William R. Stetler

Human spinal arachnoid villi revisited: immunohistological study and review of the literature.

OBJECT Few have described the relationship between arachnoid protrusions (villi) and adjacent spinal radicular veins, and the descriptions that do exist are conflicting. Some authors have even denied the presence of spinal arachnoid villi, suggesting that they play no role in cerebrospinal fluid (CSF) absorption. METHODS To further elucidate these structures, laminectomies from C-2 inferiorly to S-2 were performed in 10 fresh human adult cadavers. Following removal of the laminae, the dural nerve sleeves were identified and the spinal nerves excised 1 cm lateral and medial to the intervertebral foramina. Samples were submitted for histological and immunohistological analysis. RESULTS The authors identified arachnoid villi in all specimens. The length of these structures was approximately 50 to 170 microm. Regionally, these villi were more concentrated in the lumbar region, but they were not present at every vertebral level, with observed skip zones. Occasionally, more than one villus was identified per vertebral level. The majority of villi were intimately related to an adjacent radicular vein. There was a direct relationship between the size of the adjacent radicular vein, and the presence and number of arachnoid villi. CONCLUSIONS Findings in the present study have demonstrated that arachnoid villi exist and are morphologically associated with radicular veins. These data support the theory that CSF absorption occurs not only intracranially but also along the spinal axis. Further animal studies are necessary to prove that CSF traverses these villi and is absorbed into the spinal venous system.

Intracranial angiomatoid fibrous histiocytoma presenting as recurrent multifocal intraparenchymal hemorrhage

Angiomatoid fibrous histiocytoma (AFH) is a rare soft-tissue neoplasm that most commonly appears in the limbs, typically affecting children and young adults. The tumor has a propensity for local recurrence and recurrent hemorrhage but rarely for remote metastasis. To date, only 2 reports have documented an intracranial occurrence of the tumor (1 of which was believed to be metastatic disease). This is the second report of primary intracranial AFH. Additionally, hemorrhage from an intracranial AFH lesion has yet to be reported, and little is known about the radiographic characteristics and biological behavior of these lesions. In this report, the authors describe the case of a patient with recurrent hemorrhage due to primary multifocal intracranial AFH. Initially misdiagnosed as a cavernous malformation and then an unusual meningioma, the tumor was finally correctly identified when there was a large enough intact resection specimen to reveal the characteristic histological pattern. The diagnosis was confirmed using immunohistochemical and molecular studies.

Immunohistochemical study of the phrenic ganglion

Peripheral nerve ‘pseudoganglia’ are described in the literature with little focus on histology. The phrenic ganglia, which are located on the inferior surface of the diaphragm and are associated with the phrenic nerves, have been described by some authors as potentially sympathetic ganglia although this, to the authors’ knowledge, has not been proven. The purpose of the present study was to elucidate further the true autonomic nature of this collection of nerve cell bodies. In eight fresh adult cadavers >6 h after death, the left and right phrenic ganglia were harvested and subjected to immunochemistry. All phrenic ganglia were vasoactive intestinal polypeptide negative but tyrosine hydroxylase positive. These findings indicate that the phrenic ganglia are sympathetic ganglia with most likely a vasomotor function.

Acrel’s ganglion

No data exists in the extant literature regarding the distal swelling of the posterior interosseous nerve (Acrel’s ganglion). To further elucidate this ganglion, ten adult cadavers (20 sides) underwent dissection and histological examination of this structure. No inflammatory response was noted in these histologically normal peripheral nerve structures. No neuronal cell bodies were identified. Although the etiology of such swellings is unclear, the term “ganglia” should not be applied to these enlargements of the distal posterior interosseous nerve.