untitled Introduction The advent of multislice computerised tomography (CT) has resulted in a huge step in diagnostic accuracy due to better image quality, multiplanar capabilities and faster speed of the scans. Pseudolesions are not unknown in radiology or in CT imag- ing. However the observation of some arte- facts, especially the flow-related ones, has increased with the faster scanning. Lack of familiarity with these new pseudolesions can lead to misdiagnoses. Pseudolesions The lesions described below are noted frequently during imaging. This pictorial essay aimed at highlighting them as some of these lesions still confound junior staff, especially in their early learning curve. The commonly viewed pseudolesions are as follows: Azygos vein In the newer multislice scanners con- trast is now routinely seen in the major thoracic arteries and veins without opacifi- cation of the azygos vein (Fig. 1). This is because of delayed filling of the azygous vein. This leads to the impression of a mass or a node in this location especially if the vein is dilated.1 However the location, shape and the relationship to the superior vena cava are clues that the ‘lesion’ is the unopacified azygous vein. If there is doubt a delayed scan usually clarifies things. Pulmonary veins The unopacified portions of the right and left superior pulmonary veins can be mistaken for nodes in the hila (Figs 2 and 3).2 The chest scan must be prolonged enough to allow these to fill (30 - 35 sec- onds on 4-slice CT). If the scan is per- formed for diagnosis of pulmonary embo- lus, then both arterial and venous phases must be done to confirm venous emboli. Aorta Motion artefacts can complicate the diagnosis of thoracic aortic dissection.3 Their position in the ascending aorta is predictable and is related to systolic aortic motion from the left anterior to the right posterior position (Fig. 4). Oesophagus Air or contrast in the oesophagus seen on multiple (4 or more) contiguous slices is a sign of motility disorder on single-slice CT.4 On newer scanners, due to fast speed, the oesophagus can be imaged during a sin- gle swallow, thus air in the oesophagus is not abnormal (Fig. 5). However large amount of intra-oesophageal air with or without fluid level can still be considered abnormal. Scalloped or nodular appearance of muscular attachments of the diaphragm These were occasionally noted on sin- gle-slice CT in older patients, but are now routinely observed (Fig. 6). These should not be confused with the nodularity of peritoneal deposits. Metastatic nodules change size abruptly on multiple contigu- ous scans, while diaphragm-related nodu- lar invaginations remain smooth on sequential slices.5 Inferior vena cava Laminar flow within the inferior vena cava (IVC) can cause artefacts that may simulate thrombus.6 A ‘pseudothrombus’ artefact within the suprarenal inferior vena cava produced by rapid infusion of contrast material is believed to be from laminar flow of renal venous effluent of increased opaci- PICTORIAL ESSAY 30 SA JOURNAL OF RADIOLOGY • December 2005 Pseudolesions as seen on multislice CT A K Bajwa MB BS, FCRad (SA) Department of Diagnostic Radiology Chris Hani Baragwanath Hospital University of the Witwatersrand Johannesburg Fig. 1. Partly opacified azygous vein due to reflux from superior vena cava can be mistak- en for nodes if unopacified. Fig. 4. Aortic pulsation imitating dissection in the ascending aorta. Fig. 3. Coronal image showing the normal vertical course of the partially opacified vein. Fig. 2. Portion of the right superior pulmonary vein appearing as a lymph node on axial image. 8 copy 12/1/05 12:30 PM Page 30 ty around less opacified infrarenal caval contents (Figs 7 and 8).This artefact, seen in 21% of older CT scans, is now noted routinely. Similar appearances may be encountered in the iliac and femoral veins. Liver and spleen Heterogeneous enhancement in the early arterial phase is normal. The pattern becomes more pronounced with the faster rate of injection.7 Portal venous phase studies should be used to confirm any suspected parenchy- mal perfusion abnormality (e.g. Budd- Chiari syndrome). Similarly, the hepatic veins are hypodense on the arterial phase and can be mistaken for low-density lesions (Figs 9 and 10). The liver study should rou- tinely include triphasic examination for complete evaluation. Uterus There may be transitory subendometri- al and /or myometrial enhancement (in the arterial and parenchymal phase of the scan). This is followed by diffuse enhance- ment on delayed scan (3 minutes or more). These patterns depend on variables such as the menopausal status and age of the patient.8 Knowledge of these normal find- ings might help when confronted with unusual uterine enhancement during rou- tine studies obtained with CT (Fig. 11). Conclusion We have noted some of these common artefacts since the introduction of multi- slice CT in our hospital. Familiarity with these pitfalls and optimal procedural pro- tocols will result in fewer misdiagnoses and prevent radiological embarrassment. References 1. Smathers RL, Buschi AJ, Pope TL jun., Benbridge AN, Williamson BR. The azygous arch: Normal and pathologic CT appearance. Am J Roentgenol 1992; 139: 477-483. 2. Naidich DP, Khouri NF, Scott WW, Wang KP, Siegelman SS. Computed tomography of the pul- monary hila: Normal anatomy. J Comput Assist Tomogr 1981; 5: 459-467. 3. Duvernoy O, Coulden R, Ytterberg C. Aortic motion: a potential pitfall in CT imaging of dissec- tion in the ascending aorta. J Comput Assist Tomogr 1995; 19: 569-572. 4. Bhalla M, Silver RM, Shepard JA, McLoud TC. Chest CT in patients with scleroderma: prevalence of asymptomatic esophageal dilatation and medi- astinal lymphadenopathy. Am J Roentgenol 1993; 161: 269-272. 5. Brink J, Heiken JP, Semenkovich J, Teefey SA, McClennan BL, Sagel SS. Abnormalities of the diaphragm and adjacent structures: Finding on multiplaner spiral CT. Am J Roentgenol 1994; 163: 307-310. 6. McWilliams RG, Chalmers AG. Pseudothrom- bosis of the infra-renal inferior vena cava during helical CT. Clin Radiol 1995; 50: 751-755. 7. Urban BA, Fishman EK. Helical CT of the spleen. Am J Roentgenol 1998; 170: 997-1003. 8. Kaur H, Loyer EM, Minami M, Charnsangavej C. Patterns of uterine enhancement with helical CT. Eur J Radiol. 1998; 28: 250-255. PICTORIAL ESSAY 31 SA JOURNAL OF RADIOLOGY • December 2005 Fig. 5. Air in the oesophagus is routine on multi-detector CT. Fig. 6. The anterior diaphragm can look quite thick as it becomes continuous with the ante- riolateral diaphragm. Fig. 8. A later scan at the same table position. The IVC flow artefact has disappeared. Fig. 7. Pseudothrombus in the IVC. Fig. 10. Delayed scan at the same level show- ing the filling of hepatic veins. Spleen now has uniform enhancement. Fig. 9. Unopacified hepatic veins appearing as hypodense lesions. Note the heterogeneous enhancement of the spleen. Fig. 11. Unusual early uterine enhancement. 8 copy 12/1/05 12:30 PM Page 31