D URING the study of a fairly large material of microscopical sections of

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1 ARACHNOIDAL PROLIFERATIONS WITH CYST FORMATION IN HUMAN SPINAL NERVE ROOTS AT THEIR ENTRY INTO THE INTERVERTEBRAL FORAMINA PRELIMINARY REPORT BROR REXED, M.D. Department of Histology, Karolinska Instituter, Stockholm, Sweden (Received for publication March 28, 1947) D URING the study of a fairly large material of microscopical sections of human spinal nerves and nerve roots, the author noted in some of them certain remarkable alterations of the structures. The alterations consisted of a more or less intense proliferation of the root arachnoidea. As is well known, the dural and arachnoidal sheaths are restricted to the entrance into the intervertebral foramina. In some roots these arachnoidal proliferations were connected with cysts in the roots themselves. Since a search through the current literature revealed no description of th~s condition, the author decided to investigate it. The present paper is a report of the findings so far made. MATERIAL AND METHODS The material always consisted of the lumbar spinal cord with its nerve roots and the first stretch of the spinal nerves enclosed in the dural sac. It was taken at post mortem, 6-36 hours after death. The patients were aged from 80 to 80 years. They all died from illnesses not affecting the nervous system. The cord and nerves had been fixed in 10 per cent formaldehyde solution for more than a year previous to the histological examination. Spinal nerves and roots from 44 segments of the spinal cord of 17 cases were studied. Parts of the nerve roots near the spinal cord from all the segments were stained according to the Alzheimer-Mann-HKggqvist (AMH) method (see Rexed 4) or impregnated with silver according to Bodian. The nerve roots near the spinal ganglion, the ganglion and the first stretch of the spinal nerve from each segment were sectioned serially. Series from alternating segments were stained by the AMH and the Bodian technique. In the Bodian stained series sections were spared at regular intervals and stained with the Azan or the hematoxylin- Weigert-Hansen stain. The above material was originally assembled for the study of the effects of lateral disc protrusions on nerve roots and spinal nerves and will be more fully accounted for in a paper to be published shortly on this subject by Lindblom and Rexed. RESULTS When the spinal nerve roots entering the intervertebral foramen converge, they are enclosed for a short stretch by tubular sheaths of the dura mater. These sheaths come in contact with the nerve roots and fuse with their connective tissue just above the spinal ganglion. Thus a small, funnelshaped space is formed around each root on its entry into the intervertebral foramen (Fig. 1). The arachnoidea dips into this space and surrounds the root with a loose cover. 414

ARACHNOIDAL PROLIFERATIONS IN NERVE ROOTS 415 Normally the arachnoidal folds around the roots in this space are very sparse and loose, and they fill only part of the space, leaving the rest as an

2 ARACHNOIDAL PROLIFERATIONS IN NERVE ROOTS 415 Normally the arachnoidal folds around the roots in this space are very sparse and loose, and they fill only part of the space, leaving the rest as an empty room between the root and the dura mater. Microscopically the space is seen as a thin slit around the root, occupied only by a very loose and thin fold of arachnoidea. In a certain number of cases, however, the picture is quite different. The change when least developed consists of a moderate thickening and increase in amount of arachnoidal tissue around the roots. In some other cases the arachnoidal folds are still thicker and at circumscribed areas have the ap- FIG. 1. Half-schematic drawing of the relationship between meninges and spinal nerve roots in man (cervical region). Note subdural space around spinal nerve roots at entrance into intervertebral foramen (right side of drawing). The drawing is not exact in details, however: the separate dural sheaths for dorsal and ventral roots and arachnoidea, following dura towards ganglion, are not shown. (From Rauber and Kopseh:~.) pearance of definite proliferations, pressing on the roots and deforming them seriously. In certain places the arachnoidal proliferations invade the interior of the root fascicles and form cyst-like cavities which stand in open connection with the space around the root. The tissue inside the cyst is in direct continuity with the thickened arachnoidal folds outside. In most cysts only the wall of the cyst is coated with the proliferated tissue while the center of the cyst is empty (Figs. 7, 15 and 16). There thus exist all gradations from a just perceptible increase in the volume of the arachnoidea in the dura-surrounded space around the roots to intense proliferations with strong deformations and cyst formation in the roots. A full report of these findings will follow in the final publication,

3 416 BROR REXED

4 ARACHNOIDAL PROLIFERATIONS IN NERVE ROOTS 417 when a larger material can be presented; for further details see the figures and their legends. A striking fact is, however, that not even the most affected roots show any sign of acute processes of any kind. The appearance of the arachnoidal proliferations is definitely that of static or resting tissues. There are no signs of acute inflammation or of neoplastic processes. The affected root fascicles and their nerve fibres show no sign of damage (except, of course, for the deformation of the fascicles in toto and by the proliferated tissue and the cyst), and no degenerating nerve fibres have been seen. Proximally and distally to the cysts the root fascicles have an absolutely normal appearance. Small islands of tissue of the kind described above can be seen not only in the roots but also in the dense dural sheath surrounding the roots (Fig 18). The condition described was never found elsewhere than in the short stretch of the nerve roots passing through the dura-enclosed funnel-shaped space just proximal to the spinal ganglion. It was never observed near the spinal cord or in the free part of the root crossing the subarachnoidal space between spinal cord and intervertebral foramen. Counting only the cases with fairly severe changes, 8 cases out of 17 examined showed the described condition in one or more segments. When the nerve roots of one side of a spinal segment showed the condition, this was usually also the case with the roots of the other side and with roots from other segments. The material hitherto examined is far too small, however, to allow definite conclusions concerning general frequency, distribution of the condition, etc. DISCUSSION On account of the smallness of the material only the most summary discussion is worth while. Though all the persons from whom material for this study was taken were affected by lateral disc protrusions, it is highly improbable that the above-described condition has anything at all to do with that abnormality. Abnormal araehnoidal proliferations were found just as commonly in segments and roots of individuals not affected by lateral disc protrusions. Besides, the lateral disc protrusion does not compress the nerves more proximally than at about the middle of the spinal ganglion and most often nlore distally to the ganglion on the spinal nerve itself. The type of changes result- Fins Arachnoidal proliferation with cyst formation, shown in a series of microphotographs (Fig. 9 is most distal section). Right ventral root from ~nd lumbar segment. Case K.~2'24-48 (67 years old). In Fig. ~ the funnel-shaped space around the root shows as a thin slit, filled with some arachnoidal folds, and bounded by a dense ring of dural tissue. In Figs. 3-6 a proliferation of the arachnoidea compresses the root more and more, till its contour looks like a half-moon. In Figs. 7 and 8 the proliferation is completely surrounded by the nervous tissue. In Fig. 9 the cyst has terminated, leaving only a slight irregularity in the texture of the root. AMH stain; magnification varying between least in Figs. 4-6.

5 418 BROR REXED

ARACHNOIDAL PROLIFERATIONS IN NERVE ROOTS 419 ing from compression of nerves by disc protrusion is different (this statement will be well substantiated in the paper by Lindblom and Rexed~).

The same can be said about the possibility of neoplastic growths. Neither are there any signs of acute inflammatory processes.

6 ARACHNOIDAL PROLIFERATIONS IN NERVE ROOTS 419 ing from compression of nerves by disc protrusion is different (this statement will be well substantiated in the paper by Lindblom and Rexed~). There is a possibility that the cystic formations can be traced back to some developmental disturbance, but so far nothing has been brought forward that supports such a theory. The same can be said about the possibility of neoplastic growths. Neither are there any signs of acute inflammatory processes. It is possible, however, that the condition is the terminal result of such an inflammation already healed, or that it is in itself a very slow chronic process. The well known pathological condition arachno:diti.s' spinalis adhaesi~,a circumscripta el cystica might be the macroscopic counterpart to the microscot)ic changes described in this paper. As shown by Oseki,"- meningitic reactions without clinical manifestations are often seen in F,G. 15. Large cyst in left ventral root many general infectious diseases. At from 5th lumbar segment. S.S3-4~2 (8i years present, at any rate, it seems impossible old). The nervous tissue of the root forms only 9 a thin shell around the cyst. Note mass of to exclude the possibility that such debris inside. Bodian stain; X50. meningitic inflammatory reactions might result in changes, such as those described above. The clinical importance of the condition is equally difficult to evaluate. The life-history of the investigated cases was not known in sufficient detail to allow any conclusion in this respect. Naturally the development of arachnoidal proliferations of the severity seen in some of the cases must give symptoms from the affected roots. It seems clear, moreover, that a nerve root thus affected must be a locus minoris resistentiae. There is an intimate relation between the thickened arachnoidal tissue and the nerve fibres of the root. In the case of a new inflammatory meningitic reaction, even a mild swelling of the arachnoidea would affect the root fascicles in the cramped space in the dural sheaths and give rise to symptoms of a radiculitis. It seems that one could not exclude the possibility that some such mechanism might be the cause of certain cases of sciatica with obscure etiology. The same mi~'ht be the case with other inflammatory states of the nerve roots. FIGS Araehnoidal proliferation with deformation of left dorsal root from ~nd lumbar segment, shown in a series of microphotographs. Case K.~ The fairly large p[oliferation takes up much room inside the doral s:math and pushes the root to one side. In Fig. 14 the beginning of the spinal ganglion is marked by the appearance of a cluster of nerve cells. AMH stain; X50.

7 4~0 BROR REXED Fro. 16. Small cyst in left ventral root from segment in Case K.~ Note delicate wall of the cyst and sound appearance of the adjacent nerve fibres. AMH stain; KS0. FIG. 17. Small cyst in right dorsal root from ~nd segment in Case K.~4-43. AMH stain; N65.

8 ARACHNOIDAL PROLIFERATIONS IN NERVE ROOTS 4~1 Fro. 18. Proliferated araehnnidal tissne penetrating the dense dura mater. AMH stain; )<80. SUMMARY Around human nerve roots on their entry into the intervertebral foramina there has been found in some cases a pathological thickening and proliferation of the arachnoidea. These circumscribed proliferations resulted in the most extreme cases in severe deformation of the nerve roots and were connected with cystic formations in the root fascicles themselves. The etiology and importance of the condition is discussed. REFERENCES 1. LINDBLO~, K., and REXED, B. [To be published.] ~. OSEKI, S. ~ber makroskopisch latente Meningitis und Encephalitis bei akuten Infektionskrankheiten. Beitr. path. Anat., 191~, 52: RAtTBER, A., and KOPSCH, F. Lehrbuch und Atlas der Anatomic des Menschen. Leipzig: G. Thieme, 1930, lsth ed., 5-6:607 pp. 4. REXED, B. Contributions to the knowledge of the postnatal development of the peripheral nervous system in man. A study of the bases and scope of systematic investigations into the fibre size in peripheral nerves. Acta. psyehiat., Kbh., 1944, supp. 33, 1-~06.

Synovial cyst of spinal facet

Synovial cyst of spinal facet Case report CHUN C. KAO, M.D., STEFAN S. WINKLER, M.D., AND J. H. TURNER, M.D. Sections of Neurosurgery, Radiology, and Pathology, Madison Veterans Administration Hospital, and University of Wisconsin,