Patrick, Todd A.

Object Although nontraumatic spinal arteriovenous malformations and fistulas (AVMs and AVFs) restricted to the epidural space are rare, they can lead to significant neurological morbidity. Careful diagnostic imaging is essential to their detection and the delineation of the pathological anatomy. Aggressive endovascular and open operative treatment can provide arrest and reversal of neurological deficits. Methods The authors report on 6 cases of extradural AVMs/AVFs causing progressive myelopathy. Clinical findings, diagnostic evaluation, treatment, and outcome are discussed. Special consideration is given to the anatomy of the lesions and the operative techniques used to treat them. A review of the literature concerning extradural vascular malformations is also presented. Results All 6 cases of extradural AVMs had an extradural fistulous location with intradural medullary venous drainage. These cases illustrate progressive myelopathy through cord venous congestion (hypertension) that can be caused by an extradural nidus or fistula. In 4 cases, a large epidural lake was identified on angiography. At surgery, the epidural lake was obliterated and medullary drainage interrupted. All patients had stabilization of their neurological deficits and successful obliteration of the AVM/AVF was obtained. Conclusions Extradural AVMs and AVFs are a poorly described entity with published clinical experience limited to sporadic case reports and small series. Although these lesions have a purely extradural location of arteriovenous shunting and early venous drainage, they can be responsible for acute and progressive neurological symptoms similar to those caused by their dural-based intradural counterparts. With careful imaging recognition of the pathological anatomy, surgical and endovascular techniques can be used for the treatment of extradural AVMs affording effective and durable obliteration with stabilization or reversal of neurological symptoms. Venous drainage directly correlates the pathologic mechanisms of presentation. Specific attention must be paid intraoperatively to the epidural lake common to both variants so that recurrence is avoided.

✓ Metastatic seeding or iatrogenic implantation of numerous types of primary central nervous system tumors, typically along cerebrospinal fluid pathways, is a frequently described albeit rare phenomenon and has never been reported in association with vestibular schwannoma (VS). The authors present a case of inadvertent surgical implantation of VS into the cerebellar hemisphere during resection of a recurrent VS in the cerebellopontine angle and internal auditory canal. A 42-year-old man presented with a 2.5-cm right VS that was removed without complication via a retrosigmoid approach. Routine imaging performed 5 years later revealed a 1.5-cm recurrence of the VS that was subsequently removed by reopening the retrosigmoid craniotomy. Five years later—10 years after initial presentation—follow-up imaging revealed a 1-cm recurrence of the VS and a separate 2.2-cm tumor in the inferior cerebellar parenchyma with surrounding edema. Both tumors were removed without complication by reopening the previous retrosigmoid craniotomy. Histological evaluation of these tumors revealed features typical of VS and similar to those of the tissue obtained from the two prior resections. Given the similarities among these tumors in pathological appearance and mitotic index, the presence of the intraparenchymal cerebellar schwannoma was probably due to intraoperative iatrogenic implantation.