- Email: [email protected]
Intraoperative imaging techniques: A guide to retrieval of foreign bodies
Intraoperative imaging techniques: A guide to retrieval of foreign bodies Pierre-John Holmes, DMD, MD, MPH,a Jason R. Miller, DMD, MD,b Rajesh Gutta, BDS,c and Patrick J. Louis, DDS, MD,d Birmingham, Ala UNIVERSITY OF ALABAMA
Foreign bodies are frequently introduced into the tissues of the head and neck by various mechanisms, and oral and maxillofacial surgeons are often called upon to retrieve these embedded objects. Retrieval may be quite challenging depending on many factors such as the size of the object, the location, and the surrounding anatomical structures. Preoperative imaging is very important in deciding upon the surgical approach. Computerized tomography is considered the gold standard for detection of foreign bodies because of the ability to localize an object in multiple planes and the creation of a 3-dimensional image. Difficulty arises when looking for a small object in an area with multiple important anatomical structures, such as the infratemporal fossa or the neck. Surgery can become tedious secondary to the risk of postoperative morbidity with injury to various anatomical structures. Foreign bodies in the head and neck are often difficult to manage even when a plan has been formulated from static preoperative images. Intraoperative feedback or guidance, especially when navigating through troublesome locations, can be extremely useful. In this paper, we report 2 cases and discuss the various modalities used for intraoperative imaging as a guide for surgical retrieval of foreign bodies. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;100:614-8)
In any penetrating trauma the presence of a foreign body must be considered. Initial aggressive treatment of the entry wound and removal of any foreign matter is important for successful recovery. Blind exploration is often time consuming and sometimes futile, even when a foreign body is known to be present.1 Accurate localization of the foreign body before removal is therefore essential. There are many techniques of localizing an object within soft tissue. These include tagged hemoclips, grid systems, sinography, sonography, fluoroscopy, and stereotactic guides.2-6 Several imaging methods for locating foreign bodies have been used, including plain radiographs, xeroradiographs, computerized tomography (CT), magnetic resonance imaging (MRI), electromagnetic metal detector, and ultrasound (US).7-11 We present 2 cases in which different techniques were used for the retrieval of retained foreign bodies. We will then discuss the advantages and disadvantages of other imaging modalities available. CASE REPORTS Case 1 A 67-year-old male presented to our clinic for a second opinion regarding a needle that broke off while receiving a a
Assistant Professor, Oral & Maxillofacial Surgery. Chief Resident, Oral & Maxillofacial Surgery. c Resident, Oral & Maxillofacial Surgery. d Director, Oral & Maxillofacial Surgery Residency Program. Received for publication Sep 2, 2004; returned for revision Jan 27, 2005; accepted for publication Feb 1, 2005. 1079-2104/$ - see front matter Ó 2005 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2005.02.072 b
614
right inferior alveolar nerve block for a routine dental procedure. This was a 30-gauge needle, which was bent by the dentist prior to administration of local anesthesia. The needle broke off at the hub and was lodged in the right pterygomandibular space. He was immediately transported to his local oral surgeon who attempted to remove the needle under direct visualization and was not successful. The patient then had a second procedure performed under general anesthesia with the aid of C-arm fluoroscopy. This too was unsuccessful. At this point the patient was referred to our office for a second opinion. On presentation, the patient’s only complaint was that of soreness secondary to the previous procedures. He denied sharp or painful sensations with normal jaw functions such as mouth opening or chewing. Clinical examination revealed a well healed incision on the right posterior buccal mucosa, which was mildly tender to palpation and slightly edematous. Deep palpation did not elicit any significant pain or sharp sensation; also no foreign body was palpated. A panoramic radiograph revealed a short 30-gauge needle in the pterygomandibular space lying in a horizontal direction close to the neck of the condyle (Figs 1 and 2). A CT scan with thin slices confirmed the position of the needle (Fig 3). The deepest portion of the needle was at the neck of the condyle and was approximately 4 mm medial to the bone running parallel to the mandible. On the morning of surgery, the patient had a second CT scan performed with appropriate metallic markers placed along the scalp, as well as an intraoral bite block to simulate mandibular position during surgery. This information was fed into the Stealth System (Medtronics, Minneapolis, Minn). The patient was taken to the operating room, where general anesthesia was administered through a nasal endotracheal tube. The patient was positioned and placed in Mayfield pins to completely immobilize the head. The machine was calibrated to the patient’s head position with the use of a nonsterile wand that was touched to the metallic markers. Under sterile conditions,
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Fig 1. Panoramic radiograph demonstrating a retained needle in the right infratemporal fossa.
Fig 2. Needle in the right infratemporal fossa. exploration of the right pterygomandibular space with stealth guidance was performed. The needle was encountered along the medial aspect of the ramus just superior to the sigmoid notch (Fig 4). It was grasped and removed in one piece with a Kelly clamp without further complications. The patient’s postoperative course was unremarkable.
Case 2 A 34-year-old male presented to the University of Alabama at Birmingham emergency department after sustaining a closerange low-velocity gunshot wound to the face. Initially the patient presented with diffuse bleeding from his oral cavity,
Fig 3. CT scan showing the retained needle in the infratemporal fossa.
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616 Holmes et al
Fig 4. Navigation system demonstrating the retained needle in multiple views.
and advanced trauma life support was initiated by the Trauma Surgery service. Intubation with an oral endotracheal tube was performed to secure the airway. Oral and Maxillofacial Surgery was consulted for further management of the injury. Initial examination revealed an entrance wound in the right cheek just below the malar eminence and that there was no exit wound. Further examination of the oral cavity was difficult because of bleeding. Intraoral hemorrhage was initially controlled with packing of the oral cavity. The patient was then sent for C-spine, head, and maxillofacial CT scans for further investigation. The maxillofacial CT revealed a minimally displaced fracture at the right angle of the mandible and a bullet fragment in the area of the base of the tongue. At this time the decision was made to take the patient to the operating room (OR) for wound exploration, hemorrhage control, and definitive airway placement. In the OR, further examination revealed a 4-cm buccal mucosa laceration, a retromolar trigone laceration, and significant edema of the airway and tongue. No bullet fragment could be located at the
base of the tongue. The intraoral wounds were then closed and direct laryngoscopy was performed to rule out other injuries and lacerations. Owing to marked airway edema a tracheostomy was simultaneously performed. Over the next several days the patient was slowly weaned off the ventilator and had an otherwise uneventful course. Because of concern about the bullet fragment migrating to the surface of the tongue and the risk of aspiration, the patient was taken back to the operating room for further exploration and possible retrieval of the bullet fragment. At this time, intraoperative ultrasound-guided bullet retrieval was performed. A high-frequency linear transducer was used from both a submandibular and and intraoral approach to localize the bullet and provide real-time guidance during dissection (Fig 5). The fragment was localized at the junction of the base of the tongue and the floor of mouth, just lateral to the retromolar trigone. The bullet was found approximately 1.5 cm deep to the mucosa of the floor of the mouth and 1 cm lateral to the mandible. The bullet was successfully located and then removed with a hemostat without any complications.
OOOOE Volume 100, Number 5
DISCUSSION Plain film radiography Several methods have been used to locate and retrieve foreign bodies in soft tissues. One of the first described methods was a plain radiograph. Worth11 recommended 2 views at right angles to each other for 3-dimensional localization. The capability of plain films to demonstrate a foreign body depends on the object’s density, size, and orientation with regard to the surrounding tissue. This relative difference in density will determine the degree of visibility of the object with plain film radiography. The majority of foreign bodies are radiopaque and therefore visible on the plain radiographs. However, substances with densities close to that of the soft tissue are not distinguishable from the neighboring tissue, and plain film radiography is of no value in these cases. Advantages of plain film radiography include availability in the operating room to provide static images, low cost, easy interpretation, and its presence at all institutions. Computerized tomography CT is considered the gold standard for detection of foreign bodies. CT can provide multiplanar images when compared to the 2-dimensional plain radiographs. CT is better for exact 3-dimensional location of the foreign body preoperatively. However, the object could potentially move from the time of examination to the time of the operation. The image quality of CT is diminished through patient movement and metallic artifacts. There is also limited soft tissue contrast. Other disadvantages of CT include high cost, increased ionizing radiation, limited availability, and the possible need for anesthesia in pediatric cases. Magnetic resonance imaging MRI gives superior soft tissue contrast compared to other imaging methods. The role of MRI in the detection of foreign bodies is questionable. MRI is not a suitable imaging modality for detecting metallic fragments because it gives rise to powerful interference artifacts and may present potential hazards for the patient, such as movement of the object through the soft tissues.13 It may also interfere with indwelling medical devices (eg, cardiac pacemakers). MRI also has a higher cost and more limited availability than CT. In addition, MRI often does not allow differentiation of foreign bodies that have low signal intensity from other structures that can have low signal intensity, such as scar tissue, tendons, and calcifications.12 Fluoroscopy Intraoperative fluoroscopic imaging is used routinely to provide the surgeon with optical feedback during
Holmes et al 617
Fig 5. Intraoperative ultrasound demonstrating retained bullet.
the percutaneous insertion of surgical instruments. A radiographer acts as the ‘‘interface’’ between the surgeon and fluoroscope as the radiographer moves the device at the surgeon’s command. This procedure is time consuming and vulnerable to communication errors between the surgeon and radiographer. The term fluoroscopy refers to the use of low (ie, 0.5 to 2 mA) continuous radiation exposure. Fluoroscopic systems consist of an x-ray image intensifier coupled to photographic and video cameras. Although C-arms provide very valuable in situ image information, the risk of radiation exposure derived from the use of an image intensifier to the patient and operating room staff is undesirable. The radiation dose is 10-12 times greater than conventional procedures. Furthermore, mobile C-arm fluoroscopy has some limitations. For example, only a single-plane view is available at a given time. In addition, the surgeon’s hands or surgical instruments may interfere with the images of the surgical field. Also, the C-arm needs repeated repositioning for images in different planes and has a cumbersome means of alignment. Ultrasonography Ultrasonography offers excellent 3-dimensional localization that may be used preoperatively or intraoperatively for foreign body retrieval. The location of the foreign body can be defined in relationship to the muscles and tendons. Ultrasonography can detect many radiolucent and radiopaque foreign bodies as well as metals, which produce a characteristic image. Although CT scans have been regarded as the gold standard, a recent study showed that ultrasonography identified 90% of all foreign bodies, whereas CT scans identified only 70%.14 Foreign bodies are usually hyperechoic
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618 Holmes et al (bright or white) and interrupt the normal homogeneous echo texture of the soft tissue. Some materials have characteristic echo patterns, which can alert the ultrasonographer to the presence of a foreign body. Dense echogenic foreign bodies produce reverberations called comet-tail artifacts. Ultrasonography is used in preoperative and intraoperative settings to give 3-dimensional localization of a foreign body. The accurate depth of the foreign body from the skin is indicated in centimeters. The foreign body is located directly underneath the point where a transducer, in a perpendicular orientation, touches the skin. If a foreign body is present in the soft tissues longer than about 24 hours, the ensuing inflammatory reaction can create a hypoechoic rim around the echogenic foreign body. This hypoechoic rim improves the sensitivity and specificity of the ultrasonographic examination.12 Intraoperative ultrasonography has been found to be a great tool for foreign body localization and it does not carry the risk of significant irradiation. It offers the advantages of quick access, high local resolution, choice of images, and tracking of anatomical structures. The disadvantages are the dependence on the examiner, geometrical distortions, and the associated noise. Stereotactic systems Horsley and Clarke first used intraoperative imaging with the aid of stereotactic systems in neurosurgery.7 The stereotactic frames allowed the localization of deep-seated intracranial structures. Transition from the computer-assisted plan to the operative phase is based on frameless navigation and localization techniques. This allows the surgeon to see the actual instrument position on the 3-dimensional reconstructed image data set of the patient. It is also possible to determine the position of a pathologic or anatomic structure shown in the images of the operative site. The accuracy of these systems is substantially higher in rigid structures such as bones and osseous areas than in soft tissue areas.8 Computer-assisted 3-dimensional guidance systems have the potential for simplifying complex or minimally invasive procedures and reducing postoperative morbidity. Imaging modalities have been linked to surgical instruments to generate a new type of environment, in which the surgeon is provided with information on deep tissue structures.10 It has also been very useful in localization of foreign bodies and pathologic structures because it enables the surgeon to have a precise intraoperative realization in 3 dimensions of the anatomical position in relation to surrounding structures. The limitations of these navigational systems are
expense, limited availability, and the need to obtain a prior CT scan. CONCLUSION Intraoperative imaging can be a great aid in the retrieval of foreign bodies in the maxillofacial region. The surgical intervention can be minimized, allowing safe and precise removal of the foreign bodies. The 2 cases presented here demonstrate the use of real-time ultrasound and CT guidance systems for the removal of foreign bodies. Of the 2 methods, ultrasound imaging is less expensive and more readily available, but the CT-guided systems provide more detail, especially in complex anatomic locations. REFERENCES 1. Pons PT. Foreign bodies. In: Rosen P, editor. Emergency medicine concepts and clinical practice, Vol 1. 4th ed. St Louis: Mosby Year Book; 1998. p. 861-77. 2. McFadden JT. Stereotaxic pinpointing of foreign bodies in the limbs. Ann Surg 1972;175:81-5. 3. Mladick RA. Easy location of foreign body with ‘‘tagged hemoclips.’’ Plast Reconstr Surg 1978;61:459-60. 4. Weinstock RE. Noninvasive technique for the localization of radiopaque foreign bodies. J Foot Surg 1981;20:73-5. 5. Kleiman MB, Elfenbein DS, Wolf EL, Hemphill M, Kurlinski JP. Periosteal reaction due to foreign body induced inflammation of soft tissue. Pediatrics 1977;60:638-41. 6. Bhavsar MS. Technique of finding a metallic foreign body. Am J Surg 1981;141:305. 7. Veselko M, Trobec R. Intraoperative localization of retained metallic fragments in missile wounds. J Trauma 2000;49:1052-8. 8. Charney DB, Manzi JA, Turlik M, Young M. Nonmetallic foreign bodies in the foot: radiography versus xeroradiography. J Foot Surg 1986;25:44-9. 9. Ginsburg MJ, Ellis GL, Flom LL. Detection of soft-tissue foreign bodies by plain radiography, xerography, computed tomography and ultrasonography. Ann Emerg Med 1990;19:701-3. 10. Glatt HJ, Custer PL, Barrett L, Sartor K. Magnetic resonance imaging and computed tomography in a model of wooden foreign bodies in the orbit. Ophthal Plast Reconstr Surg 1990;6: 108-14. 11. Worth HM. Foreign bodies. In: Worth HM, editor. Principles and practice of oral radiologic interpretation. Chicago: Yearbook Medical; 1963. p. 207-12. 12. Jacobson JA, Powell A, Craig JG, Bouffard JA, van Holsbeeck MT. Wooden foreign bodies in soft tissue: detection at ultrasonography. Radiology 1998;206:45-8. 13. Cakir B, Atkan M, Yildirim S, Akoz T. Localization and removal of ferromagnetic foreign bodies by magnet. Ann Plast Surg 2002; 49:541-4. 14. Schlager D. Ultrasound detection of foreign bodies and procedure guidance. Emerg Med Clin N Am 1997;15:895-912. Reprint requests: Dr Jason Russel Miller, DMD, MD SDB 419 1919 7th Avenue South Birmingham, AL 35294-00007 [email protected]
Foreign bodies are frequently introduced into the tissues of the head and neck by various mechanisms, and oral and maxillofacial surgeons are often called upon to retrieve these embedded objects. Retrieval may be quite challenging depending on many factors such as the size of the object, the location, and the surrounding anatomical structures. Preoperative imaging is very important in deciding upon the surgical approach. Computerized tomography is considered the gold standard for detection of foreign bodies because of the ability to localize an object in multiple planes and the creation of a 3-dimensional image. Difficulty arises when looking for a small object in an area with multiple important anatomical structures, such as the infratemporal fossa or the neck. Surgery can become tedious secondary to the risk of postoperative morbidity with injury to various anatomical structures. Foreign bodies in the head and neck are often difficult to manage even when a plan has been formulated from static preoperative images. Intraoperative feedback or guidance, especially when navigating through troublesome locations, can be extremely useful. In this paper, we report 2 cases and discuss the various modalities used for intraoperative imaging as a guide for surgical retrieval of foreign bodies. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;100:614-8)
In any penetrating trauma the presence of a foreign body must be considered. Initial aggressive treatment of the entry wound and removal of any foreign matter is important for successful recovery. Blind exploration is often time consuming and sometimes futile, even when a foreign body is known to be present.1 Accurate localization of the foreign body before removal is therefore essential. There are many techniques of localizing an object within soft tissue. These include tagged hemoclips, grid systems, sinography, sonography, fluoroscopy, and stereotactic guides.2-6 Several imaging methods for locating foreign bodies have been used, including plain radiographs, xeroradiographs, computerized tomography (CT), magnetic resonance imaging (MRI), electromagnetic metal detector, and ultrasound (US).7-11 We present 2 cases in which different techniques were used for the retrieval of retained foreign bodies. We will then discuss the advantages and disadvantages of other imaging modalities available. CASE REPORTS Case 1 A 67-year-old male presented to our clinic for a second opinion regarding a needle that broke off while receiving a a
Assistant Professor, Oral & Maxillofacial Surgery. Chief Resident, Oral & Maxillofacial Surgery. c Resident, Oral & Maxillofacial Surgery. d Director, Oral & Maxillofacial Surgery Residency Program. Received for publication Sep 2, 2004; returned for revision Jan 27, 2005; accepted for publication Feb 1, 2005. 1079-2104/$ - see front matter Ó 2005 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2005.02.072 b
614
right inferior alveolar nerve block for a routine dental procedure. This was a 30-gauge needle, which was bent by the dentist prior to administration of local anesthesia. The needle broke off at the hub and was lodged in the right pterygomandibular space. He was immediately transported to his local oral surgeon who attempted to remove the needle under direct visualization and was not successful. The patient then had a second procedure performed under general anesthesia with the aid of C-arm fluoroscopy. This too was unsuccessful. At this point the patient was referred to our office for a second opinion. On presentation, the patient’s only complaint was that of soreness secondary to the previous procedures. He denied sharp or painful sensations with normal jaw functions such as mouth opening or chewing. Clinical examination revealed a well healed incision on the right posterior buccal mucosa, which was mildly tender to palpation and slightly edematous. Deep palpation did not elicit any significant pain or sharp sensation; also no foreign body was palpated. A panoramic radiograph revealed a short 30-gauge needle in the pterygomandibular space lying in a horizontal direction close to the neck of the condyle (Figs 1 and 2). A CT scan with thin slices confirmed the position of the needle (Fig 3). The deepest portion of the needle was at the neck of the condyle and was approximately 4 mm medial to the bone running parallel to the mandible. On the morning of surgery, the patient had a second CT scan performed with appropriate metallic markers placed along the scalp, as well as an intraoral bite block to simulate mandibular position during surgery. This information was fed into the Stealth System (Medtronics, Minneapolis, Minn). The patient was taken to the operating room, where general anesthesia was administered through a nasal endotracheal tube. The patient was positioned and placed in Mayfield pins to completely immobilize the head. The machine was calibrated to the patient’s head position with the use of a nonsterile wand that was touched to the metallic markers. Under sterile conditions,
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Holmes et al 615
Fig 1. Panoramic radiograph demonstrating a retained needle in the right infratemporal fossa.
Fig 2. Needle in the right infratemporal fossa. exploration of the right pterygomandibular space with stealth guidance was performed. The needle was encountered along the medial aspect of the ramus just superior to the sigmoid notch (Fig 4). It was grasped and removed in one piece with a Kelly clamp without further complications. The patient’s postoperative course was unremarkable.
Case 2 A 34-year-old male presented to the University of Alabama at Birmingham emergency department after sustaining a closerange low-velocity gunshot wound to the face. Initially the patient presented with diffuse bleeding from his oral cavity,
Fig 3. CT scan showing the retained needle in the infratemporal fossa.
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616 Holmes et al
Fig 4. Navigation system demonstrating the retained needle in multiple views.
and advanced trauma life support was initiated by the Trauma Surgery service. Intubation with an oral endotracheal tube was performed to secure the airway. Oral and Maxillofacial Surgery was consulted for further management of the injury. Initial examination revealed an entrance wound in the right cheek just below the malar eminence and that there was no exit wound. Further examination of the oral cavity was difficult because of bleeding. Intraoral hemorrhage was initially controlled with packing of the oral cavity. The patient was then sent for C-spine, head, and maxillofacial CT scans for further investigation. The maxillofacial CT revealed a minimally displaced fracture at the right angle of the mandible and a bullet fragment in the area of the base of the tongue. At this time the decision was made to take the patient to the operating room (OR) for wound exploration, hemorrhage control, and definitive airway placement. In the OR, further examination revealed a 4-cm buccal mucosa laceration, a retromolar trigone laceration, and significant edema of the airway and tongue. No bullet fragment could be located at the
base of the tongue. The intraoral wounds were then closed and direct laryngoscopy was performed to rule out other injuries and lacerations. Owing to marked airway edema a tracheostomy was simultaneously performed. Over the next several days the patient was slowly weaned off the ventilator and had an otherwise uneventful course. Because of concern about the bullet fragment migrating to the surface of the tongue and the risk of aspiration, the patient was taken back to the operating room for further exploration and possible retrieval of the bullet fragment. At this time, intraoperative ultrasound-guided bullet retrieval was performed. A high-frequency linear transducer was used from both a submandibular and and intraoral approach to localize the bullet and provide real-time guidance during dissection (Fig 5). The fragment was localized at the junction of the base of the tongue and the floor of mouth, just lateral to the retromolar trigone. The bullet was found approximately 1.5 cm deep to the mucosa of the floor of the mouth and 1 cm lateral to the mandible. The bullet was successfully located and then removed with a hemostat without any complications.
OOOOE Volume 100, Number 5
DISCUSSION Plain film radiography Several methods have been used to locate and retrieve foreign bodies in soft tissues. One of the first described methods was a plain radiograph. Worth11 recommended 2 views at right angles to each other for 3-dimensional localization. The capability of plain films to demonstrate a foreign body depends on the object’s density, size, and orientation with regard to the surrounding tissue. This relative difference in density will determine the degree of visibility of the object with plain film radiography. The majority of foreign bodies are radiopaque and therefore visible on the plain radiographs. However, substances with densities close to that of the soft tissue are not distinguishable from the neighboring tissue, and plain film radiography is of no value in these cases. Advantages of plain film radiography include availability in the operating room to provide static images, low cost, easy interpretation, and its presence at all institutions. Computerized tomography CT is considered the gold standard for detection of foreign bodies. CT can provide multiplanar images when compared to the 2-dimensional plain radiographs. CT is better for exact 3-dimensional location of the foreign body preoperatively. However, the object could potentially move from the time of examination to the time of the operation. The image quality of CT is diminished through patient movement and metallic artifacts. There is also limited soft tissue contrast. Other disadvantages of CT include high cost, increased ionizing radiation, limited availability, and the possible need for anesthesia in pediatric cases. Magnetic resonance imaging MRI gives superior soft tissue contrast compared to other imaging methods. The role of MRI in the detection of foreign bodies is questionable. MRI is not a suitable imaging modality for detecting metallic fragments because it gives rise to powerful interference artifacts and may present potential hazards for the patient, such as movement of the object through the soft tissues.13 It may also interfere with indwelling medical devices (eg, cardiac pacemakers). MRI also has a higher cost and more limited availability than CT. In addition, MRI often does not allow differentiation of foreign bodies that have low signal intensity from other structures that can have low signal intensity, such as scar tissue, tendons, and calcifications.12 Fluoroscopy Intraoperative fluoroscopic imaging is used routinely to provide the surgeon with optical feedback during
Holmes et al 617
Fig 5. Intraoperative ultrasound demonstrating retained bullet.
the percutaneous insertion of surgical instruments. A radiographer acts as the ‘‘interface’’ between the surgeon and fluoroscope as the radiographer moves the device at the surgeon’s command. This procedure is time consuming and vulnerable to communication errors between the surgeon and radiographer. The term fluoroscopy refers to the use of low (ie, 0.5 to 2 mA) continuous radiation exposure. Fluoroscopic systems consist of an x-ray image intensifier coupled to photographic and video cameras. Although C-arms provide very valuable in situ image information, the risk of radiation exposure derived from the use of an image intensifier to the patient and operating room staff is undesirable. The radiation dose is 10-12 times greater than conventional procedures. Furthermore, mobile C-arm fluoroscopy has some limitations. For example, only a single-plane view is available at a given time. In addition, the surgeon’s hands or surgical instruments may interfere with the images of the surgical field. Also, the C-arm needs repeated repositioning for images in different planes and has a cumbersome means of alignment. Ultrasonography Ultrasonography offers excellent 3-dimensional localization that may be used preoperatively or intraoperatively for foreign body retrieval. The location of the foreign body can be defined in relationship to the muscles and tendons. Ultrasonography can detect many radiolucent and radiopaque foreign bodies as well as metals, which produce a characteristic image. Although CT scans have been regarded as the gold standard, a recent study showed that ultrasonography identified 90% of all foreign bodies, whereas CT scans identified only 70%.14 Foreign bodies are usually hyperechoic
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618 Holmes et al (bright or white) and interrupt the normal homogeneous echo texture of the soft tissue. Some materials have characteristic echo patterns, which can alert the ultrasonographer to the presence of a foreign body. Dense echogenic foreign bodies produce reverberations called comet-tail artifacts. Ultrasonography is used in preoperative and intraoperative settings to give 3-dimensional localization of a foreign body. The accurate depth of the foreign body from the skin is indicated in centimeters. The foreign body is located directly underneath the point where a transducer, in a perpendicular orientation, touches the skin. If a foreign body is present in the soft tissues longer than about 24 hours, the ensuing inflammatory reaction can create a hypoechoic rim around the echogenic foreign body. This hypoechoic rim improves the sensitivity and specificity of the ultrasonographic examination.12 Intraoperative ultrasonography has been found to be a great tool for foreign body localization and it does not carry the risk of significant irradiation. It offers the advantages of quick access, high local resolution, choice of images, and tracking of anatomical structures. The disadvantages are the dependence on the examiner, geometrical distortions, and the associated noise. Stereotactic systems Horsley and Clarke first used intraoperative imaging with the aid of stereotactic systems in neurosurgery.7 The stereotactic frames allowed the localization of deep-seated intracranial structures. Transition from the computer-assisted plan to the operative phase is based on frameless navigation and localization techniques. This allows the surgeon to see the actual instrument position on the 3-dimensional reconstructed image data set of the patient. It is also possible to determine the position of a pathologic or anatomic structure shown in the images of the operative site. The accuracy of these systems is substantially higher in rigid structures such as bones and osseous areas than in soft tissue areas.8 Computer-assisted 3-dimensional guidance systems have the potential for simplifying complex or minimally invasive procedures and reducing postoperative morbidity. Imaging modalities have been linked to surgical instruments to generate a new type of environment, in which the surgeon is provided with information on deep tissue structures.10 It has also been very useful in localization of foreign bodies and pathologic structures because it enables the surgeon to have a precise intraoperative realization in 3 dimensions of the anatomical position in relation to surrounding structures. The limitations of these navigational systems are
expense, limited availability, and the need to obtain a prior CT scan. CONCLUSION Intraoperative imaging can be a great aid in the retrieval of foreign bodies in the maxillofacial region. The surgical intervention can be minimized, allowing safe and precise removal of the foreign bodies. The 2 cases presented here demonstrate the use of real-time ultrasound and CT guidance systems for the removal of foreign bodies. Of the 2 methods, ultrasound imaging is less expensive and more readily available, but the CT-guided systems provide more detail, especially in complex anatomic locations. REFERENCES 1. Pons PT. Foreign bodies. In: Rosen P, editor. Emergency medicine concepts and clinical practice, Vol 1. 4th ed. St Louis: Mosby Year Book; 1998. p. 861-77. 2. McFadden JT. Stereotaxic pinpointing of foreign bodies in the limbs. Ann Surg 1972;175:81-5. 3. Mladick RA. Easy location of foreign body with ‘‘tagged hemoclips.’’ Plast Reconstr Surg 1978;61:459-60. 4. Weinstock RE. Noninvasive technique for the localization of radiopaque foreign bodies. J Foot Surg 1981;20:73-5. 5. Kleiman MB, Elfenbein DS, Wolf EL, Hemphill M, Kurlinski JP. Periosteal reaction due to foreign body induced inflammation of soft tissue. Pediatrics 1977;60:638-41. 6. Bhavsar MS. Technique of finding a metallic foreign body. Am J Surg 1981;141:305. 7. Veselko M, Trobec R. Intraoperative localization of retained metallic fragments in missile wounds. J Trauma 2000;49:1052-8. 8. Charney DB, Manzi JA, Turlik M, Young M. Nonmetallic foreign bodies in the foot: radiography versus xeroradiography. J Foot Surg 1986;25:44-9. 9. Ginsburg MJ, Ellis GL, Flom LL. Detection of soft-tissue foreign bodies by plain radiography, xerography, computed tomography and ultrasonography. Ann Emerg Med 1990;19:701-3. 10. Glatt HJ, Custer PL, Barrett L, Sartor K. Magnetic resonance imaging and computed tomography in a model of wooden foreign bodies in the orbit. Ophthal Plast Reconstr Surg 1990;6: 108-14. 11. Worth HM. Foreign bodies. In: Worth HM, editor. Principles and practice of oral radiologic interpretation. Chicago: Yearbook Medical; 1963. p. 207-12. 12. Jacobson JA, Powell A, Craig JG, Bouffard JA, van Holsbeeck MT. Wooden foreign bodies in soft tissue: detection at ultrasonography. Radiology 1998;206:45-8. 13. Cakir B, Atkan M, Yildirim S, Akoz T. Localization and removal of ferromagnetic foreign bodies by magnet. Ann Plast Surg 2002; 49:541-4. 14. Schlager D. Ultrasound detection of foreign bodies and procedure guidance. Emerg Med Clin N Am 1997;15:895-912. Reprint requests: Dr Jason Russel Miller, DMD, MD SDB 419 1919 7th Avenue South Birmingham, AL 35294-00007 [email protected]