Ultrasonic diagnosis of masseteric hypertrophy M.H. Morse and E.F. Brown Department of Radiodiagnosis, Bristol Royal Infirmary, Bristol, UK
Received 21 June 1989 and in final form 10 October 1989 Masseteric hypertrophy may present a diagnostic dilemma, its confirmation frequently being by exclusion of other conditions. The literature relating to this syndrome is reviewed. A study to confirm the suitability of ultrasound in diagnosis, and to establish a normal range, is described. Sixty-two masseter muscles were measured using a standardized technique and the derived normal range for transverse dimension was 8.5-13.5 mm. Three instances of clinically diagnosed masseteric hypertrophy were examined; in each case measured transverse masseteric dimension was significantly greater than the normal range. Direct ultrasonic measurement of masseteric bulk should replace computed tomography as the definitive investigation in suspected cases. Keywords: Masticatory muscles; ultrasonic diagnosis; hypertrophy
Masseteric hypertrophy usually presents as a relatively firm, painless, pre-auricular swelling, but may cause considerable diagnostic difficulty. Maxillofacial, plastic or ENT surgeons are usually aware of the syndrome, but others to whom the patient may present are frequently not familiar with the appearances, and may investigate the patient inappropriately. There is, in either case, a need to be able to confirm the diagnosis other than by exclusion. Differential diagnoses as diverse as parotitis, parotid tumour, lipoma, benign or malignant muscle tumours, vascular tumours, benign or malignant mandibular tumours, fibrodysplasia ossificans and mumps have all been attributed to this condition 1. Plain radiographs and sialography may be helpful, but the only specific investigation at present available is computed tomography, often combined with sialography. We describe a diagnostic technique using ultrasound, the establishment of a normal range by its application to a control population and its use on patients with clinical masseteric hypertrophy.
Method Measurements were performed on volunteers who were asymptomatic and whose age range reflected that found in patients with masseteric hypertrophy. Subjects were placed in the lateral position, head supported on a pillow, with facial muscles relaxed and teeth just apart (corresponding approximately to the physiological mandibular rest position). A 5 MHz linear array transducer (Acuson, Stevenage, UK), with stand-off device (Kitecko, 3M, Loughborough, UK), was then positioned at the level of, and parallel to, the occlusal plane, overlying the bulk of the masseter muscle. Measurements were taken of its maximum transverse dimension (Figure 1) which usually lay just anterior to the ascending ramus of the mandible, directly from the screen. Without repositioning the transducer, the measurement was repeated with the subject clenching 18 Dentomaxillofac. Radiol., 1990, Vol. 19, February
the teeth together. The contralateral side was then measured, and the results expressed to the nearest 0.5 mm. In preliminary experiments, this protocol was found to have a high level of intra-observer (M.H.M.) reproducibility.
Results Initial measurements obtained on subjects with dentures suggested that, in such cases, masseteric bulk was often considerably reduced; they were therefore withdrawn from the study. Sixty-two measurements were recorded on 31 subjects with full dentitions, 15 males and 16 females. Mean age was 30.3 years (range 20-50 years), mean height 1.75m (range 1.52-2.00m), and mean weight 69.5 kg (range 47-111 kg). In the relaxed position, mean maximum transverse dimension was 1O.8mm (range 8.5-15.0mm, so 1.24mm). In the clenched position, it was 13.4mm (range 11.017.0mm, so 1.47mm). The derived normal ranges (mean ±2 so, expressed to the nearest 0.5 mm) were therefore: Relaxed position
8.5-13.5mm
Clenched position
10.5-16.5 mm
Discussion There are commonly no obvious predisposing factors in cases of benign masseteric hypertrophy, but nocturnal bruxism, temporomandibular joint disturbance, malocclusion or missing dentition and psychological disturbance have all been implicated-:". Riefkohl et al.' reviewed 108 published cases, 93% of whom were between the ages of 10 and 40 years with an average age of 30. Approximately half the cases were bilateral, some symmetrical, others asymmetrical. There was a slight male preponderance. Ninety per cent of those cases with mandibular radiographs showed either the
© 1990 IADMFR 02SG-832 x 90/010018
Ultrasound in masseteric hypertrophy: M.H. Morse and E.F. Brown
-'--
r--~_m
_
r ~
ant med
t b Figure 1 (a) Ultrasound image of normal masseter and anterior margin of parotid gland. +, Measurement end points. (b) Line tracing of a, showing masseter (m), parotid gland (p) and acoustic shadowing caused by ascending ramus (r). Orientation as described in text. ant, anterior; med, medial
Figure 2 Ultrasound image of hypertrophied masseter, orientation as for Figure 1
bony spurs or flaring of the angle of the mandible which are partly responsible for the 'quadrangular' facies seen in such patients". The diagnosis in the majority of this series was based on clinical grounds, but in many cases was not apparent until operation 1. 8. The sialographic findings of a normal parotid intraglandular ductal system with a laterally displaced main duct are classical", but this appearance is not specific for masseteric hypertrophy. Black and Schloss'? used computed tomography in two cases and described it as a most valuable diagnostic tool. Similarly, Braun et al. I I considered it the ideal method. Their three cases were, however, unilateral, allowing direct comparison with a presumed normal contralateral muscle; all had conventional sialography, and one needed sialography during cr to confirm the diagnosis. There is obviously
a need for a more convenient diagnostic procedure and hence our interest in ultrasound. We have found two reports of the use of diagnostic ultrasound in masseteric hypertrophys-!", In both cases, however, it was used as a secondary diagnostic modality to cr, and in neither instance was any attempt made to establish a specific technique or normal range. In the case described by Black and Schloss 10, the ultrasonic findings were misinterpreted, being thought compatible with the provisional preoperative diagnosis of parotid tumour. The report by Tauber et al. s suggests that the overall shape, rather than the size of the masseter, is diagnostic, a subjective view not borne out by our experience in this series. The plane of the ultasound beam in the described position is at approximately 20° to the long axis of the muscle fibres, but this has no bearing on a purely transverse measurement. The great advantage of this position lies in its rapid and easy determination in all patients. We initially used a linear array transducer with a stand-off device, but have found reproducible results with a variety of sector scanners. Provided that the soft tissues are not unduly compressed, the standoff may also be dispensed with, in which case the use of a relatively short-focus transducer will optimize the images. At no time did we find difficulty in identifying the boundaries of the masseter: the echo pattern of muscle and parotid gland is sufficiently dissimilar to make distinction easy, in contrast to computed tomography, where this may not always be the case 11. We have not attempted to derive separate normal ranges for male and female subjects because, in our relatively small sample, there was no significant difference in measurement between the two populations (P>0.1). This finding is supported by the work of Weijs and Hillen 12. who have shown that there is a complex relationship between the cross-sectional area of muscles of mastication and various parameters of craniofacial morphology, but no simple correlation with overall skull size. Masseteric transverse dimension in the clenched Dentomaxillofac. Radiol., 1990, Vol. 19, February
19
Ultrasound in masseteric hypertrophy: M.H. Morse and E.F. Brown teeth position was measured in an attempt to judge whether the degree of increase in that dimension when compared with the relaxed state would be a positive discriminant for hypertrophy. Our findings suggest that transverse dimension normally increases by 20-25% on clenching; we have since seen patients with masseteric hypertrophy in whom there was a similar order of increase on clenching, despite very significant enlargement of the masseters in both relaxed and clenched positions compared with the normal range established in this study. We suggest, therefore, that measurement in the clenched teeth position is not of predictive value. The parotid glands should be examined at the same time as the masseters, even if masseteric hypertrophy has already been proven, in view of the possibility of concurrent pathology. The relatively variable size and position of the parotids makes it unrealistic to ascribe normal dimensions without a full, time-consuming survey of each individual gland; however, the ultrasonic appearances are such that a rapid survey will exclude focal lesions, significant vascular displacement or marked generalized enlargement. We have examined two patients with clinically suspected masseteric hypertrophy using this technique, both young adult males. One patient had relatively symmetrical hypertrophy, with resting transverse masseteric dimension of 19mm and 18mm, the other had unilateral hypertrophy, with one masseter measuring 17mm (Figure 2), the other 13 mm. Each abnormal measurement was therefore significantly outside the normal range (P < 0.05). In neither case was there ultrasonic evidence of other abnormality. We conclude that, in cases of masseteric hypertrophy, a panoramic radiograph or anteroposterior projection of the mandible, together with ultrasonic examination of the masseter muscles and parotid glands, including direct measurement of the transverse dimension of the relaxed masseter, will be diagnostic
20 Dentomaxillofac. Radiol., 1990, Vol. 19, February
and avoid the need for sialography and computed tomography.
Acknowledgements We are grateful to Mr J.W. Ross and Mr R.K. Roddie for referring patients for investigation.
References 1. Riefkohl R, Georgiade GS, Georgiade NG. Masseter muscle hypertrophy. Ann Plast Surg 1984; 12: 528-32. 2. Masters F, Georgiade N, Pickrell K. The surgical treatment of benign masseteric hypertrophy. Plast Reconstr Surg 1955; 15: 215-21. 3. Hersch JG. Hypertrophy of the masseter muscle. Arch Otolaryngol Head Neck Surg 1946; 43: 593-6. 4. Tempest MN. Simple unilateral hypertrophy of the masseter muscle. Br J Plast Surg 1951; 4: 136-8. 5. Lash H. Benign masseteric hypertrophy. Surg C/in North Am 1963; 43: 1357-60. 6. Guggenheim P, Cohen L. The nature of masseteric hypertrophy. Arch Otolaryngol Head Neck Surg 1961; 73: 15-28. 7. Waldhart E, Lynch JB. Benign hypertrophy of the masseter muscles and mandibular angles. Arch Surg 1971; 102: 115-8. 8. Tauber T, Starin sky R, Varsano D. Ultrasonic and computed tomographic diagnosis of benign masseteric hypertrophy. Pediatr RadioI1986; 16: 238-9. 9. Dee PM. Benign hypertrophy of the masseters; a report of radiological features in two cases. Clin RadioI1964; 15: 347-9. 10. Black MJ, Schloss MD. Masseteric muscle hypertrophy. J Otolaryngol1985; 14: 203-5. 11. Braun IF, Torres WE, Landman JA, Davis PC, Hoffman JC JT. Computed tomography of benign masseteric hypertrophy. J Comput Assist Tomogr 1985; 9: 167-70. 12. Weijs WA, Hillen B. Correlations between the cross sectional area of the jaw muscles and craniofacial size and shape. Am J Phys Anthropol 1986; 70: 423-31. Address: Dr M.H. Morse, Department of Radiodiagnosis, Frenchay Hospital, Bristol BS16 lLE, UK.
Received 21 June 1989 and in final form 10 October 1989 Masseteric hypertrophy may present a diagnostic dilemma, its confirmation frequently being by exclusion of other conditions. The literature relating to this syndrome is reviewed. A study to confirm the suitability of ultrasound in diagnosis, and to establish a normal range, is described. Sixty-two masseter muscles were measured using a standardized technique and the derived normal range for transverse dimension was 8.5-13.5 mm. Three instances of clinically diagnosed masseteric hypertrophy were examined; in each case measured transverse masseteric dimension was significantly greater than the normal range. Direct ultrasonic measurement of masseteric bulk should replace computed tomography as the definitive investigation in suspected cases. Keywords: Masticatory muscles; ultrasonic diagnosis; hypertrophy
Masseteric hypertrophy usually presents as a relatively firm, painless, pre-auricular swelling, but may cause considerable diagnostic difficulty. Maxillofacial, plastic or ENT surgeons are usually aware of the syndrome, but others to whom the patient may present are frequently not familiar with the appearances, and may investigate the patient inappropriately. There is, in either case, a need to be able to confirm the diagnosis other than by exclusion. Differential diagnoses as diverse as parotitis, parotid tumour, lipoma, benign or malignant muscle tumours, vascular tumours, benign or malignant mandibular tumours, fibrodysplasia ossificans and mumps have all been attributed to this condition 1. Plain radiographs and sialography may be helpful, but the only specific investigation at present available is computed tomography, often combined with sialography. We describe a diagnostic technique using ultrasound, the establishment of a normal range by its application to a control population and its use on patients with clinical masseteric hypertrophy.
Method Measurements were performed on volunteers who were asymptomatic and whose age range reflected that found in patients with masseteric hypertrophy. Subjects were placed in the lateral position, head supported on a pillow, with facial muscles relaxed and teeth just apart (corresponding approximately to the physiological mandibular rest position). A 5 MHz linear array transducer (Acuson, Stevenage, UK), with stand-off device (Kitecko, 3M, Loughborough, UK), was then positioned at the level of, and parallel to, the occlusal plane, overlying the bulk of the masseter muscle. Measurements were taken of its maximum transverse dimension (Figure 1) which usually lay just anterior to the ascending ramus of the mandible, directly from the screen. Without repositioning the transducer, the measurement was repeated with the subject clenching 18 Dentomaxillofac. Radiol., 1990, Vol. 19, February
the teeth together. The contralateral side was then measured, and the results expressed to the nearest 0.5 mm. In preliminary experiments, this protocol was found to have a high level of intra-observer (M.H.M.) reproducibility.
Results Initial measurements obtained on subjects with dentures suggested that, in such cases, masseteric bulk was often considerably reduced; they were therefore withdrawn from the study. Sixty-two measurements were recorded on 31 subjects with full dentitions, 15 males and 16 females. Mean age was 30.3 years (range 20-50 years), mean height 1.75m (range 1.52-2.00m), and mean weight 69.5 kg (range 47-111 kg). In the relaxed position, mean maximum transverse dimension was 1O.8mm (range 8.5-15.0mm, so 1.24mm). In the clenched position, it was 13.4mm (range 11.017.0mm, so 1.47mm). The derived normal ranges (mean ±2 so, expressed to the nearest 0.5 mm) were therefore: Relaxed position
8.5-13.5mm
Clenched position
10.5-16.5 mm
Discussion There are commonly no obvious predisposing factors in cases of benign masseteric hypertrophy, but nocturnal bruxism, temporomandibular joint disturbance, malocclusion or missing dentition and psychological disturbance have all been implicated-:". Riefkohl et al.' reviewed 108 published cases, 93% of whom were between the ages of 10 and 40 years with an average age of 30. Approximately half the cases were bilateral, some symmetrical, others asymmetrical. There was a slight male preponderance. Ninety per cent of those cases with mandibular radiographs showed either the
© 1990 IADMFR 02SG-832 x 90/010018
Ultrasound in masseteric hypertrophy: M.H. Morse and E.F. Brown
-'--
r--~_m
_
r ~
ant med
t b Figure 1 (a) Ultrasound image of normal masseter and anterior margin of parotid gland. +, Measurement end points. (b) Line tracing of a, showing masseter (m), parotid gland (p) and acoustic shadowing caused by ascending ramus (r). Orientation as described in text. ant, anterior; med, medial
Figure 2 Ultrasound image of hypertrophied masseter, orientation as for Figure 1
bony spurs or flaring of the angle of the mandible which are partly responsible for the 'quadrangular' facies seen in such patients". The diagnosis in the majority of this series was based on clinical grounds, but in many cases was not apparent until operation 1. 8. The sialographic findings of a normal parotid intraglandular ductal system with a laterally displaced main duct are classical", but this appearance is not specific for masseteric hypertrophy. Black and Schloss'? used computed tomography in two cases and described it as a most valuable diagnostic tool. Similarly, Braun et al. I I considered it the ideal method. Their three cases were, however, unilateral, allowing direct comparison with a presumed normal contralateral muscle; all had conventional sialography, and one needed sialography during cr to confirm the diagnosis. There is obviously
a need for a more convenient diagnostic procedure and hence our interest in ultrasound. We have found two reports of the use of diagnostic ultrasound in masseteric hypertrophys-!", In both cases, however, it was used as a secondary diagnostic modality to cr, and in neither instance was any attempt made to establish a specific technique or normal range. In the case described by Black and Schloss 10, the ultrasonic findings were misinterpreted, being thought compatible with the provisional preoperative diagnosis of parotid tumour. The report by Tauber et al. s suggests that the overall shape, rather than the size of the masseter, is diagnostic, a subjective view not borne out by our experience in this series. The plane of the ultasound beam in the described position is at approximately 20° to the long axis of the muscle fibres, but this has no bearing on a purely transverse measurement. The great advantage of this position lies in its rapid and easy determination in all patients. We initially used a linear array transducer with a stand-off device, but have found reproducible results with a variety of sector scanners. Provided that the soft tissues are not unduly compressed, the standoff may also be dispensed with, in which case the use of a relatively short-focus transducer will optimize the images. At no time did we find difficulty in identifying the boundaries of the masseter: the echo pattern of muscle and parotid gland is sufficiently dissimilar to make distinction easy, in contrast to computed tomography, where this may not always be the case 11. We have not attempted to derive separate normal ranges for male and female subjects because, in our relatively small sample, there was no significant difference in measurement between the two populations (P>0.1). This finding is supported by the work of Weijs and Hillen 12. who have shown that there is a complex relationship between the cross-sectional area of muscles of mastication and various parameters of craniofacial morphology, but no simple correlation with overall skull size. Masseteric transverse dimension in the clenched Dentomaxillofac. Radiol., 1990, Vol. 19, February
19
Ultrasound in masseteric hypertrophy: M.H. Morse and E.F. Brown teeth position was measured in an attempt to judge whether the degree of increase in that dimension when compared with the relaxed state would be a positive discriminant for hypertrophy. Our findings suggest that transverse dimension normally increases by 20-25% on clenching; we have since seen patients with masseteric hypertrophy in whom there was a similar order of increase on clenching, despite very significant enlargement of the masseters in both relaxed and clenched positions compared with the normal range established in this study. We suggest, therefore, that measurement in the clenched teeth position is not of predictive value. The parotid glands should be examined at the same time as the masseters, even if masseteric hypertrophy has already been proven, in view of the possibility of concurrent pathology. The relatively variable size and position of the parotids makes it unrealistic to ascribe normal dimensions without a full, time-consuming survey of each individual gland; however, the ultrasonic appearances are such that a rapid survey will exclude focal lesions, significant vascular displacement or marked generalized enlargement. We have examined two patients with clinically suspected masseteric hypertrophy using this technique, both young adult males. One patient had relatively symmetrical hypertrophy, with resting transverse masseteric dimension of 19mm and 18mm, the other had unilateral hypertrophy, with one masseter measuring 17mm (Figure 2), the other 13 mm. Each abnormal measurement was therefore significantly outside the normal range (P < 0.05). In neither case was there ultrasonic evidence of other abnormality. We conclude that, in cases of masseteric hypertrophy, a panoramic radiograph or anteroposterior projection of the mandible, together with ultrasonic examination of the masseter muscles and parotid glands, including direct measurement of the transverse dimension of the relaxed masseter, will be diagnostic
20 Dentomaxillofac. Radiol., 1990, Vol. 19, February
and avoid the need for sialography and computed tomography.
Acknowledgements We are grateful to Mr J.W. Ross and Mr R.K. Roddie for referring patients for investigation.
References 1. Riefkohl R, Georgiade GS, Georgiade NG. Masseter muscle hypertrophy. Ann Plast Surg 1984; 12: 528-32. 2. Masters F, Georgiade N, Pickrell K. The surgical treatment of benign masseteric hypertrophy. Plast Reconstr Surg 1955; 15: 215-21. 3. Hersch JG. Hypertrophy of the masseter muscle. Arch Otolaryngol Head Neck Surg 1946; 43: 593-6. 4. Tempest MN. Simple unilateral hypertrophy of the masseter muscle. Br J Plast Surg 1951; 4: 136-8. 5. Lash H. Benign masseteric hypertrophy. Surg C/in North Am 1963; 43: 1357-60. 6. Guggenheim P, Cohen L. The nature of masseteric hypertrophy. Arch Otolaryngol Head Neck Surg 1961; 73: 15-28. 7. Waldhart E, Lynch JB. Benign hypertrophy of the masseter muscles and mandibular angles. Arch Surg 1971; 102: 115-8. 8. Tauber T, Starin sky R, Varsano D. Ultrasonic and computed tomographic diagnosis of benign masseteric hypertrophy. Pediatr RadioI1986; 16: 238-9. 9. Dee PM. Benign hypertrophy of the masseters; a report of radiological features in two cases. Clin RadioI1964; 15: 347-9. 10. Black MJ, Schloss MD. Masseteric muscle hypertrophy. J Otolaryngol1985; 14: 203-5. 11. Braun IF, Torres WE, Landman JA, Davis PC, Hoffman JC JT. Computed tomography of benign masseteric hypertrophy. J Comput Assist Tomogr 1985; 9: 167-70. 12. Weijs WA, Hillen B. Correlations between the cross sectional area of the jaw muscles and craniofacial size and shape. Am J Phys Anthropol 1986; 70: 423-31. Address: Dr M.H. Morse, Department of Radiodiagnosis, Frenchay Hospital, Bristol BS16 lLE, UK.
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