Department of Dental Radiology and Radiation Research. Faculty of ... University. Tokyo. Japan ... appropriate for plunging ranulas l-fl where excision of the cyst ...
Differential diagnosis of submandibular cystic lesions by computed tomography T. Kurabayashi, M. Ida and T. Sasaki Department of Dental Radiology and Radiation Research. Faculty of Dentistry. Tokyo Medical and Dental University. Tokyo. Japan
Received 26 February 1990 and in final form 18 September 1990 A retrospective analysis of 35 submandibular cystic lesions was undertaken to assess the usefulness of CT in their differential diagnosis. Lesions were analysed on the basis of extent, shape and density. It was found that all those lesions that extended into both the sublingual and the anterior part of the submandibular spaces could be diagnosed as ranulas (10/10) and all those limited to the posterior part as lateral cervical cysts (8/8). Those lesions that extended to the sublingual, but not the anterior part of the submandibular space, were dermoid cysts if they had a smooth margin (2/2), and probably ranulas when it was concave (4/5). Those lesions that extended into the anterior part of the submandibular but not the sublingual space were ranulas on the basis of a multilocular or concave margin (3/3), but if they had a smooth margin (317) they could not be differentiated from dermoid cysts (417). Although CT density was less valuable for the differential diagnosis, both ranulas and dermoid cysts could be excluded if it was similar to that of muscle. Keywords: Tomography, X-ray computed; mouth floor; cysts, ranula
Several types of cystic lesions, such as ranulas, dermoids and lateral cervical cysts, are found which cause swelling in the submandibular region, but their differential diagnosis on the basis of the clinical signs and symptoms alone is difficult I. It is important to be able to differentiate them prior to surgery, because the surgical approach to each is different. An extra-oral approach is the preferred method for dermoid and lateral cervical cysts, whereas an intra-oral approach is appropriate for plunging ranulas l-fl where excision of the cyst itself is not necessarily required r". The purpose of this retrospective study was to evaluate the usefulness of CT in the differential diagnosis of these cystic lesions.
Materials and methods CT images of 35 cystic lesions in patients who had presented with a non-inflammatory swelling in the submandibular region were analysed retrospectively. The histopathological diagnosis established following surgery was plunging ranula in 20 cases, dermoid cyst in seven (four dermoid and three epidermoid), and lateral cervical cyst in the remaining eight. The age distribution of the patients is shown in Table L They all had swelling in the submandibular region, but, in addition, sublingual swelling was present in 10 out of 20 ranulas and three out of seven dermoid cysts. Most of the lesions were soft or elastic, but three out of seven dermoid cysts and one out of eight lateral cervical cysts were harder. Four ranulas, one dermoid cyst and three lateral cervical cysts had been treated elsewhere, but in all these cases, the swelling recurred prior to CT
Table I Age distribution of the patients
Age (yr) 0-9 10-19 20-29 30-39 40-49 50-59 Total
Ranula (no.) 4 I II
4 0 0 20
Dermoid cyst (no.)
Lateral cervical cyst (no.)
0 3 2 0 I
0 2 0
1
4
7
8
I I
examination. CT was performed with a TCT-60A scanner (Toshiba Medical, Tokyo) at 120kV and 200 rnA. Two millimetre thick axial scans parallel to the lower border of the mandible were obtained at 510 mm intervals through the lesions with a scan time of 9 s per slice. The density, extent, and shape of the lesion on the CT images was assessed as follows: Density
For each case, the CT image showing the widest extent of the lesion was selected and the region of interest (ROJ) was inscribed as a circle with largest diameter and the average CT number measured in Hounsfield units (HU). CT images with apparent artefacts were excluded. Extent
On an axial CT image of floor of the mouth, the mylohyoid muscle can be identified as an oblique mass
© 1991 Butterworth-Heinemann for 30
Dentomaxillofac, RadioL, 1991, Vol. 20, February
0250-832 x 91/0 10030-05
IADMFR
CT diagnosis of submandibular cystic lesions: T. Kurabayashi et al. (1) Lesion with a round or oval shape with a smooth margin on all CT slices. (2) Lesion with a concave margin on one or more CT slices. (3) Multilocular lesion: lesion with more than two cysts on one or more CT slices.
Results Density All the lesions were homogeneous on CT. The distribution of average density is shown in Table II. The CT density in all ranulas and dermoid cysts ranged from + 10 to 39 HU, which was lower than that of muscle (about +60 HUf. There was no difference in density between ranulas and dermoid cysts. Six out of the eight lateral cervical cysts were in the same density range as ranulas and dermoid cysts, but two were higher, and more like that of muscle (Figure 4). The variation in density was largest for the lateral cervical cysts,
Extent The cysts are classified as in Table III. All the lateral cervical cysts were type I and the dermoids were either type II or III. Ten out of 20 ranulas were type IV and the others either type II or III, Figure 1 Diagrammatic representation of the floor of the mouth on an axial CT scan. A. sublingual space; B. anterior part of submandibular space; C. posterior part of submandibular space; a, mylohyoid muscle; b. submandibular gland; c, genioglossus muscle; d, mandible; e , pharyngeal cavity; f. cervical vertebra
that extends from the midline anteriorly backwards and outwards. The submandibular gland area can be subdivided into the following three spaces in relation to the mylohyoid muscle (Figure 1): A - sublingual space: the space between the mylohyoid and the genioglossus muscles just above and medial to the former. B - anterior part of the submandibular space: the space just under and lateral to the mylohyoid muscle. C - posterior part of the submandibular space: the space posterior to the mylohyoid muscle. Lesions were classified into the following four types according to the area occupied (Figure 2): Type I
- lesion limited to the posterior part of the submandibular space. Type II - lesion extending into the anterior part of the submandibular, but not the sublingual space. Type III - lesion extending into the sublingual, but not the anterior part of the submandibular space. Type IV - lesion extending to both the sublingual and the anterior part of the submandibular spaces.
Shape Lesions were classified into the three types (Figure 3):
Shape Table IV shows the classification by shape. All the lateral cervical cysts were round or oval with smooth margins, as were six dermoid cysts. Only three ranulas had a smooth margin and the others were either partly concave or multilocular. The correlation between extent and shape of lesions is shown in Table V. All ranulas with a smooth margin were type II. One dermoid cyst with a concave margin was type III.
Discussion Density The CT density reflects the contents of the lesion. Ranulas usually result from extravasation of saliva into the surrounding tissue 1,2 and their contents are similar to that from the sublingual gland x. In our study, all the ranulas were homogeneous with an average density lower than that of muscle. Dermoid cysts derive from ectodermal tissue trapped during embryonic development 9-1 1 ; those with skin appendages on their capsules are termed dermoid and those without epidermoid, but the former is retained as a clinical term for both types 9, 10. Dermoid cysts may contain a cheesy material mixed with sebaceous gland secretions and keratin 9.12. Several authors have reported that dermoid cysts are heterogeneous on CT, consistent with their variable content 13-15. In particular, Coit et al. 13 reported that all dermoid cysts demonstrated an inhomogeneous appearance on CT images. In contrast, our seven cases were all homogeneous and we could not differentiate them from ranulas on the basis of their density. Nonetheless, we would agree it may be possible to distinguish dermoid cysts sometimes if they Dentomaxillofac. Radiol., 1991, Vol. 20, February
31
CT diagnosis of submandibular cystic lesions: T. Kurabayashi et al.
Type I
Type II
Type III
Type IV
Figure 2 Lesions were classified by extent into four types. Typical CT images are shown on the left; arrows point to the cystic lesions. Schematic drawings are on the right; the black area represents a cystic lesion. A. mylohyoid muscle; B. mandible; C. cervical vertebra
are inhomogeneous; we have seen two such cases which were excluded from this series due to an absence of clinical submandibular swelling. Lateral cervical cysts were also homogeneous but their individual density varied widely. Others have reported them as showing fluid density on CT 13 · 15 • The contents of lateral cervical cysts are reported to vary 32
Dentomaxillofac. Radiol., 1991, Vol. 20, February
from watery fluid to gelatinous, mucoid material In and this will explain the wide variation in the density. Extent
Lateral cervical cysts arise from the second branchial arch 15 and characteristically they displace the sternoc-
CT diagnosis of submandibular cystic lesions: T. Kurabayashi et al.
Figure 3 Lesions were classified into three types by shape. a. A lesion showing round or oval shape with smooth margin; b. a lesion with a concave margin; c. a multilocular lesion. Arrows point to the cystic lesions
Figure 4 A large variation in density was seen in lateral cervical cysts (arrows). a. A lateral cervical cyst showing fluid density (+ 10 HU) - the circle represents the region of interest (ROI) for measuring the density: b. a lateral cervical cyst whose density was similar to muscle (+57 HU)
Table II CT density of the lesions
Density Ranula
(HUj
10-19 20-29 30-39 40-49 50-59 60-69
6 9 5
Total
Table IV Shape of the lesions
Dermoid cyst
Lateral cervical cyst
3
I 4
2 2
I
o o o
o o o
0 I I
20
7
8
Smooth margin
Concave margin
Multilocular
Total 20
Ranula
3
12
5
Dermoid cyst
6
I
0
7
Lateral cervical cyst
8
0
0
8
17
13
5
35
Total
Table V Correlation between extent and shape of lesions
Extent of lesion
Table III Extent of the lesions
Type I
Type"
Type 11/
Type IV
Total
Ranula
0
6
4
10
20
Dermoid cyst
0
4
0
7
Lateral cervical cyst
8
0
3 0
0
8
Total
8
10
7
For definition of types of lesion see Materials and methods.
10
35
Type and shape of lesion
Type I
Ranula Unilocular Multilocular
0 0
Dermoid cyst Unilocular Multilocular
Type 11/ Type IV
Total
5 (2) I
4 (4) 0
6 (6) 4
15 (12) 5
0 0
4 0
3 (I) 0
0 0
Lateral cervical cyst Unilocular 8 Multilocular 0
0 0
0
0
8
0
0
0
Total
8
Type"
10 (2)
7 (5)
10 (6)
7 (I) 0
35 (13)
Numbers in parentheses are the lesions with concave margin.
Dentomaxillofac. Radial., 1991, Vol. 20, February 33
CT diagnosis of submandibular cystic lesions: T. Kurabayashi et al. leidomastoid muscle posterolaterally, the carotid and jugular vessels posteromedially and the submandibular gland anteriorly 13.15. Such displacement of the surrounding tissues was seen in all our cases so that these cysts can easily be differentiated from ranulas and dermoid cysts. Ten of the 20 ranulas were classified as type IV, unlike any of the dermoid or lateral cervical cysts. This pattern can therefore be taken as the characteristic CT appearance of ranulas. Type IV indicates that the lesion lies both above and below the mylohyoid muscle. Coit et al. 13 have also reported a similar CT appearance in two out of seven plunging ranulas. Ranulas arise in the sublingual space from obstruction of the duct of sublingual or minor salivary glands 1,2. As they enlarge, they extend easily into the submandibular space either around the posterior margin or through hiatuses in the mylohyoid muscle and so cause clinical swelling in this region. That only ranulas showed type IV appearance may be due to the fact that most are extravasation cysts 1-5 which easily flood into the surrounding connective tissues.
Shape of lesions Six out of seven dermoids and all of the lateral cervical cysts were unilocular and had smooth margins. In contrast, only three out of 20 ranulas had this shape and the others were multilocular or had partly concave margins. Plunging ranulas are clinically multilocular in nature 2 , 17 and one-quarter of those in our series had this appearance. The concave regions seen in the margins are due to depressions caused by anatomical structures adjacent to the lesion. Ranulas extending into the sublingual space were guitar shaped, due to pressure from the genioglossus, hyoglossus and mylohyoid muscles, while the concavity in the anterior part of the submandibular space was caused by the mylohyoid muscle or the submandibular lymph node. The contour of ranula appears to be readily affected by surrounding structures, probably due to the fact that most are pseudo-cysts 1.4 without epithelial lining.
Differential diagnosis On the basis of extent alone, it is not possible to differentiate lesions classified as type II or III as either ranulas or dermoid cysts. However, when these findings are combined with those for shape, they can be differentiated to some extent (Table V): type III lesions with a smooth margin can be diagnosed as dermoid cysts, and those with a concave margin as probably ranulas. The type II lesions with a multilocular or
34
Dentomaxillofac. Radiol., 1991, Vol. 20, February
concave margin can be confidently identified as ranulas, but a smooth margin does not help to differentiate ranulas from dermoid cysts, On the other hand, type I lesions can be diagnosed as lateral cervical cysts and type IV as ranulas. Although CT density was not so valuable for the differential diagnosis, ranulas and dermoid cysts can be excluded when it is similar to that of muscle.
References 1. Quick CA, Lowell SH. Ranula and the sublingual glands. Arch Otolaryngol1977 103: 397-400. 2. Catone GA, Merrill RG, Henry FA. Sublingual gland mucusescape phenomenon - treatment by excision of sublingual gland. J Oral Surg 1969; 27: 774-786. 3. Roediger WEW, Kay S. Pathogenesis and treatment of plunging ranulas. Surg Gynecol Obstet 1977; 144: 862-864. 4. Akker HP, Bays RA, Becker AE. Plunging or cervical ranula. J Maxillofac Surg 1978; 6: 286-293. 5. Meranus H, Kisis A, Serdin R. Extravasation cysts. Oral Surg Oral Med Oral Patho11968; 26: 427-433. 6. Galloway RH, Gross PO, Thompson SH, Patterson AL. Pathogenesis and treatment of ranula: report of three cases. J Maxillofac Surg 1989; 47: 299-302. 7. Ida M, Honda E. Age-dependent decrease in the computed tomographic numbers of parotid and submandibular salivary glands. Dentomaxillofac Radio11989; 18: 31-35. 8. Roediger WEW, Lloyd P, Lawson HH. Mucous extravasation theory as a cause of plunging ranulas. Br J Surg 1973; 60: 720722. 9. Meyer l. Dermoid cysts (dermoids) of the floor of the mouth. Oral Surg Oral Med Oral Pathol 1955; 8: 1149-1164. to. Howell CJT. The sublingual dermoid cyst. Oral Surg Oral Med Oral Pathol 1985; 59: 578-580. 11. Seward GR. Dermoid cysts of the floor of the mouth. Br J Oral Surg 1965; 3: 36-47. 12. Charnoff SK, Carter BL. Plunging ranula: CT diagnosis. Radiology 1986; 158: 467-468. 13. Coit WE, Harnsberger HR, Osborn AG, Smoker WRK, Stevens MH, Lufkin RB. Ranulas and their mimics: CT evaluation. Radiology 1987; 163: 211-216. 14. Hunter TB, Papranus SH, Chernin MM, Coulthard SW. Dermoid cyst of the floor of the mouth: CT appearance. AJR 1983; 141: 1239-1240. 15. Harnsberger HR, Mancuso AA, Muraki AS et al. Branchial cleft anomalies and their mimics: computed tomographic evaluation. Radiology 1984; 152: 739-748. 16. Shafer WG, Hine MK, Levy BM. A Textbook of Oral Pathology. Philadelphia: W.B. Saunders, 1974; 72-74. 17. Rene AK, Schwarts A, Friedman E. The plunging ranula. J Oral Surg 1975; 33: 537-541. Address: Dr T. Kurabayashi, Tokyo Medical and Dental University, Department of Dental Radiology and Radiation Research, Faculty of Dentistry, Yushima 1-5-45, Bunkyo-ku. Tokyo 113, Japan.
