M. Rahmatulla, BDS, MDS, FICD*
Department of Biomedical Dental Sciences, King Saud University College of Dentistry,
P.O.Box 601 69, Riyadh 11545, Saudi Arabia.

 
Two cysts in the maxilla were subjected to routine roentgen imaging followed by CT scanning. Roentgen investigation included periapical, occlusal, and panoramic views. CT imaging included axial and coronal scans. While roentgen views were adequate in establishing the diag­ nosis of the cystic lesions, CT scan was useful in understanding the precise antero-posterior expansion and depth of the lesion. Interpretation of CT scan of cystic jaw lesions without con­ ventional radiographs can be misleading. Hence, the CT procedure may be used only as sup­ plement to the routine radiographic investigations particularly in cystic lesions of the jaws

 
Radiographic examination is a simple and quick diagnostic procedure for jaw lesions. CT scan (X-ray computerized axial tomography) is a diagnostic procedure which found application in neurosurgery soon after its advent in the seventies by Hounsfield.1 Mackenzie et al2 have outlined the principle of CT scan imaging in details. The value of CT in oral surgery has been outlined by Frame and Wake.3 They have emphasized the special value of CT in the diagnosis and assessment of expanding and infiltrating lesions of the jaws specially in the maxilla such as maxillary antrum, nasal cavity or pterygoid space.
Several excellent reports4, 5, 6 on the usefulness of CT scan in thediagnosis and management of maxil­ lofacial pathosis have also appeared.
The main principle of CT is based on the attenua­ tion of fine parallel X-ray beams projected from multiple sources through various parts of the body. The procedure involves passing a pencil beam of X- rays through specified thickness of the body. The detectors measure attenuation of the X-ray beam and transfer the results to a computer. In the CT scan of a skull, the scanner later takes slices at 10 mm intervals through the head and the face. This method allows each slice of tissue to be viewed from above to give unique display. In the case of the maxilla narrow slices (5 mm) parallel to the canthomeatal line are obtained through the inferior part of the maxillary antrum of the hard and soft tis­ sues.
In this paper the role of CT in imaging two cystic lesions of the maxilla is discussed along with con­ ventional radiographic procedures.
Case Reports
Case 1
A 13-year-old male was referred for aesthetic reasons to the Dental Department of Kilpuk Medi­ cal College (KMC) Hospital in Madras, India with a large painless swelling of the left maxilla. The swel- ling had an insidious onset. On examination, the patient had unremarkable general health. Oral examination revealed full complement of teeth and no carious lesions. Palpation of left vestibular reg­ ion revealed a large expansile swelling, cystic in consistency. The hard palate also showed slight expansion.
Roentgen examination included periapical, occlusal, Water's, and panoramic views. The occlusal view [Fig. 1 ] showed a large cystic lesion in the left side of the hard palate with a supernumer­ ary tooth above the roots of the left incisors. Another submerged supernumerary tooth was also vis­ ualized above the apices of the right upper incisors without any secondary lesion. The panoramic view [Fig. 2] showed a large rounded radiolucent lesion above the roots of the incisors and the premolars with a corticated outline. A supernumerary tooth with dilacerated root was seen above the roots of the upper left lateral incisor and the canine. On aspiration, about 10 cc of amber colored fluid was withdrawn.
Based on clinical and roentgen findings, the case was provisionally diagnosed as dentigerous cyst of a supernumerary tooth origin.
Using a CT scan unit (whole body 7020 HP) tomographic scan of the maxillary region was car­ ried out. The tomogroph showed septal deviation of the nose towards the right side with hypertrophy of nasal turbinate and complete obliteration of the nasal canal on the left side [Fig. 3]. The maxillary antrum showed normal appearance on both sides and asymmetric soft tissue swelling in the maxillary area of the left side. The maxilla showed expansion of bone on the left of the midline with its bony wall on the medial and inferior aspect of the hard palate extending to the right midline with destruction of the anterolateral wall [Figs. 4, 5]. Irregular faint dense shadow with two or three tooth like struc­ tures were seen in the anterior aspect of the cystic mass. Inside the cyst, a dense and diffuse homogenous shadow was seen [Fig. 6]. The radiological impression was that of an ameloblas­ toma.
Case 2
A 22-year-old female, in apparent good health, was referred to the Dental Department of KMC Hospital with a left maxillary swelling. The swelling had an insidious onset and had been present for the previous one year only. Recently, prior to her com­ ing to the clinic, she developed pain on the leftside of her face. Examination revealed a non- tender warm swelling of the left maxilla with typical cystic consistency. The left upper central incisor was non- vital [Fig, 7].
Roentgenographic investigation included periapical, occlusal, Water's, and panoramic views. Periapical view showed a large cystic lesion in relation to upper incisors. Water's view showed opacity of the left maxillary antrum. The panoramic view showed opacity in the left maxillary antrum and loss of cortication in the floor of the antrum [Fig. 8]. From the clinical and roentgenographic findings the case was diagnosed as dental cyst related to the upper central incisor.
The patient had both axial and coronal CT scans. There was asymmetric swelling of the left maxillary antrum and left maxillary expansion with thinning of bony wall [Fig. 9] at places in both outer and inner plates. A uniform density with no pockets of air was seen in the left antrum. Coronal scan [Fig. 10] showed that the nasal septum was deviated to the right side. The dense mass extended medially and antero-laterally. Radiologist's impression queried malignancy of the left maxillary antrum. The right maxillary antrum appeared normal.

 
In the first case, occlusal and panoramic views pointed to the diagnosis of dentigerous cyst of a supernumerary tooth origin. Both views showed the latero-medial and antero posterior extents of the cystic lesion. Two supernumerary teeth, one involving the cyst were also seen. The CT scan revealed deviation of the nose and hypertrophy of the turbinate, a finding not observed in the conven­ tional radiograph. Conventional radiographs showed the soft tissue swelling and the displaced tooth more clearly than the CT scan.
In the first case, at the time of aspiration of the cystic lesion, CT scanning was not envisaged. Hence, with the aspiration of the fluid, and the con­ sequent shrinkage of the swelling, the radiologist's impression of ameloblastoma in the CT scan was understandable. CT scanning report of jaw lesions alone, without reference to the conventional radiographs, is not advisable. Nevertheless, the CT image in this case has helped to understand the true antero-posterior extent of the cystic lesion.
In the second case, the conventional roentgen images established the diagnosis of a dental cyst. The CT scan in this case supplemented the informa­ tion gained from the conventional radiographs. Cystic expansion particularly thinning and defi­ ciency of outer and inner boundaries and deviation of the bony septum to the right were some of the findings not visualized in the routine radiographs. The coronal section projected the supero-inferior extent, and the axial scan showed the antero-post­ erior extent of the cystic iesion. The radiologist's impression of malignancy from the CT scan find­ ings alone was accepted with caution. While roentgenographic imaging of cystic lesions in the maxilla, with conventional procedures, were adequate in the diagnosis of the lesion, CT scan imaging was a valuable adjunct in understanding the true extent of soft and bony lesions particularly in the maxilla, which has complex intraosseous bony structures. Obviously, this procedure appears to be distinctly advantageous in planning surgery.

The author wishes to express his sincere gratitude to Dr. K. jagadeesan, Director of Krlpuk Medical College Hospital, Madras for offering the CT scan facilities, Thanks are also due to Dr. C. M. Nandagopal, Oral Surgeon of the Government's Royapettah Hospital, Madras for the surgical management of the cases. Appreciations are also due to Dr. Zohair Haidarfor reviewing the manuscript and other constructive suggestions, Ms. Cora Alano for typing the manuscript, and Mr. Roily Abanto for the excellent photographic reproduction.