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Spiral CT and ventilation perfusion scintigraphy for the diagnosis of pulmonary embolism
Clinical Radiology (1998) 53, 784-785
Correspondence Letters are published at the discretion of the Editor. Opinions expressed by correspondents are not necessarily those of the Editot: Unduly long letters may be returned to the authors for shortening. Letters in response to a paper may be sent to the author of the paper so that the reply can be published in the same issue. Letters should be typed double spaced and should be signed by all authors personally. References should be given in the style specified in the Instructions to Authors at the front of the Journal.
SPIRAL CT AND VENTILATION PERFUSION SCINTIGRAPHY FOR THE DIAGNOSIS OF P U L M O N A R Y EMBOLISM Sm - Cross et al.'s study raises a number of questions [1]. The first relates to study design. Why did patients proceed to ventilation perfusion scintigraphy (VQS) with its high non-diagnostic rate 'to ensure that pulmonary emboli were not overlooked', rather than performing pulmonary angiography, the accepted gold standard when suspicion of pulmonary ernbolic disease remained after non-confirmatory spiral computed tomographic pulmonary angiography (SCTA)? Furthermore the majority of these cross-over patients had abnormal SCTA which is said to reduce VQS reliability in diagnosing pulmonary emboli (PE) [2]. Alternatively if direct comparison of VQS and SCTA was intended, should not all patients have crossed over? The second relates to the authors' concerns over the morbidity and mortality associated with pulmonary angiography. More recent evaluation suggests angiography is becoming safer with no deaths in 1434 procedures and a major complication rate of 0.3% [3]. The authors rightly praise SCTA's ability to identify an alternative cause for the patient's symptoms. However they did not mention how many of these abnormalities could be deemed from the chest radiograph which is non-specifically abnormal in 84% of patients with and in two-thirds of patients without PE [4]. Were the clinicians aided in their pre-test probability assessment by a plasma D-Dimer? This simple test has a quoted negative predictive value of 91.4% and may have a place in preventing further investigations in low-risk individuals [5]. We remain interested in spiral CT's ascendency over ventilation perfusion scintigraphy in the diagnosis of PE, as in our unit CT became the initial investigation in those with underlying cardio-respiratory disease approximately 1 year ago. This study adds further weight to the growing evidence in favour of SCTA in PE whilst the results of larger trials are awaited. G. BURKILL J'. BELL
Department of Radiology Chelsea and Westminster Hospital London, UK
References 1 Cross JJL, Kemp PM, Walsh CG et al. A randomized trial of spiral CT and ventilation perfusion scintigraphy for the diagnosis of pulmonary embolism. Clinical Radiology 1998;53:177-182. 2 Hansell DM. Spiral computed tomography and pulmonary embolism: current state. Clinical Radiology 1997;52:575-581. 3 Hudson ER, Smith TP, McDermott VG et al. Pulmonary angiography performed with iopamidol: complications in 1,434 patients. Radiology 1996;198:61-65. 4 Stein PD, Terrin ML, Hales CA et al. Clinical, laboratory, roentenographic and electrocardiographic findings in patients with acute pulmonary embolism and no pre-existing cardiac or pulmonary disease [see comments]. Chest 1991;100:598-603. 5 Goldhaber SZ, Simons GR, Elliott CG et al. Quantitative plasma D-dimer levels among patients undergoing pulmonary angiography for suspected pulmonary embolism [see comments]. JAMA 1993;270:2819-2822.
StR- I thank Drs Burkill and Bell for their interest in our study. In reply to their question about study design, patients in whom a definite diagnosis of PE was made at SCTA went on to receive appropriate anticoagulation. If the CT examination was equivocal, VQ scintigraphy was performed to ensure that abnormalities such as perivascular oedema werenot misinterpreted as emboli. Since Goodman et al. have reported that CT has a sensitivity of only 63% for subsegmental emboli [1], patients with normal CT went on to VQ to ensure that small emholi were not overlooked. With regard to their second point, catheter angiography was not used in our study (apart from in two patients with indeterminate SCTA and VQS) since the purpose of our study was to assess the effectiveness of spiral CT 9 1998 The Royal College of Radiologists.
angiography compared with VQ scintigraphy as the initial investigation of PE. Patients were not consented for catheter angiography to avoid bias in the patients entered into the trial. Although the morbidity and mortality of catheter angiography are low, clinicians remain reluctant to refer patients for catheter angiography since it is perceived as an invasive procedure which carries a risk of complications. Patients in the trial were referred for investigation of PE because they had symptoms which were more severe than could be explained by the abnormalities seen on chest radiography. However, CT was able to resolve non-specific shadowing on the chest radiograph into abnormalities such as pleura] effusions or focal areas of consolidation and revealed enlarged mediastinal nodes in one patient and a pulmonary mass in another which were unsuspected on chest radiography. Estimation of plasma D-dimer did not form a part of our study. Although D-dimer shows some promise in selecting patients who merit further investigation, it is not yet universally accepted that the negative predictive values are sufficiently high to exclude PE. There are also logistic problems in performing the assay since this facility is not routinely available in many hospitals. Our study has attempted to investigate the role of CT and VQS in the 'real world' where catheter angiography is not readily available and CT is already swamped with requests. I note that a similar algorithm to that adopted in our paper is already in place in Dr Burkill's department. For departments of many large hospitals where up to 50 VQ scans may be performed a week, changing to spiral CT as the primary investigation of PE is a major undertaking with serious resource implications. We think that our study has provided some evidence on which to base a strategy for the investigation of patients with PE. J.J.L. CROSS
Department of Clinical Radiology Addenbrookes Hospital, Cambridge, UK
Reference 1 Goodman LR, Curtin JJ, Mewissen MW et aL Detection of pulmonary embolism in patients with unresolved clinical and scintigraphic diagnosis: Helical CT versus angiography. American Journal of Roentgenology 1995; 164:1369-1374.
MESENTERIC LIPODYSTROPHY ASSOCIATION WITH R E N A L C E L L CARCINOMA SIR I read with interest the article by Roy et al. [1] describing a case of mesenteric lipodystrophy associated with renal cell carcinoma, and report a similar experience. A 55-year-old man presented with acute onset of right lower quadrant pain. Physical examination revealed a palpable and tender right abdominal mass. Blood tests and colonoscopy were normal. Urinalysis showed numerous red blood cells. A C T scan of the abdomen (Fig. 1) demonstrated a low-attenuation mesenteric lesion displacing the small bowel and colon. There was also evidence of a solid tumour of the right kidney. He underwent a right radical nephrectomy, appendectomy, and biopsy of the mesenteric mass. On histopathology the right kidney tumour was a renal cell carcinoma of the granular cell type. The biopsy of the mesentery showed focal fat necrosis and chronic inflammation, no malignant cells were identified. Mesenteric lipodystrophy is a benign condition. It can occur independently or in association with other disorders including retroperitoneal fibrosis and abdominal malignancies in 30% of cases among which 50% are lymphomas [1,21. The association with urological abnormalities, namely renal cell carcinoma, has only been described in two previous case reports [1,3]. This observation confirms it in another case. The radiologist should be alert for the search of urological malignancies in patients with mesenteric ipodystrophy. -
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M.C. HADDAD
Department of Diagnostic Radiology, American University of Beirut Medical Center Beirut, Lebanon
Correspondence Letters are published at the discretion of the Editor. Opinions expressed by correspondents are not necessarily those of the Editot: Unduly long letters may be returned to the authors for shortening. Letters in response to a paper may be sent to the author of the paper so that the reply can be published in the same issue. Letters should be typed double spaced and should be signed by all authors personally. References should be given in the style specified in the Instructions to Authors at the front of the Journal.
SPIRAL CT AND VENTILATION PERFUSION SCINTIGRAPHY FOR THE DIAGNOSIS OF P U L M O N A R Y EMBOLISM Sm - Cross et al.'s study raises a number of questions [1]. The first relates to study design. Why did patients proceed to ventilation perfusion scintigraphy (VQS) with its high non-diagnostic rate 'to ensure that pulmonary emboli were not overlooked', rather than performing pulmonary angiography, the accepted gold standard when suspicion of pulmonary ernbolic disease remained after non-confirmatory spiral computed tomographic pulmonary angiography (SCTA)? Furthermore the majority of these cross-over patients had abnormal SCTA which is said to reduce VQS reliability in diagnosing pulmonary emboli (PE) [2]. Alternatively if direct comparison of VQS and SCTA was intended, should not all patients have crossed over? The second relates to the authors' concerns over the morbidity and mortality associated with pulmonary angiography. More recent evaluation suggests angiography is becoming safer with no deaths in 1434 procedures and a major complication rate of 0.3% [3]. The authors rightly praise SCTA's ability to identify an alternative cause for the patient's symptoms. However they did not mention how many of these abnormalities could be deemed from the chest radiograph which is non-specifically abnormal in 84% of patients with and in two-thirds of patients without PE [4]. Were the clinicians aided in their pre-test probability assessment by a plasma D-Dimer? This simple test has a quoted negative predictive value of 91.4% and may have a place in preventing further investigations in low-risk individuals [5]. We remain interested in spiral CT's ascendency over ventilation perfusion scintigraphy in the diagnosis of PE, as in our unit CT became the initial investigation in those with underlying cardio-respiratory disease approximately 1 year ago. This study adds further weight to the growing evidence in favour of SCTA in PE whilst the results of larger trials are awaited. G. BURKILL J'. BELL
Department of Radiology Chelsea and Westminster Hospital London, UK
References 1 Cross JJL, Kemp PM, Walsh CG et al. A randomized trial of spiral CT and ventilation perfusion scintigraphy for the diagnosis of pulmonary embolism. Clinical Radiology 1998;53:177-182. 2 Hansell DM. Spiral computed tomography and pulmonary embolism: current state. Clinical Radiology 1997;52:575-581. 3 Hudson ER, Smith TP, McDermott VG et al. Pulmonary angiography performed with iopamidol: complications in 1,434 patients. Radiology 1996;198:61-65. 4 Stein PD, Terrin ML, Hales CA et al. Clinical, laboratory, roentenographic and electrocardiographic findings in patients with acute pulmonary embolism and no pre-existing cardiac or pulmonary disease [see comments]. Chest 1991;100:598-603. 5 Goldhaber SZ, Simons GR, Elliott CG et al. Quantitative plasma D-dimer levels among patients undergoing pulmonary angiography for suspected pulmonary embolism [see comments]. JAMA 1993;270:2819-2822.
StR- I thank Drs Burkill and Bell for their interest in our study. In reply to their question about study design, patients in whom a definite diagnosis of PE was made at SCTA went on to receive appropriate anticoagulation. If the CT examination was equivocal, VQ scintigraphy was performed to ensure that abnormalities such as perivascular oedema werenot misinterpreted as emboli. Since Goodman et al. have reported that CT has a sensitivity of only 63% for subsegmental emboli [1], patients with normal CT went on to VQ to ensure that small emholi were not overlooked. With regard to their second point, catheter angiography was not used in our study (apart from in two patients with indeterminate SCTA and VQS) since the purpose of our study was to assess the effectiveness of spiral CT 9 1998 The Royal College of Radiologists.
angiography compared with VQ scintigraphy as the initial investigation of PE. Patients were not consented for catheter angiography to avoid bias in the patients entered into the trial. Although the morbidity and mortality of catheter angiography are low, clinicians remain reluctant to refer patients for catheter angiography since it is perceived as an invasive procedure which carries a risk of complications. Patients in the trial were referred for investigation of PE because they had symptoms which were more severe than could be explained by the abnormalities seen on chest radiography. However, CT was able to resolve non-specific shadowing on the chest radiograph into abnormalities such as pleura] effusions or focal areas of consolidation and revealed enlarged mediastinal nodes in one patient and a pulmonary mass in another which were unsuspected on chest radiography. Estimation of plasma D-dimer did not form a part of our study. Although D-dimer shows some promise in selecting patients who merit further investigation, it is not yet universally accepted that the negative predictive values are sufficiently high to exclude PE. There are also logistic problems in performing the assay since this facility is not routinely available in many hospitals. Our study has attempted to investigate the role of CT and VQS in the 'real world' where catheter angiography is not readily available and CT is already swamped with requests. I note that a similar algorithm to that adopted in our paper is already in place in Dr Burkill's department. For departments of many large hospitals where up to 50 VQ scans may be performed a week, changing to spiral CT as the primary investigation of PE is a major undertaking with serious resource implications. We think that our study has provided some evidence on which to base a strategy for the investigation of patients with PE. J.J.L. CROSS
Department of Clinical Radiology Addenbrookes Hospital, Cambridge, UK
Reference 1 Goodman LR, Curtin JJ, Mewissen MW et aL Detection of pulmonary embolism in patients with unresolved clinical and scintigraphic diagnosis: Helical CT versus angiography. American Journal of Roentgenology 1995; 164:1369-1374.
MESENTERIC LIPODYSTROPHY ASSOCIATION WITH R E N A L C E L L CARCINOMA SIR I read with interest the article by Roy et al. [1] describing a case of mesenteric lipodystrophy associated with renal cell carcinoma, and report a similar experience. A 55-year-old man presented with acute onset of right lower quadrant pain. Physical examination revealed a palpable and tender right abdominal mass. Blood tests and colonoscopy were normal. Urinalysis showed numerous red blood cells. A C T scan of the abdomen (Fig. 1) demonstrated a low-attenuation mesenteric lesion displacing the small bowel and colon. There was also evidence of a solid tumour of the right kidney. He underwent a right radical nephrectomy, appendectomy, and biopsy of the mesenteric mass. On histopathology the right kidney tumour was a renal cell carcinoma of the granular cell type. The biopsy of the mesentery showed focal fat necrosis and chronic inflammation, no malignant cells were identified. Mesenteric lipodystrophy is a benign condition. It can occur independently or in association with other disorders including retroperitoneal fibrosis and abdominal malignancies in 30% of cases among which 50% are lymphomas [1,21. The association with urological abnormalities, namely renal cell carcinoma, has only been described in two previous case reports [1,3]. This observation confirms it in another case. The radiologist should be alert for the search of urological malignancies in patients with mesenteric ipodystrophy. -
-
M.C. HADDAD
Department of Diagnostic Radiology, American University of Beirut Medical Center Beirut, Lebanon