma of the left optic nerve sheath. The patient had left visual loss that was progressively worsening over a course of 5 months. The tumor was located underneath the optic nerve sheath with the appearance of a purplish and fibrinous mass. Partial resection was performed and the patient's vision improved.
Signs of hemorrhage were not observed on either radiological or intraoperative findings in our case. Because of the scarcity of cases, the bleeding rate of venous hemangiomas is unknown. However, intraoperative findings of previous reports appear to indicate the possibility of frequent intralesional hemorrhage. In addition, it should be noted that the sudden onset or relatively rapid progression of symptoms were observed in three of four previously reported cases. These clinical courses are uncharacteristic for small-sized benign tumors, which might also suggest that the intralesional bleeding could be seen in venous hemangiomas. Besides, there has been no report regarding the natural history of this rare lesion although the interval growth was noted during the follow-up (of 4 years) in our case.
From a surgical point of view, a good margin for dissection was obtained in our case, as was also described in previous reports. Similar to more common tumors in this location, such as schwannomas and meningiomas, the total resection seems to be feasible without injury to the brainstem and cranial nerves.
The information regarding the incidence, natural history, pathogenesis, and treatment options for venous hemangiomas in the CNS is currently unknown. Although the need for further accumulation of similar cases is obvious to provide the above information, for extra-axial lesions that show some atypical radiological characteristics and clinical courses, a venous hemangioma should be included in the differential diagnoses.
Finally, our differential diagnosis during the patient's observation included a schwannoma, and therefore, gamma knife radiosurgery was briefly discussed as a possible management option. This case underscores the importance of obtaining a tissue diagnosis before gamma knife radiosurgery.
