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Unilateral Mastoid Hypertrophy

Raymond E. Parks 1

Radiographic demonstration of the mastoid ai r cells has ious ancestors that served a respiratory or flotation function. revealed great variability in th e size and number of air cell s Phylogenetically, all vertebrates have air or water surround­ present. Very rarely, mastoid cell development has been ing their auditory apparatus. excessive with air cell s extending into the occipital as The air cell s of the middle are underdeveloped at the far posterior as th e midline. An example of unilateral hyper­ time of birth, and further development continues through trophy of mastoid air cell development is described. infancy and early childhood. Before birth these tiny cells, as well as the external and , are filled with a gelati­ nous fluid that is progressively displaced by air after birth. Case Report The absorption of the fluid and replacement by air occurs in A 34-year-old man lacerated his forehead and was brought to the external and middle ear of the neonate within hours after the emergency room. films (figs. 1 A and 1 B) showed small birth as a result of crying, swallowing, and movement. and large radiolucent, air-containing cell s extending from the upper However, the air displacement of the numerous mastoid posterior region of the mastoid area on the left sid e, across th e cells is a progressive growth process that probably takes temporal-occipital suture into th e squamous portion of the occipital months or years to be accompli shed, and it probably contin­ bone, and into the posterior part of the . The septa of ues until skull bone growth is complete. the numerous air cell s were deli cate and showed no evidence of Radiographs of children and adults show a wide variation thickening. The cell s measured 2- 30 mm . Th e mastoid air cell s on in the degree of air-cell development. The consensus of the opposite (right) side were well developed, of normal size, and showed no extension beyond the tem poral bone. opinion today supports the theory that auditory air-cell de­ The patient's history was completely negative and the physical velopment is a genetic message, but that infection in infancy examinati on was negati ve. Computed tomography (CT) (figs. 1 C or early childhood may arrest development or obliterate and 1 D) showed extern al symmetry of the skull. It showed that the celi s. The cause for overdevelopment of auditory air cells excessive air-cell development caused in ward displacement of the has not been studied; nothing is known about it nor have inner table of th e sku ll wi th encroachment of th e upper posterior any theories been proposed. There have been a few reports fossa and supratentorial region of th e left posterior calvari a. The of overgrowth of [3, 4], but no report of lumen of th e air cell s contained gas with a CT atten uati on value of unilateral hypertrophy similar to this case could be found in - 1,000 Hounsfi eld units (H). The in ward displacement of the left th e literature. It is of interest that the air-cell development of occipital lobe area caused 1.0 mm of displacement of the pineal gland to the ri ght of th e midline. Th ere was no displacement or this case was halted at the midline of the , deformity of the ven tricular system of th e brain , but the quadrigem­ suggesting its proliferation was by some inherent design inal cistern (cistern of Galen ) had minimal flattening of its left lateral and not as a pathogenic consequence. border. The diploic space between th e internal and extern al tables This case of unilateral hypertrophic development of mas­ of the skull was widest in the occipital squamous region where it toid air cell s apparently produced no symptoms or physical measured 20 mm . findings and was probably a normal growth variant. The pati en t re mained well during a year of foll ow-up.

REFERENCES

Discussion 1. Anson BJ , Donaldson JA. Surgical anatomy of the and ear. Philadelphia: Saunders, 1973 : 1 7 - 29 The function of the mastoid air cells is unknown. One 2. Best TH , Anson BJ . The temporal bone and the ear. Springfield , theory is that th e air cell s serve as some type of resonating IL: Th omas, 1949: 303- 306 chamber for ; another th eory is that they might serve 3. Madeira JT, Summer GW. Epidural mastoid pn eumatocele. as an air-pressure-regulating mechanism for the middle ear; Radiology 1977;122 :727-728 but th e consensus of opinion [1 , 2] is th at the mastoid is an 4. Nomura Y, Takemoto K, Komatsuzaki A. Th e mastoid cyst: embryologic vestigial gill organ from our aquati c or amphib- report of a case. Laryngoscope 1971 ;81 : 438-446

Received April 2, 198 1: accepted aft er revision November 2, 1981. , Department of Rad iology, School of Medicine, TB 134, University of Cali fornia, Davis, CA 9561 6.

AJNR 3:196-197, March/ April 1982 0 195- 6 108/ 82/ 0302-0196 $00.00 © American Roentgen Ray Society AJNR:3, Marchi April 1982 PARKS 197

A B

Fig. 1.-A and B, Plain radiographs: hypert rophic developmenl of lefl masloid air cell s with norm al development of right masloid . A, Left laleral view. Extensive air-cell development ex lends into occipilal and pari elal adjacent to lambdoidal suture. Cells va ry in size from 2 10 30 mm . B , Anleroposlerior (Towne) view. Air cell s in occipital and parielal bone above level of lenlori um extend 10 midlin e posleriorl y. C and D, CT images of skull wilhoul conlrast. C, Scan th rough dorsum sell a and pelrous ri dges (aboul 20° _ 25° angulati on from baselin e). Hypert rophic developmenl of lell masloid air cell s compared wilh opposite side. Fourlh ventricle neil her displaced nor deformed. D, Scan 2 cm higher passing Ihrough anterior pari of laleral venlricles, pineal gland, and upper occipilal bone above tenlorium. Preser­ vation of ouler conlour of skull and norma l thickness of ouler table of skull. Inner lable thinned and displaced inward wilh encroachment on lell occipilal lobe of brain. Pineal gland calcificalion displaced 1.0 mm . c D