Ultrasonography Advantages and Disadvantages

ULTRASONOGRAPHY

Ultrasonography is a sound based diagnostic imaging technique used for visualising subcutaneous body structures including muscles joints vessels and internal organs for possible pathology and lesions.

Sonography was introduced in the Medical field in early 1950’s with steady development. The requirement of Ultrasound has gained importance in medical field and slowly its use in dentistry is also advancing. In Ultrasonography high frequency sound waves are transmitted in to the body by a transducer and the reflected waves are detected and displayed on a monitor. Sound reflection occurs between materials with different acoustic properties. The acoustic impedance of a medium is the product of its density and the propagation velocity in the medium.

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The transducers are intended to produce longitudinal waves therefore only those waves can pass through tissues get reflected, Audio frequency of a sound wave is 20 KHz any frequency above this is known as ultrasound. Medical Ultrasound uses the frequency of 1-15 MHz. The transducer contains quartz crystals and works on a principle called as piezoelectric effect. Piezoelectric effect is when a force is applied perpendicular to the faces of a quartz crystal an electric charge will result. This charge can be de­tected and amplified, producing a useful electric signal. Conversely, if an electric sig­nal is applied to the crystal, expansion or con­traction of the crystal will take place depend­ing on the polarity of the signal. Oscillating signals cause the crystal to vi­brate, resulting in propagation of sound waves into the medium with which the crystal is in contact.⁵²

Advantages of this imaging technique include –

• Non invasive
• Non ionizing radiation is used
• Simple
• Real time imaging
• Portable machine
• Can repeat and easy to store
• Less artifacts

Disadvantages include –

• Operator and equipment dependant
• Hard tissue cannot be imaged
• Deep structures cannot be visualized

Application of Ultrasonography in dentistry:

Ultrasonography has been used as non-invasive technique for the imaging of relatively deep areas. Recently, however high frequency USG has been developed that can provide detail investigation of more superficial regions.^{53, 54} USG has extensive range of use in dentistry such as to detect cyst and tumors of orofacial region, lympadenitis, space infections, temporomandibular joint (TMJ) disorders and mid face fractures.

USG can detect of fractures of the maxillofacial region i.e. nasal bone fractures, orbital rim fractures, maxillary fractures, mandibular fractures, zygomatic arch fractures as well as reduction & healing of fractures.

Ultrasound is used to detect parotid lesions, where solid and cystic lesions are reliably differentiated and diffuse enlargement of the parotid gland (or) focal disease is readily shown by ultrasound. Sonographically, benign lesions usually appear well defined, homogeneous and hypoechoic, while malignant lesions tend to be ill defined and hypoechoic with heterogeneous internal architecture and enlarged cervical lymph node may be visible and reactive intra parotid lymph nodes may also be readily assessed.^{55, 56, 57}

USG can also be used during FNAC. This technique offers the ability to sample non palpable diseases, gives access to different regions of the lesion and approaches the lesion from different angles. During biopsy of parotid gland there is chance of injuring the facial nerve (or) seeding neoplastic cells, under ultrasound guidance these can be avoided.⁵⁶

The value of USG is well recognized in inflammatory soft tissue conditions of the head and neck region and superficial tissue disorders of the maxillofacial region. Ultra sound can provide the content of the lesion before any surgical procedure; both solid and cystic contents could be identified in ultrasound. The mixed lesions should be considered neoplastic and should be biopsied before surgical procedure.USG helps in detecting the extend of space infections in oral and maxillofacial region.

Ultrasound is also an precise modality for measuring the thickness of muscles, data regarding thickness may provide information useful in diagnosis and treatment especially in follow up examination in cases of temporomandibular joint disorders (TMD).⁵⁸ USG is indiacted in TMD to evaluate the osseous contours of joints and joint space, joint effusion, detection of disc position and dynamic evaluation and inflammatory disorders like Rheumatoid arthritis, psoriatic arthritis etc.

Ultrasound can also be used for detecting sialoliths in parotid, submandibular and sublingual salivary glands, which appear as echo-dense spots with a characteristic acoustic shadow.⁵⁹ In Ultrasound, color Doppler sonography has been developed to identify vasculatures and to enable evaluation of the blood flow, velocity and vessel resistance together with surrounding Morphology. It can be used for detecting the course of the facial artery and for detecting hemangioma. So the use of ultrasound is unlimited, so proper application of this Imaging can be of use in detecting various normal & pathological lesions in the maxillofacial region.

Literature search

Manjunath K et al (2011) evaluated oral submucous fibrosis (OSMF) by clinical and histopathological examination, and compared the results with those from ultrasonographic technique.30 clinically diagnosed OSMF patients were subjected to both ultrasonographic and histopathological evaluation before treatment. Later, only ultrasonographical examination using 9-5 MHz transducer was done during 4^thand 8^thweek of treatment. Intralesional injections of a combination of dexamethasone sodium phosphate 4 mg/ml and hyaluronidase 1500 IU twice a week for 8 weeks were given. At each visit, following topical application of lignocaine 2%, 1500 IU of hyaluronidase was dissolved in 2.0 ml of dexamethasone sodium phosphate in a 2 ml disposable syringe and the drugs were injected at multiple sites submucosally by means of a gauge 24 needle, taking care that not more than 0.2 ml solution was injected per site. Prognosis of the lesion for the treatment was evaluated. Peak systolic velocity (PSV) of blood in the lesional area was statistically analyzed. 10 normal individuals without any mucosal lesions were considered as the control group.In normal individuals, ultrasonography delineated normal mucosa with uniform fine mottled appearance with interspersed hypoechoic areas. Colour Doppler and spectral Doppler depicted uniform distribution of blood vessels and normal peak systolic velocity of blood respectively. All OSMF patients were diagnosed upon clinical and histopathological examination. Clinical examination revealed 14 individuals with unilateral palpable fibrotic bands and 16 individuals with bilateral fibrotic bands whereas, ultrasonographic evaluation revealed 6 individuals with unilateral fibrotic bands and 24 individuals were with bilateral fibrotic bands, which was statistically significant. Ultrasonography demonstrated number, length and thickness of the fibrotic bands. Color Doppler and spectral Doppler showed decreased vascularity and PSV in lesional area. Prognosis evaluation revealed 25 cases of good prognosis and 5 cases were showed poor prognosis. Wilcoxon Signed Ranks Test revealed no significant difference of PSV was seen in poor prognosis patients.The study concluded that Ultrasonography could be a better diagnostic tool compared to clinical and histopathological examination.²

Krithika C et al (2013) assessed the sonographic features of the buccal mucosa in patients with oral submucous fibrosis (OSF).Three groups (controls with areca-related habits, controls without areca-related habits and clinically diagnosed OSF cases), each comprising 30 subjects, were included in the study. After a thorough clinical examination, transcutaneous B-mode ultrasonography was performed with a multifrequency linear transducer (5-10 MHz) for anterior and posterior buccal mucosa bilaterally. Both clinical and ultrasound findings were recorded by three independent observers. One-way analysis of variance and Tukey’s honestly significant difference post-hoc tests were used for statistical comparisons between groups and Pearson χ (2) tests to compare the proportions. Kappa statistics was used to determine the interobserver agreement. The submucosa that appeared hypoechoic in the control groups had significantly increased echogenicity in the case group (hypo- to isoechoic in 46.7% and isoechoic in 53.3%). The differentiation between the submucosa and the muscle layer appeared distinct in the control groups while it was not clear in the case group (indistinct in 50% and completely lost in 50%). The number of sites found positive on the ultrasound was significantly greater than the number of clinically positive sites. There was a very good inter observer consistency in clinical and ultrasound findings. Ultrasonography of the buccal mucosa demonstrated increased submucosal echogenicity and reduced echo differentiation between submucosa and muscle layer in OSF cases. Hence, it can be used as a non-invasive imaging modality to assess the disease extent and severity across the entire buccal mucosa to supplement clinical evaluation.⁷

P Rangaiah (2010) performed a hospital based cross sectional study to measure the thickness of submucosa with the application of high frequency ultrasonography (USG) in cases and controls and to correlate clinical and histological stages of the disease with the USG measurements. Study consisted of 20 subjects who were clinically and histopathologically proven of OSMF and 20 controls who were selected by matching the age & body mass index to OSMF patients. Transcutaneous imaging of Buccal and labial submucosa was done using a high frequency (3-12 MHz) USG. The values were correlated with the habit and clinical and histological staging of the disease. Result The mean submucosal thickness of ABM for cases was0.209 ± 0.072 cms and for controls was 0.056 ± 0.011 cms, PBM for cases was 0.218 ± 0.080 and for controls was 0.057 ± 0.010 cms, ULM for cases was 0.149 ± 0.051 cms and for controls was 0.055 ± 0.015 cms, and for LLM for cases was 0.162 ± 0.052 cms and for the controls was 0.060 ± 0.017 cms. The study group had a increased submucosal thickness when compared to control group in all the measured sites. A significant positive association was obtained in relation of submucosal thickness with frequency of chewing habits. An insignificant correlation was obtained with respect to submucosal thickness with duration of habit and duration of quid keeping. An incompatibility was noted when comparison of clinical and histological staging was done with USG measurements, which could be attributed to smaller sample size, unequal number of subjects in each staging of OSMF. But many cases showed definite increase in submucosal thickness as the disease progressed from early to advanced stage. Echogenecity pattern of submucosa showed areas of irregular hyperechoic (increased) linear streaks due to fibrotic deposits in cases. In the contrary the submucosa of controls appeared as a band of hypoechoic zone. Conclusion of the present preliminary study was able to establish the normal values of submucosal thickness ultrasonographically for a small group of South Indian population. The study showed a significant increase in submucosal thickness in OSMF patients which was measured ultrasonographically.⁶⁰

Devathambi JR (2013) evaluated the efficacy of ultrasonography (USG) as a non-invasive tool in assessing the severity of OSMF and also to assess the relationship between OSMF and hypertrophy of the masseter muscle. The submucosal thickness in buccal mucosa and masseteric muscle hypertrophy were measured using ultrasound (10-15 MHz) in 60 patients comprising 30 OSMF patients and 30 controls. Results were analyzed by one way analysis of variance, Chi-square test and t- test. The range of the normal submucosal thickness in the study was between 0.045 and 0.056 cm.the submucosal thickness in OSMF patients ranged between 0.090cm to 0.258.As the stages of OSMF advanced there was an increase in submucosal thickness of the buccal mucosa as well as masseter muscle thickness in both relaxed and contracted state in the study group when compared with controls (P< 0.005).⁶¹

P Kant (2014) evaluated the efficacy of ultrasonography (USG) as a non-invasive tool in assessing the severity of OSMF and also to assess the relationship between OSMF and hypertrophy of the masseter muscle. The submucosal thickness in buccal mucosa and masseteric muscle hypertrophy were measured using ultrasound (10-15 MHz) in 60 patients comprising 30 OSMF patients and 30 controls. Results were analyzed by one way analysis of variance, Chi-square test and t-test. As the stages of OSMF advanced there was an increase in submucosal thickness of the buccal mucosa as well as masseter muscle thickness in both relaxed and contracted state in the study group when compared with controls (p< 0.005).USG is an effective non-invasive zero radiation tool for assessing the progression of OSMF.⁶²

Kamala KA et al (2010) investigated thickness of masseter muscle at rest and at maximum clenching position by ultrasonography with masseter muscle hypertrophy in OSMF patient and control group, and also to establish the normal value of masseter muscle thickness ultrasonographically and to prove that ultrasonography is reliable diagnostic technique for the evaluation of masseter muscle hypertrophy in oral submucous fibrosis patient. Ultrasonographic (3-12 MHz) measurement of masseter muscle thickness was performed in 40 subjects including 20 OSMF patients and 20 controls. Study group showed higher thickness both on right and left buccal mucosa when compared to controls. The thickness of masseter muscle was more in contracted stage than relaxed stage which was significant.⁶³

J Jackowski et al (1999) compared the ultrasonographic appearances of the oral mucosa in health with patients with systemic sclerosis (SSc).An innovative 20 MHz US scanner was used to examine the lips, cheeks and oral vestibule of ten healthy persons and ten patients with SSc. The clinical, ultrasonographic and histopathological features of one patient with a fibro-epithelial polyp of the buccal mucosa are reported in detail. Two patients with SSc displayed increased echogenicity due to fibrotic deposits. A similar echo pattern was seen in the case of the histopathologically verified fibro-epithelial polyp of the buccal mucosa. The study concluded that 20 MHz sonography may be suitable as a non-invasive tool for evaluation of fibrosis of the oral mucosa.⁶⁴

Praveen Kumar Pandey et al (2011) The purpose of the study was to establish the role of ultrasonography in determining the involvement of specific fascial spaces in maxillofacial region and the stage of infection, in indicating the appropriate time for surgical intervention and to compare clinical and ultrasonographic findings.

Material and Methods

Twenty five patients with fascial space infection in maxillofacial region were subjected to ultrasonographic examination following a detailed clinical and radiological examination. Ultrasonography guided needle aspiration was performed. Based on the findings, patients diagnosed with abscess were subjected to incision and drainage and those with cellulitis were subjected to medical line of treatment.

Results

More than one fascial space was involved in all patients. On clinical examination 64 spaces were involved, of them 34 spaces had abscess formation and 30 spaces were in the stage of cellulitis. On ultrasonography examination, 28 spaces were reported to have abscess formation and 36 spaces were diagnosed to be in the stage of cellulitis. On comparative analysis of both clinical and ultrasonographic findings, ultrasonography was found to be sensitive in 65% of the cases and having specificity of 80%. It was registered statistically significant (P < 0.001) agreement between these two methods of assessment (kappa index = 0.814).

Conclusions

Ultrasonography is a quick, widely available, relatively inexpensive, and painless procedure and can be repeated as often as necessary without risk to the patient. Thus ultrasonography is a valuable diagnostic aid to the oral and maxillofacial surgeon for early and accurate diagnosis of fascial space infection, their appropriate treatment and to limit their further spread.

Keywords:ultrasonography, maxillofacial surgery, abscess, cellulitis, differential diagnosis.

The purpose of the study was to establish the role of ultrasonography in determining the involvement of specific facial spaces in maxillofacial region and the stage of infection, in indicating the appropriate time for surgical intervention and to compare clinical and ultrasonographic findings. Twenty five patients with fascial space infection in maxillofacial region were subjected to ultrasonographic examination following a detailed clinical and radiological examination. Ultrasonography guided needle aspiration was performed. Based on the findings, patients diagnosed with abscess were subjected to incision and drainage and those with cellulitis were subjected to medical line of treatment. More than one fascial space was involved in all patients. On clinical examination 64 spaces were involved, of them 34 spaces had abscess formation and 30 spaces were in the stage of cellulitis. On ultrasonography examination, 28 spaces were reported to have abscess formation and 36 spaces were diagnosed to be in the stage of cellulitis. On comparative analysis of both clinical and ultrasonographic findings, ultrasonography was found to be sensitive in 65% of the cases and having specificity of 80%. It was registered statistically significant (P < 0.001) agreement between these two methods of assessment (kappa index = 0.814).⁶⁵

Mohit sharma et al (2014) detected the role of ultrasonography as an adjunctive diagnostic aid for fascial space infections of odontogenic origin as well as an aid in appropriate treatment planning and management of fascial space infections of odontogenic origin. The study group comprised of 30 patients of either genders, irrespective of age and presented with unilateral fascial space infection of odontogenic origin. After the clinical and radiographic examinations, patients underwent USG evaluation. USG-guided intraoperative aspiration was done to confirm the diagnosis. All the findings were tabulated and subjected to statistical analysis.USG was as accurate as USG-guided intraoral aspiration (Gold standard) in diagnosing fascial space infections of odontogenic origin with sensitivity and specificity of 100%. In cases of abscess USG showed a well-defined homogenous anechoic pattern, cellulitis cases showed an ill-defined heterogeneous hyperechoic pattern while edema showed an ill-defined isoechoic pattern.The different stages of fascial space infections of odontogenic origin can be clearly depicted on the USG. The study concluded that different stages of fascial space infections of odontogenic origin can be clearly depicted on the USG and it can be used as a reliable adjunctive imaging technique in the diagnosis of fascial space infection of odontogenic origin.⁶⁶

Prince CN et al (2012) assessed the diagnostic capability of real-time ultrasound imaging, together with the application of color power Doppler in the identification and differential diagnosis of the periapical lesions. Fifteen patients with periapical lesions of pulpal origin, diagnosed with clinical and conventional radiographic examination, were examined further using ultrasonography. The results from the biopsies of the lesions were compared and statistically analyzed. The differential diagnosis between periapical granulomas and cystic lesions, which were based on the ultrasonographic findings, were confirmed by the results of the histopathologic examination in 13 (86.7%) of 15 cases, one being granuloma and 14 being cystic lesion.⁶⁷

Sumit Goel et al (2011) evaluated the efficacy of ultrasonography with color Doppler and power Doppler applications over conventional radiography in the diagnosis of periapical lesions.Thirty patients having inflammatory periapical lesions of the maxillary or mandibular anterior teeth and requiring endodontic surgery were selected for inclusion in this study. All patients consented to participate in the study. They used conventional periapical radiographs as well as USG with color Doppler and power Doppler for the diagnosis of these lesions. Their diagnostic performances were compared against histopathologic examination. All data were compared and statistically analyzed.USG examination with color Doppler and power Doppler identified 29 (19 cysts and 10 granulomas) of 30 periapical lesions accurately, with a sensitivity of 100% for cysts and 90.91% for granulomas and a specificity of 90.91% for cysts and 100% for granulomas. In comparison, conventional intraoral radiography identified only 21 lesions (sensitivity of 78.9% for cysts and 45.4% for granulomas and specificity of 45.4% for cysts and 78.9% for granulomas). There was definite correlation between the echo texture of the lesions and the histopathological features except in one case.68

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