TUMORS OF THE FORAMEN MAGNUM

Since what seems to be the first reported case of foramen magnum (F.M. ) tumor by Hallopeau in 1874, literature on tumoral pathology of this region is rather scarce ; beside reports of single cases or short seri es, there are very few large series and most of them are not recent (M eyer et coll., Yasuoka et coll., Guidetti and Spallone). The present r eport includes 230 cases of extramedullary tumors collected from 21 fr ench departments over the last ten years (series of the French Speakin g Society of Neurosurgery = S.N.C.L.F. series). Delimitation of what i s called the F.M. region is rarely given in the literature. In this re port, the inferior limit is put at the C2 level and the superior one a t the ponto-medullary junction and the lower third of the clivus. To b elong to the F.M. region, tumor must have its main part or its inserti on within these limits even if it extends beyond them. On the contrary , if the gross development is out of these limits but with some extens ion into the F.M. region, the case is rejected. A chapter of this repo rt deals with the anatomy of the F.M. with emphasis on the points usef ul for the management of the tumors. Some details are given on the dim ensions of the different parts of the F.M. as given by anatomical stud ies and also by measurements on C.T. scanner and M.R.I. including duri ng flexion and extension of the head. The S.N.C.L.F. series is then an alyzed as a whole. It includes 106 meningiomas (M), 49 neurinomas (N), 28 chordomas (Ch), 32 osseous tumors (T. Os) (19 primary and 13 metas tasis) and 15 cases considered as uncommon tumors. (T. Part.) (4 melan omas, 3 hemangioblastomas, 3 dermoid or epidermoid cysts, 2 ependymoma s, 1 cavernoma, 1 angiomyolipoma and 1 cholesterin cyst). Mean age is 47 years, with a sex ratio F/M of 1.511. Duration of symptoms before d iagnosis is of 27 months. Topography is classified into 3 groups anter ior (70 cases), lateral (142 cases) and posterior (24 cases). A partic ular definition is given to these localizations, essentially referring to surgical difficulties and specially for meningiomas. The localizat ion of a tumor is defined by the point of attachment to any structure (dura, spinal root, spinal cord) ; anterior tumors are attached to the F.M. on both sides of the midline ; lateral tumors between the midlin e and the dentate ligament and posterior ones behind the dentate ligam ent. According to this way of classification, N are always lateral eve n if they present anterior or posterior extensions. Most of the cases are intradural (I.D.) (177 cases), but 55 cases are only extradural (E .D.) and 42 are of hour-glass form (I.D.-E.D.). Clinical diagnosis is still frequently erroneous because of the very unusual evolution and c ombination of symptoms commonly observed at the beginning. At the time of diagnosis, the association of focal signs, spinal cord compression signs and signs of involvement of the posterior fossa should easily p ermit to assess the correct diagnosis. The first most common symptoms are posterior headaches (38 %), motor deficit (15 %) and paresthesiae (9 %). However, some cases present, with acute onset or remittent evol ution, with cervico-brachialgia or even sciatica, or with dissociatcd sensory disturbances, amyotrophy, cruciate paralysis... So even in thi s recent series, 13.5 % of cases were misdiagnosed as syringomyelia, s pondylosis, multiple sclerosis, or carpal tunnel syndrome.C.T. scanner and M.R.I. usually permit to finally establish the diagnosis and to p recise the localization and extent of the tumor. Angiography was perfo rmed in 65 % of the cases. Angiography helps appreciate the relation w ith the vertebral artery (12 cases of stenosis and occlusion), and the vascular supply. Results are analyzed using a clinical grading from 0 (no sign), to 5 (dead) ; 1 = single sign or symptom; 2 = minor signs; 3 = marked signs; 4 = bedridden. The average pre-operative grade is 2 .16 turning to 1.33 post-operatively with a mortality of 9.9 %. Worse post-operative results are observed in anterior (1,72) and I.D. tumors (1,60) as compared to lateral (1,17) and posterior (1,14) and to E.D. (1,39) and I.D.-E.D. (1,21). A short chapter deals with the different ial diagnosis and specially with pseudotumor lesions such as synovial cyst, rheumatoid pannus, spontaneous epidural hematoma and thrombosed vascular malformations. The following chapters reported on the three m ain types of tumor (meningioma, neurinoma and chordoma) and on the two groups of osseous and particular tumors. An extensive review of the l iterature permits to discuss the features of each type of tumor. Menin gioma is the most common type of F.M. tumor (70 % of all I.D. tumors o f the F.M.). Psamommatous types are particularly frequent at the level of the F.M. compared to cerebral and spinal M. Anterior localization accounts for 31 % of the cases, lateral for 56 % and posterior for 13 % ; extradural and hour-glass forms are observed in 4 and 10% respecti vely. Results in terms of clinical grading and quality of resection ar e discussed according to the age, the localization, and the relation w ith the cranial nerves and the vertebral artery. Anterior tumors, thos e with an E.D. extension and those extending above and below the verte bral artery, have the worse results (table I) ; however, in these case s, the posterolateral approach helps improve them. In this series, 4 c ases are recurrences already operated on more than 10 years before and 4 cases exhibit a recurrence between 2 and 4 years. The rate of compl ete removal is 77 %. Subtotal and partial resection is realized in 16 % and 7 % respectively. [GRAPHICS] Neurinomas (N) of the F.M. include Cl, C2 and XII cranial nerve N to which must be added the cisternal fo rms of IX, X and XI cranial nerves N. Multiple forms and neurofibromat osis are very frequent ( 17 % and 26 % respectively) as compared to sp inal N in general. According to our classification, all N are lateral, 36.5 % are E.D. and 51.5 % of hour-glass form. Pre-operative clinical grades are similar in N and M. However, post-operative results improv e much more in N than in M (Post-operative grade of 0.8 and 1.52 respe ctively). Postero-lateral approach or a combination of posterior and l ateral approaches is specially useful in cases with an E.D. part. Chor doma (Ch) is the third most common type of F.M. tumor. True F.M. Ch ar e difficult to differentiate from clival Ch. As in all the osseous tum ors, cranial nerves involvement is frequent. This series of