Neuroradiology
Computed Tomography of Paranasal Sinus Tumors 1 Colin Parsons, M.B., F.R.C.S., F.R.C.R., and Neil Hodson, B.Sc., M.B., Ch.B., F.R.C.R.2
Thirty-two patients with histologically proved malignant disease involving the paranasal sinuses were studied by CT. The radiological features of tumor were sinus opacification, a soft-tissue mass, bone erosion and/or displacement, sclerosis, and new-bone formation. Measurements of tissue densities were not helpful in distinguishing tumor from benign disease. Significantly greater tumor extent was demonstrated by CT than by conventional methods in 15 patients; the additional tumor most commonly involved the pterygoid region or orbit. The clinical importance of various directions 01 tumor spread is emphasized. INDEX TERMS: Sinuses, computed tomography, 2[3].1211 • Sinuses, tissue neoplasm, 2[3].370)
paranasal (Paranasal
sinuses, malig. soft
Radiology 132:641-645, September 1979
EMONSTRATION of the true local extent of paranasal sinus tumors is essential in choosing the appropriate treatment modality. Since clinical assessmentis hampered by the surrounding bony structures, diagnostic radiology is of paramount importance. Conventional techniques can demonstrate tumor within the paranasal sinuses and nasal airways, as well as gross bone destruction, but soft-tissue tumor extendingposteriorly and superiorly from the sinuses is frequently not discovered, leading to inappropriate attempts at radical surgery. Involvementof the infratemporal fossa, posterior ethmoid air cells, orbital apex, cribriform plate, nasopharynx, sphenoid sinus, or base of the skull is virtually impossible to eradicate surgically (1). The present study was undertaken to determine whether computed. tomography (CT), which allows the demonstration of soft-tissue planes in the face and orbit and may give evidence of intracranial extension while at the same time demonstrating bony structures, is a more accurate method of staging paranasal sinus tumors. We have adopted the staging criteria proposed by Harrison (1) for tumors of the maXillary antrum, which is based on the prognostic importance of certain directions of tumor extension and in principle is applicable to tumors of the other paranasal sinuses. According to this system, T1 tumors are confined to the mucosa; T2 tumors produce bone erosion; T3 tumors involve the skin, orbit, and ethmoid sinus; and T4 tumors extend to the nasopharynx, sphenoid sinus, cribriform plate, and pterygoid fossa.
D
MATERIAL AND METHODS
Thirty-two patients (12 females and 20 males) 9 to 81 years of age were referred to Royal MarsdenHospital with histologically proved malignant disease involving the paranasaf sinuses. The wide range of tumor types is recorded in TABLE I. Eight patients had undergone unsuc-
T ABLE I: HISTOLOGICAL DIAGNOSIS
No. of cases Squamous-cell carcinoma Adenoid cystic carcinoma Adenocarcinoma Olfactory neuroblastoma Osteosarcoma Lymphoma EmbryonaJ-celJ rhabdomyosarcoma Angiofibroma Melanoma Fibrosarcoma Secondary fibrosarcoma Direct invasion by parotid pleomorphic adenoma Direct invasion bymeningioma
11 4 1 3 3 3 1 i 1 1 1 1 1
cessful attempts at curative surgery before referral to this specialized cancer center. Four patients had received radical radiotherapy or chemotherapy prior to computed tomography. Conventional radiographs and findings on physical examination during anesthesia were available for comparison with the CT findings in most cases. All patients were examined with an EMI CT 5005 general-purpose scanner (2, 3), using the 25.4-cm (1O-in.) ring, 1.3 cm collimation, and the 320 X 320 matrix; this allowed us to obtain images in enlarged 160 X 160 quadrants, which proved to be the most useful presentation. As there was no diagnostically significant difference in signal-to-noise ratio between the 20- and 70-second scan speeds, the faster speed was used. The boundary of the area to be examined, the angle of the head which best demonstrated the relevant anatomy, and the spacing of the tomographic slices were marked on a preliminary lateral radiograph of the head and neck. This was used as a guide to the technician conducting the examination and later as an aid to the clinician in interpretation of the scans. Scans were routinely obtained
1 From the Department ofDiagnostic Radiology and Institute ofCancer Research, Royal Marsden Hospital, Sutton, Surrey, England. Presented at the Sixty-fourth Scientific Assembly and Annual Meeting of the Radiological Society of North America, Chicago, 111., Nov. 26-Dec. 1, 1978. Received Dec. 5, 1978 and accepted Feb. 6, 1979. . 2 Supported bythe Cancer Research Campaign. sjh
641
642
COLIN PARSONS AND NEIL HODSON
Fig. 1. Olfactory neuroblastoma of the left maxillary antrum causing complete opacification of the sinus and displacing the posterolateral bony wall (open arrow) and the nasal septum (closed arrow).
September 1979
Fig. 2. Advanced squamous-cell carcinoma with residual air in the antrum. There is extensive permeated bone destruction of the antral wan and pterygoid plates (black arrows). The tissue planes are obliterated by tumor (white arrows).
li9"Ulh: Fig. 3. Advanced squamous-cell carcinoma of the right maxillary antrum extending posteriorly into the infratemporal fossa, anteriorly into the cheek (arrows), and medially to fill the nasal airway.
parallel to the hard palate at 1.5-cm intervals. Data were analyzed on an independent viewing console. Scans were viewed immediately following the examination so that sections of adjacent areas, at different angles, or after injection of intravenous contrast medium could be obtained before the patient was taken off the scanner. Since the disease was advanced in many cases, surgical correlation was not obtained. Most patients received radiotherapy. RESULTS
Sinus opacification was found in all untreated patients (Fig. 1). The mean density of the soft-tissure tumors fell in the range of 30-90 H (15-45 EMI units), which also included the mean density of benign mucosal swelling and fluid within the antra as noted by Forbes et al. (4). Air was
Fig. 4. Squamous-cell carcinoma of the nasopharynx extending into the pterygoid region. The lesion obliterates the fat plane (closed arrow), while it is preserved on the opposite side (open arrow).
seen within the tumor in 4 untreated patients and appeared in 5 others only after radiotherapy (Fig. 2). A soft-tissue mass extending beyond the bony confines of the sinus was found in all but 2 untreated patients. In 16 cases tumor extended posteriorly from the maxillary antrum into the infratemporal fossa (Fig. 3). The nasal cavity was involved in 14, the nasopharynx in 7, the orbit in 10, and the facial skin in 11. In the infratemporal fossa and parapharyngeal space, tumor could be recognized as a well-defined mass or simply as loss of soft-tissue planes between the muscles and the surrounding fat (Fig. 4). Enhancement following intravenous contrast injection was of very little help in the delineation of paranasal sinus tumors. Although on occasion there was a slight increase in density as a result of the contrast medium, further facial tumor was not found. However, intracranial extension of one squamous-cell carcinoma was visible solely as a result of enhancement (Fig. 5).
Vol. 132
COMPUTED TOMOGRAPHY OF PARANASAL SINUS TUMORS
Fig. 5. Squamous-cell carcinoma of the nasopharynx extending into the middle fossa (large arrow) in a 14-year-old boy. The tumor is shown only after contrast enhancement. Tumor is also causing widening of the optic canal (small arrow).
Fig. 7. Coronal view of a long-standing nasal angiofibroma displacing the nasal septum and orbital floor (arrowheads).
A number of bone abnormalities were found. The most common was bone erosion in some part of the sinus wall, pterygoid plates, or base of the skull (Fig. 6). Long-standing, slowly expanding tumors displaced the sinus walls and nasal septum (Fig. 7). Pressure by such tumors was often associated with clearly defined bone destruction. Sclerosis was seen in only 4 patients. In 3 of them the pterygoid plates were sclerotic when extensive erosion of the adjacent maxilla was present. The other patient showed very dense sclerosis of the posterior antral wall following neutron therapy (Fig. 8). New-bone formation was found only in the three primary osteosarcomas of the maxilla (Fig. 9). The bony element was sharply defined and easily demonstrated in each case, but the boundaries of associated soft-tissue tumor were far less precise (Fig. 10). Significantly more extensive tumor was detected by CT than by conventional methods in 15 of the 32 patients. In nearly all cases, the additional information concerned
643
Neuroradiology
Fig. 6. Squamous-cellcarcinoma of the maxillary antrum, causing permeated bone destruction (arrows).
Fig. 8. Arrow indicates sclerosis of the posterior antral wall following neutron therapy of an adenoid cystic tumor of the left maxillary antrum.
extension posteriorly into the infratemporal or pterygopalatine fossae. Three patients had unexpected orbital involvement, with tumor reaching only as far as the medial rectus muscle (Fig. 11). In another patient, minor sphenoid sinus involvement, not shown by conventional tomography, was found. Of the 22 tumors arising originally within the maxillary antrum, one was unstageabledue to previous radiotherapy. Of the remaining 21, 14 were Stage T4, 5 were Stage T3, and 2 were Stage T2. DISCUSSION Fewer than 10% of patients with malignant disease of the paranasal sinuses have lymph-node metastases at presentation, and even fewer subsequently exhibit distant metastases (1). Local tumor extension must be defined accurately so that operability can be determined or the
644
COLIN PARSONS AND NEIL HODSON
September 1979
Fig. 10. Extensive primary osteosarcoma of the maxilla (open arrow) with a soft-tissue component occupying the oropharynx (closed arrow). Fig. 9. Spiculated new-bone formation (arrow) in a primary osteosarcoma of the maxilla.
Fig. 11. Lymphoma occupying the anterior ethmoid air cells and extending through the medial wall of the orbit as far as the medial rectus muscle. The fat medial to the rectus muscle on the normal side is indicated by the arrows.
adequacy of radiotherapy fields assessed. Conventional radiological techniques and examination under anesthesia together show the degree of bone destruction and the gross extent of soft-tissue tumor but often underestimate the degree of involvement of surrounding structures, which is only determined later at operation. The sites of greatest importance in this respect are the pterygoid region, nasopharynx, sphenoid sinus, posterior ethmoid air cells, cribriform plate, orbital apex, and base of the skull. Since tumors confined within a sinus produce symptoms identical to benign disease, these important areas are commonly involved by the time the patient is referred for assessment, as illustrated by the large number of Stage T4 antral tumors in this series. The sensitivity of CT enables the soft tissues of the pterygoid region, parapharyngeal space, and orbit to be
clearly demonstrated. Soft-tissue tumor extending into these regions as a mass or infiltrating and destroying the tissue planes can be clearly shown. However, mean density measurements have proved nonspecific, so that we have been unable to distinguish between tumor, benign disease, and fluid in the maxillary antrum by this parameter alone. Opacification of contiguous sinuses may indicate that tumor has spread from one to the other or that the ostium is blocked by the tumor mass, causing retention of secretions within the other sinus. This is particularly common when tumor extends into the apex of the nasal airway, obstructing the ethmoid air cells. Repeat scans after radiotherapy may give more accurate assessment of tumor extent; the tumor tissue is frequently smaller, allowing the ostia to become reopened and re-establishing drainage. In this way, previously opaque sinuses may become re-aerated, so that more accurate assessment of tumor extent is possible. Increased tumor density following intravenous injection of contrast material was of no value in facial neoplasms, where no additional tumor was demonstrated. However, when the blood/brain barrier was involved, enhancement proved useful. Demonstration of lymph nodes in the neck was facilitated by infusion of contrast medium to increase the density of blood vessels, but the same nodes were already clinically apparent. More recently we have abandoned scanning of the neck as part of the assessment of paranasal sinus tumors. The transverse plane has proved extremely useful, since many of the anatomical structures necessary in staging these tumors are clearly shown. However, thin plates of bone in the same plane as the scan are not demonstrated, so that a coronal scan is necessary to show the orbital floor and cribriform plate (5, 6). As the gantry cannot be tilted, coronal sections with the patient lying prone in an extreme chin-up position can be achieved only in young and relatively well patients. When it has been used, the coronal view has proved extremely helpful. Minor degrees of bone
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COMPUTED TOMOGRAPHY OF PARANASAL SINUS TUMORS
erosion may be missed by CT due to density averaging of all structures in the tomographic section. Orbital invasion from the ethmoid labyrinth or maxilla is common, usually causing clinical signs. CT is the method of choice for visualization of orbital masses (7). Demonstration of tumor extension into the orbit is important in the assessment of operability. Destruction of the intervening bony wall with replacement of the orbital fat by a soft-tissue tumor is the earliest sign of involvement; later, displacement of the globe and muscle cone may occur. Demonstration of tumor extending into the orbit allows the surgeon to plan exenteration as part of a curative operation; when the orbital apex is involved, however, curative resection is impossible. Intracranial extension can be shown most readily by CT. Contrast enhancement should be used whenever symptoms suggest cerebral involvement. Computed tomography correlates well with conventional radiological investigations and clinical assessment. Unsuspected extension into the pterygoid region and orbit can be demonstrated by this technique. CONCLUSION
Computed tomography has proved to be a major advance in the staging of paranasalsinus tumors, particularly in the demonstration of soft-tissue tumor in the pterygoid region and orbit (8). This is of particular value in assessing operability and the adequacy of radiotherapy fields. With experience, the technique has proved reliable; however,
645
Neuroradiology
because of the nature of malignant disease, including microscopic infiltration into surrounding tissues, minor errors in assessment will continue to occur. ACKNOWLEDGMENTS: We are indebted to our colleagues of the Head and Neck Group, Royal Marsden Hospital for their kindness in referring the patients we have studied. We also wish to thank Miss Susan Bolton and Miss Davida Marsden for typing the text. Department of Diagnostic Radiology Royal Marsden Hospital Downs Road Sutton, Surrey England
REFERENCES 1. Harrison DFN: Critical look at the classification of maxillary sinus carcinomata. Ann Otol Rhinol Laryngol 87:3-9, Jan-Feb 1978 2. Hounsfield GN: Computerized transverse axial scanning (tomography): Part I. Description of system. Br J Radiol 46: 1 16-1 022, Dec 1973 3. Hill KR: The EMI-scanner: technical aspects. Br J Hosp Med 11 (Equipment Suppl): 5-10,13, May 1974 4. Forbes WStC, Fawcitt RA, Isherwood I, et al: Computed tomography in the diagnosis of diseases of the paranasal sinuses. Clin RadioI29:501-511, Sep 1978 5. Rothman SLG, Allen WE, Simeone JF: Direct coronal computerized tomography. Comput Tomogr 1:157-165, 1977 6. Tadmor R, Davis KR, Weber AL, et al: Computed tomography of the skull and facial structures: preliminary evaluation of direct coronal sections. Comput Tomogr 1:211-215, 1977 7. Lloyd GAS: The impact of CT scanning and ultrasonography on orbital diagnosis. Clin RadioI28:583-593, Nov 1977 8. Takahashi M, Tamakawa Y, Shindo M, et al: Computed tomography of the paranasal sinuses and their adjacent structures. Comput Tomogr 1:295-310, 1977
°
Computed Tomography of Paranasal Sinus Tumors 1 Colin Parsons, M.B., F.R.C.S., F.R.C.R., and Neil Hodson, B.Sc., M.B., Ch.B., F.R.C.R.2
Thirty-two patients with histologically proved malignant disease involving the paranasal sinuses were studied by CT. The radiological features of tumor were sinus opacification, a soft-tissue mass, bone erosion and/or displacement, sclerosis, and new-bone formation. Measurements of tissue densities were not helpful in distinguishing tumor from benign disease. Significantly greater tumor extent was demonstrated by CT than by conventional methods in 15 patients; the additional tumor most commonly involved the pterygoid region or orbit. The clinical importance of various directions 01 tumor spread is emphasized. INDEX TERMS: Sinuses, computed tomography, 2[3].1211 • Sinuses, tissue neoplasm, 2[3].370)
paranasal (Paranasal
sinuses, malig. soft
Radiology 132:641-645, September 1979
EMONSTRATION of the true local extent of paranasal sinus tumors is essential in choosing the appropriate treatment modality. Since clinical assessmentis hampered by the surrounding bony structures, diagnostic radiology is of paramount importance. Conventional techniques can demonstrate tumor within the paranasal sinuses and nasal airways, as well as gross bone destruction, but soft-tissue tumor extendingposteriorly and superiorly from the sinuses is frequently not discovered, leading to inappropriate attempts at radical surgery. Involvementof the infratemporal fossa, posterior ethmoid air cells, orbital apex, cribriform plate, nasopharynx, sphenoid sinus, or base of the skull is virtually impossible to eradicate surgically (1). The present study was undertaken to determine whether computed. tomography (CT), which allows the demonstration of soft-tissue planes in the face and orbit and may give evidence of intracranial extension while at the same time demonstrating bony structures, is a more accurate method of staging paranasal sinus tumors. We have adopted the staging criteria proposed by Harrison (1) for tumors of the maXillary antrum, which is based on the prognostic importance of certain directions of tumor extension and in principle is applicable to tumors of the other paranasal sinuses. According to this system, T1 tumors are confined to the mucosa; T2 tumors produce bone erosion; T3 tumors involve the skin, orbit, and ethmoid sinus; and T4 tumors extend to the nasopharynx, sphenoid sinus, cribriform plate, and pterygoid fossa.
D
MATERIAL AND METHODS
Thirty-two patients (12 females and 20 males) 9 to 81 years of age were referred to Royal MarsdenHospital with histologically proved malignant disease involving the paranasaf sinuses. The wide range of tumor types is recorded in TABLE I. Eight patients had undergone unsuc-
T ABLE I: HISTOLOGICAL DIAGNOSIS
No. of cases Squamous-cell carcinoma Adenoid cystic carcinoma Adenocarcinoma Olfactory neuroblastoma Osteosarcoma Lymphoma EmbryonaJ-celJ rhabdomyosarcoma Angiofibroma Melanoma Fibrosarcoma Secondary fibrosarcoma Direct invasion by parotid pleomorphic adenoma Direct invasion bymeningioma
11 4 1 3 3 3 1 i 1 1 1 1 1
cessful attempts at curative surgery before referral to this specialized cancer center. Four patients had received radical radiotherapy or chemotherapy prior to computed tomography. Conventional radiographs and findings on physical examination during anesthesia were available for comparison with the CT findings in most cases. All patients were examined with an EMI CT 5005 general-purpose scanner (2, 3), using the 25.4-cm (1O-in.) ring, 1.3 cm collimation, and the 320 X 320 matrix; this allowed us to obtain images in enlarged 160 X 160 quadrants, which proved to be the most useful presentation. As there was no diagnostically significant difference in signal-to-noise ratio between the 20- and 70-second scan speeds, the faster speed was used. The boundary of the area to be examined, the angle of the head which best demonstrated the relevant anatomy, and the spacing of the tomographic slices were marked on a preliminary lateral radiograph of the head and neck. This was used as a guide to the technician conducting the examination and later as an aid to the clinician in interpretation of the scans. Scans were routinely obtained
1 From the Department ofDiagnostic Radiology and Institute ofCancer Research, Royal Marsden Hospital, Sutton, Surrey, England. Presented at the Sixty-fourth Scientific Assembly and Annual Meeting of the Radiological Society of North America, Chicago, 111., Nov. 26-Dec. 1, 1978. Received Dec. 5, 1978 and accepted Feb. 6, 1979. . 2 Supported bythe Cancer Research Campaign. sjh
641
642
COLIN PARSONS AND NEIL HODSON
Fig. 1. Olfactory neuroblastoma of the left maxillary antrum causing complete opacification of the sinus and displacing the posterolateral bony wall (open arrow) and the nasal septum (closed arrow).
September 1979
Fig. 2. Advanced squamous-cell carcinoma with residual air in the antrum. There is extensive permeated bone destruction of the antral wan and pterygoid plates (black arrows). The tissue planes are obliterated by tumor (white arrows).
li9"Ulh: Fig. 3. Advanced squamous-cell carcinoma of the right maxillary antrum extending posteriorly into the infratemporal fossa, anteriorly into the cheek (arrows), and medially to fill the nasal airway.
parallel to the hard palate at 1.5-cm intervals. Data were analyzed on an independent viewing console. Scans were viewed immediately following the examination so that sections of adjacent areas, at different angles, or after injection of intravenous contrast medium could be obtained before the patient was taken off the scanner. Since the disease was advanced in many cases, surgical correlation was not obtained. Most patients received radiotherapy. RESULTS
Sinus opacification was found in all untreated patients (Fig. 1). The mean density of the soft-tissure tumors fell in the range of 30-90 H (15-45 EMI units), which also included the mean density of benign mucosal swelling and fluid within the antra as noted by Forbes et al. (4). Air was
Fig. 4. Squamous-cell carcinoma of the nasopharynx extending into the pterygoid region. The lesion obliterates the fat plane (closed arrow), while it is preserved on the opposite side (open arrow).
seen within the tumor in 4 untreated patients and appeared in 5 others only after radiotherapy (Fig. 2). A soft-tissue mass extending beyond the bony confines of the sinus was found in all but 2 untreated patients. In 16 cases tumor extended posteriorly from the maxillary antrum into the infratemporal fossa (Fig. 3). The nasal cavity was involved in 14, the nasopharynx in 7, the orbit in 10, and the facial skin in 11. In the infratemporal fossa and parapharyngeal space, tumor could be recognized as a well-defined mass or simply as loss of soft-tissue planes between the muscles and the surrounding fat (Fig. 4). Enhancement following intravenous contrast injection was of very little help in the delineation of paranasal sinus tumors. Although on occasion there was a slight increase in density as a result of the contrast medium, further facial tumor was not found. However, intracranial extension of one squamous-cell carcinoma was visible solely as a result of enhancement (Fig. 5).
Vol. 132
COMPUTED TOMOGRAPHY OF PARANASAL SINUS TUMORS
Fig. 5. Squamous-cell carcinoma of the nasopharynx extending into the middle fossa (large arrow) in a 14-year-old boy. The tumor is shown only after contrast enhancement. Tumor is also causing widening of the optic canal (small arrow).
Fig. 7. Coronal view of a long-standing nasal angiofibroma displacing the nasal septum and orbital floor (arrowheads).
A number of bone abnormalities were found. The most common was bone erosion in some part of the sinus wall, pterygoid plates, or base of the skull (Fig. 6). Long-standing, slowly expanding tumors displaced the sinus walls and nasal septum (Fig. 7). Pressure by such tumors was often associated with clearly defined bone destruction. Sclerosis was seen in only 4 patients. In 3 of them the pterygoid plates were sclerotic when extensive erosion of the adjacent maxilla was present. The other patient showed very dense sclerosis of the posterior antral wall following neutron therapy (Fig. 8). New-bone formation was found only in the three primary osteosarcomas of the maxilla (Fig. 9). The bony element was sharply defined and easily demonstrated in each case, but the boundaries of associated soft-tissue tumor were far less precise (Fig. 10). Significantly more extensive tumor was detected by CT than by conventional methods in 15 of the 32 patients. In nearly all cases, the additional information concerned
643
Neuroradiology
Fig. 6. Squamous-cellcarcinoma of the maxillary antrum, causing permeated bone destruction (arrows).
Fig. 8. Arrow indicates sclerosis of the posterior antral wall following neutron therapy of an adenoid cystic tumor of the left maxillary antrum.
extension posteriorly into the infratemporal or pterygopalatine fossae. Three patients had unexpected orbital involvement, with tumor reaching only as far as the medial rectus muscle (Fig. 11). In another patient, minor sphenoid sinus involvement, not shown by conventional tomography, was found. Of the 22 tumors arising originally within the maxillary antrum, one was unstageabledue to previous radiotherapy. Of the remaining 21, 14 were Stage T4, 5 were Stage T3, and 2 were Stage T2. DISCUSSION Fewer than 10% of patients with malignant disease of the paranasal sinuses have lymph-node metastases at presentation, and even fewer subsequently exhibit distant metastases (1). Local tumor extension must be defined accurately so that operability can be determined or the
644
COLIN PARSONS AND NEIL HODSON
September 1979
Fig. 10. Extensive primary osteosarcoma of the maxilla (open arrow) with a soft-tissue component occupying the oropharynx (closed arrow). Fig. 9. Spiculated new-bone formation (arrow) in a primary osteosarcoma of the maxilla.
Fig. 11. Lymphoma occupying the anterior ethmoid air cells and extending through the medial wall of the orbit as far as the medial rectus muscle. The fat medial to the rectus muscle on the normal side is indicated by the arrows.
adequacy of radiotherapy fields assessed. Conventional radiological techniques and examination under anesthesia together show the degree of bone destruction and the gross extent of soft-tissue tumor but often underestimate the degree of involvement of surrounding structures, which is only determined later at operation. The sites of greatest importance in this respect are the pterygoid region, nasopharynx, sphenoid sinus, posterior ethmoid air cells, cribriform plate, orbital apex, and base of the skull. Since tumors confined within a sinus produce symptoms identical to benign disease, these important areas are commonly involved by the time the patient is referred for assessment, as illustrated by the large number of Stage T4 antral tumors in this series. The sensitivity of CT enables the soft tissues of the pterygoid region, parapharyngeal space, and orbit to be
clearly demonstrated. Soft-tissue tumor extending into these regions as a mass or infiltrating and destroying the tissue planes can be clearly shown. However, mean density measurements have proved nonspecific, so that we have been unable to distinguish between tumor, benign disease, and fluid in the maxillary antrum by this parameter alone. Opacification of contiguous sinuses may indicate that tumor has spread from one to the other or that the ostium is blocked by the tumor mass, causing retention of secretions within the other sinus. This is particularly common when tumor extends into the apex of the nasal airway, obstructing the ethmoid air cells. Repeat scans after radiotherapy may give more accurate assessment of tumor extent; the tumor tissue is frequently smaller, allowing the ostia to become reopened and re-establishing drainage. In this way, previously opaque sinuses may become re-aerated, so that more accurate assessment of tumor extent is possible. Increased tumor density following intravenous injection of contrast material was of no value in facial neoplasms, where no additional tumor was demonstrated. However, when the blood/brain barrier was involved, enhancement proved useful. Demonstration of lymph nodes in the neck was facilitated by infusion of contrast medium to increase the density of blood vessels, but the same nodes were already clinically apparent. More recently we have abandoned scanning of the neck as part of the assessment of paranasal sinus tumors. The transverse plane has proved extremely useful, since many of the anatomical structures necessary in staging these tumors are clearly shown. However, thin plates of bone in the same plane as the scan are not demonstrated, so that a coronal scan is necessary to show the orbital floor and cribriform plate (5, 6). As the gantry cannot be tilted, coronal sections with the patient lying prone in an extreme chin-up position can be achieved only in young and relatively well patients. When it has been used, the coronal view has proved extremely helpful. Minor degrees of bone
Vol. 132
COMPUTED TOMOGRAPHY OF PARANASAL SINUS TUMORS
erosion may be missed by CT due to density averaging of all structures in the tomographic section. Orbital invasion from the ethmoid labyrinth or maxilla is common, usually causing clinical signs. CT is the method of choice for visualization of orbital masses (7). Demonstration of tumor extension into the orbit is important in the assessment of operability. Destruction of the intervening bony wall with replacement of the orbital fat by a soft-tissue tumor is the earliest sign of involvement; later, displacement of the globe and muscle cone may occur. Demonstration of tumor extending into the orbit allows the surgeon to plan exenteration as part of a curative operation; when the orbital apex is involved, however, curative resection is impossible. Intracranial extension can be shown most readily by CT. Contrast enhancement should be used whenever symptoms suggest cerebral involvement. Computed tomography correlates well with conventional radiological investigations and clinical assessment. Unsuspected extension into the pterygoid region and orbit can be demonstrated by this technique. CONCLUSION
Computed tomography has proved to be a major advance in the staging of paranasalsinus tumors, particularly in the demonstration of soft-tissue tumor in the pterygoid region and orbit (8). This is of particular value in assessing operability and the adequacy of radiotherapy fields. With experience, the technique has proved reliable; however,
645
Neuroradiology
because of the nature of malignant disease, including microscopic infiltration into surrounding tissues, minor errors in assessment will continue to occur. ACKNOWLEDGMENTS: We are indebted to our colleagues of the Head and Neck Group, Royal Marsden Hospital for their kindness in referring the patients we have studied. We also wish to thank Miss Susan Bolton and Miss Davida Marsden for typing the text. Department of Diagnostic Radiology Royal Marsden Hospital Downs Road Sutton, Surrey England
REFERENCES 1. Harrison DFN: Critical look at the classification of maxillary sinus carcinomata. Ann Otol Rhinol Laryngol 87:3-9, Jan-Feb 1978 2. Hounsfield GN: Computerized transverse axial scanning (tomography): Part I. Description of system. Br J Radiol 46: 1 16-1 022, Dec 1973 3. Hill KR: The EMI-scanner: technical aspects. Br J Hosp Med 11 (Equipment Suppl): 5-10,13, May 1974 4. Forbes WStC, Fawcitt RA, Isherwood I, et al: Computed tomography in the diagnosis of diseases of the paranasal sinuses. Clin RadioI29:501-511, Sep 1978 5. Rothman SLG, Allen WE, Simeone JF: Direct coronal computerized tomography. Comput Tomogr 1:157-165, 1977 6. Tadmor R, Davis KR, Weber AL, et al: Computed tomography of the skull and facial structures: preliminary evaluation of direct coronal sections. Comput Tomogr 1:211-215, 1977 7. Lloyd GAS: The impact of CT scanning and ultrasonography on orbital diagnosis. Clin RadioI28:583-593, Nov 1977 8. Takahashi M, Tamakawa Y, Shindo M, et al: Computed tomography of the paranasal sinuses and their adjacent structures. Comput Tomogr 1:295-310, 1977
°
