The neglected maxillary process of the palatine bone

ANNALS OF ANATOMY

The neglected maxillary process of the palatine bone Jelena Krmpoti~-Nemani~, Ivan Vinter, Zlatko Kelovi~, and Slaven Suknai~ Departement of Anatomy, Medical Faculty, University of Zagreb, Salata 11, HR-10000 Zagreb, Croatia

Summary. In most recent anatomy textbooks as well as in the latest anatomical nomenclature, the maxillary process of the palatine bone is not mentioned at all. The maxillary process is, however with rare exceptions, always present as an important part of the closure of the hiatus sinus maxillaris. In our material consisting of 200 disarticulated, macerated skull bones and 25 specimens of maxillary sinus, the maxillary process was missing in only 5 cases (2.2%). This process develops in the second year of life and displays different shapes. It can be long and slender or wide and round shaped. Its upper margin is more or less concave, corresponding to the margin of the hiatus over which it is bent. Its inferior margin can be smooth or irregular. In instances in which maxillary sinus is double, the os palatinum has two maxillary processes, so that both sinuses are partly closed with the maxillary process of the palatine bone. Key words: Maxillary process of palatine bone - Hiatus sinus maxillaris

Introduction The constituents of the palatine bone and thus the bony closure of the hiatus sinus maxillaris were not correctly interpreted in the penultimate (1970), nor in the last (1998) anatomical nomenclature and in anatomy textbooks, compared with the classical anatomical data. According to the classical anatomical data the following elements take part in the closure of the hiatus sinus maxillaris: anteriorly the lacrimal bone, from above the uncinate process of the ethmoid bone, below the maxillary and ethmoid processes of the inferior concha and posteriorly the maxillary process of the palatine bone.

Correspondence to: J. Krmpotid-Nemanid Ann Anat (2003) 185:53-56 © Urban & FischerVerlag

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In the recent anatomical nomenclature (1998) only the nasal process is listed and it is hence considered the only constituent of the posteroinferior limit of the hiatus sinus maxillaris. The aim of our study has been to determine the frequency of appearance of the maxillary process of the palatine bone, its relation to the lateral side of the medial wall of the sinus maxillaris, as well as its relation to the maxillary process of the inferior turbinate.

Material and methods We investigated the nasal and the maxillary process of the palatine bone in 200 disarticuiated skull bones from fetal life (CRL 200 mm) to the newborn and from the newborn to 30 years of age. We also examined 25 specimens of the nasal cavity where the maxillary sinus was exposed from the lateral side by the removal of the zygomatic process of the maxilla. The material was autopsy material belonging to the caucasian ethnic group. The age and sex of the specimens was always primarily dated.

Data from the literature In some anatomy textbooks [1, 3, 5, 6, 7, 10, 27, 28, 30], even the nasal process is omitted in the description of the constituents closing the hiatus sinus maxillaris. We found the most detailed description of the maxillary process of the palatine bone in the publication of Elze (1913) who named this process, and the causal explanation of its development or of its possible absence in the monography of Perovid (1954). Because of its specific shape, Schultz (1852) gave this process the name "processus semilunaris" and because of its close relation to the nasal wall of the maxillary corpus and the maxillary process of the inferior concha the name "connexus imbricatus". The shape and the length of the processus maxillaris varies from specimen to specimen, but it is always present at the beginning of the second year of life. This process is 0940-9602/03/185/1-53 $15.00•0

always partly covered by the maxillary process of the inferior turbinate. The name °'processus maxillaris" was given at the suggestion of Elze included in Toldt's "Anatomischer Atlas (1914)" where it appeared in the 8 th to the 27 th edition (Toldt-Hochstetter 1979). The nasal and/or the maxillary process was described in classical anatomies. Hyrtl (1863) described a thin, triangular processus, originating from the anterior margin of the vertical plate of the palatine bone, which narrowed the maxillary sinus. Henle (1871) described the maxillary process as the nasal process of the palatine bone which joined the hiatus and sometimes was bent over the lateral side of the sinus maxillaris. Graf v. Spee did not mention the nasal and/or the maxillary process of the palatine bone. However the illustration of the lateral side of the vertical plate displayed a prolongation which could be identical with the nasal process. In the Anatomy of K. v. Bardeleben (1906) the name processus maxi!laris was mentioned as the continuation of the vertical plate of the palatine bone which narrowed the hiatus. Merkel (1915) described it as processus nasalis and so did Cruveilhier (1877) and Sappey (1867). Testut (1920) described a prolongation of the anterior border of the vertical plate of the palatine bone which could be identical with the nasal process. Schlungbaum (1921) described not only the mentioned maxillary process but also the processus maxillaris posterior ossis palatini which closed the hiatus sinus maxillaris of the posterior, or secondary, maxillary sinus. Sieglbauer (1935) described the maxillary

process as the "second" process besides the nasal process. According to Perovid (1954) the processus maxillaris of the palatine bone represented the lateral prolongation of the nasal process bent over the medial wall of the maxillary sinus. The maxillary process was described also in Braus-Elze (1956). In Benninghof's Anatomy revised by Goerttler (1968) the processus maxillaris was mentioned as a plate hanging over the border of the hiatus sinus maxillaris. In Lang (1988) the process was clearly represented within the maxillary sinus covered by the maxillary process of the inferior turbinate. French authors: Le Double (1903) and Augier in Poirier-Charpy-Nicolas (1931) did not mention the nasal and/or the maxillary process of the palatine bone. In his anatomy, Rouvi~re (1974) did not merely mention the maxillary process, but he represented it in the illustration of the palatine bone. Sobotta (1977) represented the maxillary process in the illustration of the palatine bone.

Results The processus maxillaris of the palatine bone (Figs. 1-3) was regularly present with the exception of 5 specimens in all of the examined specimens of macerated disarticulated skull bones and in all except one of the examined nasal cavities. The specimens where the maxillary process was missing belonged to the individuals in the third year

Fig. 1. Maxillary process of the right palatine bone in a 20 year-old individual, lateral view. Fig. 2. Maxillary process of the left palatine bone in a 25 year-old individual, lateral view. Fig. 3. Large right maxillary proces in a 11 year-old individual, medial view. Fig. 4. Large nasal process in a 3 year-old child. The process was not continued by the maxillary process. Right side, medial view.

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of life. In these five specimens the nasal process of the palatine bone was longer than usual (Fig. 4). In all other examined specimens the maxillary process was present and partly covered by the maxillary process of the inferior turbinate (Figs. 5, 6, 7). In the cases where a maxillary process was developed, the posteroinferior region of the hiatus had a triple or quadruple wall: in the mediolateral direction it consisted of the vertical plate of the palatine bone, the posteroinferior margin of the hiatus belonging to maxilla, the maxillary process of the palatine bone and partly the maxillary process of the inferior turbinate cov-

ering the maxillary process of the palatine bone. In all these cases the maxillary process of the inferior turbinate was of usual shape and displayed usual dimensions. The maxillary process of the palatine bone displayed different shapes, it was long and slender or wide and rounded. Its superior margin was mostly smooth and concave, following the shape of the hiatus sinus maxillaris, whereas its inferior margin was often irregular (Figs. 1-3, 5-7). In cases where the nasal process was longer than usual, it did not bend over the margin of the hiatus to be continued as the maxillary process but proceeded in its growth anteriorly to reach the maxillary process of the inferior turbinate. The maxillary process of the inferior turbinate was much smaller than usual in these specimens. The maxillary process of the palatine bone could be demonstrated in its whole shape in the specimens where the maxillary sinus was opened by the removal of the zygomatic process of the maxilla (Figs. 5-7). In these specimens, it was evident that the maxillary process played an important role in closure of the hiatus sinus maxillaris. In cases of the double maxillary sinus (type of Schlungbaum) the palatine bone had two maxillary processes (Fig. 7) which partly closed the hiatus in both sinuses.

Discussion The relation of the maxillary process of the palatine bone to the maxillary process of the inferior turbinate has its origin in the primitive nasal capsule. The nasal capsule displays a medial inflexion on its inferior margin, the future origin of the inferior concha. The inferior concha ossifies by enchondral ossification as the first bone of the lower visceral skeleton. This happens, according to Augier (1931) and Perovid (1954), already in fetuses of 117 mm CRL. The processus is completely ossified already in the newborn. The rest of the bones (maxilla and os palatinum) encircling the maxillary sinus ossify much later by membranous ossification. The processus maxillaris of the inferior concha is thus the first osseous part of the future bones encircling the maxillary sinus. The position of both maxillary processes depends upon the development of the maxillary sinus. At the beginning of the development of the maxillary sinus, the maxillary process of the palatine bone closes with perpendicular to its plate, an angle of 90 degrees. This relation changes due to the development of the maxillary sinus, which becomes deeper. The maxillary process of the palatine bone and that of the inferior turbinate follow the lowering of the bottom of the maxillary sinus due to dentition. In the developed maxillary sinus both processes lean against the medial wall of the sinus. In this position the maxillary process of the palatine bone is covered by the maxillary process of the inferior turbinate. If the maxillary process of the inferior turbinate was underdeveloped, the nasal process proceeded its growth anteriorly to the maxillary process of the inferior concha and formed, without bending into the maxillary

Fig. 5. Maxillary sinus after the removal of the zygomatic process. Maxillary process is framed by a black line. Adult individual, left side. Fig. 6. Maxillary sinus after the removal of the zygomatic process. Maxillary process is encircled by a black line. Adult individual, right side. Fig. 7. Double maxillary sinus after removal of the zygomatic process. Palatine bone sends in both sinuses its maxillary process, indicated by a black line. 55

process, the p o s t e r o i n f e r i o r limit of the hiatus sinus maxillaris. In such cases the processus nasalis was e x r e m e l y long. It is the r e a s o n why Perovid (1954) considered the maxillary process of the palatine b o n e as a p r o l o n g a t i o n of the nasal process b e n t over the m a r g i n of the hiatus. W h e n the growing nasal process of the palatine b o n e reaches in n o r m a l conditions the a l r e a d y ossified maxillary process of the inferior concha it is b e n t over the margin of the future maxillary sinus and p r o c e e d s on its way, as the maxillary process, u n d e r the a l r e a d y ossified maxillary process of the inferior concha. The primitive nasal capsule d e t e r m i n e s thus the direction in growth of the m e m b r a n o u s bones, which a p p e a r much later. E v e n if some authors consider the maxillary process of the p a l a t i n e b o n e as the p r o l o n g a t i o n of the nasal p r o cess, the maxillary process should be i n t r o d u c e d into the a n a t o m i c a l n o m e n c l a t u r e b e c a u s e it a p p e a r s as such in m o r e than 97% of cases and represents a constant entity. In special cases of d o u b l e sinus maxillaris (type of Schlungbaum) the p a l a t i n e b o n e d i s p l a y e d two maxillary processes: one taking p a r t in the closure of hiatus of the a n t e r i o r maxillary sinus, c o m m u n i c a t i n g with the m i d d l e nasal m e a t u s and the s e c o n d taking part in the closure of the hiatus of the p o s t e r i o r maxilary sinus, c o m m u n i c a t i n g with the s u p e r i o r nasal meatus. The processus maxillaris p o s t e r i o r of the palatine b o n e o r g i n a t e d b e l o w the sphenoidal process of the palatine bone. This process was also p a r t l y c o v e r e d with the maxillary process of the m i d d l e nasal concha which j o i n e d the m e d i a l wall of the secondary maxillary sinus in a special type of c o n n e c t i o n called " h a r m o n i a " . It should be n o t e d that it is e x t r e m e l y difficult to save the maxillary process during the m a c e r a t i o n and disarticulation of the skull bones in individuals o l d e r than 10 years of age, which might explain its absence in the description of the p a l a t i n e bone. W e think that it was necessary to draw attention to the hiatus sinus maxillaris and to the e l e m e n t s surrounding it b e c a u s e the maxillary sinus is, besides the e t h m o i d a l labyrinth, one of the most diseased sinuses and frequently involved in surgery [29]. Of special interest for the rhinologist is the m e d i a l wall of the maxillary sinus as the site of nasal polyps.

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