Accessory oval foramen

ANNALS OF ANATOMY

Accessory oval f o r a m e n Jelena Krmpoti~-Nemani~, Ivan Vinter, and Dubravko Jal~ovec

Department of Anatomy "Drago Perovid', Salata 11, 10000 Zagreb, Croatia

Summary. We describe an opening with smooth walls in front and medial to foramen ovale which leads to an oblique canal directed towards the fossa pterygoidea. The canal was up to 2.3 mm long and opened near the root of the pterygoid process. We called this opening "foramen ovale accessorium", and found it in 48 of 124 anatomical specimens. The foramen was present in newborns and in those aged over 80 years old on one side but rarely on both sides of the sphenoid bone. Only in a single specimen were there two foramina side by side in front of the foramen ovale. In another case, the foramen ovale accessorium was present in the anterior wall of the canalis ovalis and pointed to the fossa pterygoidea. The localization and direction of the foramen ovale accessorium led us to the conclusion that it housed some of the separate rootlets for the chewing muscles, in this case for mm pterygoidei, mm tensor veli palatini and tensor tympani. The existence and contents of the foramen ovale accessorium is important in surgical interventions on the trigeminal nerve and/or ganglion Gasseri. Key words: Foramen ovale - N. trigeminus - Foramen ovale accessorium

Introduction In several skull bases we found in front and medial to the foramen ovale an eliptic opening with smooth walls leading to a canal which opened on the inferior surface of the skull base. This canal was directed towards the fossa pterygoidea. The localization and the direction of the canal, as well as the data from the literature (1) concerning the multilocular origin of motor rootlets in the region of the pons, permit the conclusion that it contained some

Correspondence to: J. Krmpoti6-Nemanid

I

Ann Anat (2001) 183:293-295

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motor rootlets of the motor portion of the trigeminal nerve, which supply the pterygoid muscles, mm. tensor veli palatini and tensor tympani. We called this opening "foramen ovale accessorium".

Material and methods In order to ascertain the frequency of the foramen ovale accessorium we examined 124 skullbases and/or sphenoidal bones in the life period from the new-born to 80 years of age. We measured the dimensions of the foramen ovale accessorium as well as its distance from the oval foramen.

Data from the literature According to Gudmundsson et al. (1971) the third division of the trigeminal nerve may be situated lateral or caudal to the first division. The motor portion of the third division of the trigeminal nerve when leaving the pons is situated in front of the sensory radix and runs under the triangular portion of the ganglion in cavum trigeminale in the direction of the foramen ovale (3). There exists anastomoses between the motor and sensory part of the nerve (2, 4). According to Gudmundsson et al. (1971) the trigeminal nerve arrises from the pons with motor, sensory and aberrant sensory rootlets. These authors studied the pattern of origin of these rootlets of the third portion of the trigeminal nerve on 50 brains and found that in 49 cases the motor root of the nerve was composed of 4 to 14 rootlets having a separat e exit from the pons. The number and the localization of rootlets varied from specimen to specimen. From 50 brains an average of 8 rootlets in each motor root was found. The diameter of the rootlets varied from 0.1 to I mm. The existence of an accessory foramen ovale was not mentioned in this connection. 0940-9602/01/183/3-293 $15.00•0

Results F o r a m e n ovale accessorium was p r e s e n t on one or on b o t h sides of the s p h e n o i d b o n e (Figs. 1-4). It was situa t e d 1 to 5.5 m m m e d i a l (the distance was 3 m m in average) and rostral to the f o r a m e n ovale. The shape of the f o r a m e n ovale accessorium was oval, and the d i a m e t e r of

the long axis varied from 0.5 to 2.5 ram, (1.1 m m in average). In one specimen, two f o r a m i n a accessoria of 0.5 m m were found side by side. In the rest of specimens f o r a m e n ovale accessorium a p p e a r e d on the right or left side (38 specimens) and very rarely on b o t h sides in the same specimen (Fig. 2 b, 5 specimens). In young individuals the f o r a m e n ovale was not always

Fig 1. a) Foramen ovale accessorium (FOA, arrow) in a newborn (CRL 520 ram). b) Same specimen. Inferior opening of FOA at root of the pterygoid process. Fig. 2. a) FOA on the left and right side (arrows) in a 5 year old child. b) Same specimen. Inferior openings of FOA (arrows) on the inferior surface of the sphenoid bone. Fig. 3. a) FOA (arrow) in a 7 year old child. b) Same specimen. Inferior opening of FOA at the root of the pterygoid process (arrow). Fig. 4. a) FOA (arrow) in a 64 year old individual. b) Inferior opening of FOA (arrow) at the root of the pterygoid process in the same individual. Fig. 5. Hour-glas shaped foramen ovale in a 21 year old individual. The anterior narrower part points to the pterygoid fossa. Fig. 6. FOA (arrow) within the anterior wall of the foramen ovale in a 53 year old individual. 294

completely closed and in some cases it remained open in its posterior part even up to 7 years of age. The foramen ovale accessorium led into a canal with smooth walls directed towards the pterygoid fossa. The inferior opening of the canal was situated on the inferior surface of the spenoidal bone close to the root of the pterygoid process (Figs. 1 b-4 b). In some cases the foramen ovale accessorium was not present but the foramen ovale displayed an hour-glass shape (Fig 5). Its anterior portion was narrower than the posterior one and was oblique and directed towards the pterygoid fossa. In the case of one adult, we found an opening in the anterior wall of the canalis ovalis (Fig. 6) which was also directed towards the pterygoid fossa.

after their exit. We assumed that some of these rootlets did not join the main motor trunk but ran separately to the mentioned muscles. The cases where the oval foramen was hour-glass shaped consisting of an anterior narrower and a posterior larger portion as well as the case where there was an opening in the anterior wall of canalis ovalis might confirm our hypothesis that the foramen ovate accessorium lodged the motor branches of the trigeminal nerve which did not join the motor root but remained separated from their exit of the pons to their destination. The presence of the foramen ovale accessorium is important for surgical interventions in the region of the trigeminal nerve and ganglion of Gasser.

References Discussion The oblique canal running through the skull base began on the inner surface of the skull and ended on its inferior surface close to the root of the pterygoid process. A wire pushed through the canal pointed to the pterygoid fossa. Its superior opening was situated 1.3 mm in average in front of the foramen ovale. The vicinity to the foramen ovale and the direction of the canal towards the pterygoid fossa led us to the conclusion that the canal contained the neural branches for the pterygoid muscles as well as branches for m. tensor veli palatini and m. tensor tympani. Goodmundsson et al. (1971) found that the motor rootlets leave the pons as separate branches which unite

Wilson-Pauwels L, Akesson EJ, Stewart PA (1988) Cranial nerves, anatomy and clinical comments. B.C. Decker Toronto, Philadelphia Gudmundsson K, Rhofon AL Jr, Rushton JG (1971) Detailed anatomy of the intracranial portions of the trigeminal nerve. J Neurosurg 35:592 Lanz T von, Wachsmuth W (1979) Praktische Anatomie. Bd I, Kopf. Springer Berlin Heidelberg New York Vidid B, Stefanatos J (1968) The roots of the trigeminal nerves and their fiber components. Department of Anatomy, Saint Louis University, St. Louis Missouri.

Accepted December 27, 2000

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