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ROUTINE THIN SLICE MRI EFFECTIVELY DEMONSTRATES THE LUMBAR PARS INTERARTICULARIS
984
CLINICAL RADIOLOGY
ROUTINE THIN SLICE MRI EFFECTIVELY DEMONSTRATES THE LUMBAR PARS INTERARTICULARIS SIR ± We read with interest the technical report published in Clinical Radiology by Udeshi and Reeves [1], and agree that thin section MRI can effectively demonstrate the normal pars. In our study of asymptomatic volunteers we found that 74% of L4 and L5 pars were type I on 3 mm sagittal T1W images [2]. However, 24% of the pars were classi®ed as type II or sclerotic. The addition of a 3D GRE sequence increases the number of pars classi®ed as type I to 92%. The authors state that a type II pars reliably excludes spondylolysis. This is not the case. Although the majority of pars that appear hypointense will be normal due to either partial volume effects or sclerosis, it is our experience that some spondylolytic defects (both complete and incomplete) will present with a single discrete hypointense band across the pars. There is no evidence to indicate that this appearance can be reliably distinguished from partial volume or sclerosis. Indeed, in the paper by Saifuddin and Burnett [3], four cases showed this appearance, two with a defect and two without. Further clinical studies with CT correlation are required to fully evaluate this appearance of the pars. When speci®c imaging of the pars is required, MRI should ideally demonstrate a type I pars to con®dently exclude a lysis. In our study [2], 92% of pars were graded type I by inclusion of a sagittal 3D GRE sequence, a ®gure which is repeated in an ongoing clinical study. The 3D sequence also allows the user to perform reconstructed reverse angle views if necessary, which is particularly helpful in the upper lumbar spine where we found sagittal images to be less useful. Reverse angled images may also be helpful in excluding fractures elsewhere in the posterior elements such as laminar fractures. The authors also point out that T2W sequences can demonstrate a type I pars. We utilise T2W images to assess for the presence or absence of marrow oedema in acute defects, in which case fat suppression or STIR imaging is preferable. R.S.D. CAMPBELL A.J. GRAINGER
Department of Radiology South Cleveland Hospital Marton Road Middlesbrough TS4 3BW, UK
para 2) and classi®ed such appearances as type 4 (pars defect) rather than types 1 or 2. We can therefore state that in the remaining pars classi®ed as types 1 and 2 spondylolysis is reliably excluded. Our study did not attempt to assess the ef®cacy of MRI for the diagnosis of spondylolysis but only for con®rmation of the normal pars interarticularis in a group of patients not expected to have spondylolyses (by exclusion of such patients by study design). We therefore cannot comment further regarding additional sequences carried out to establish this diagnosis in borderline cases. Our study was an attempt to demonstrate the reliability of a routine lumbar spine MR imaging sequence for the demonstration of the normal pars interarticularis. We remain convinced that thin slice sagittal T1 and T2 weighted images are effective in this aim. U.L. UDESHI D. REEVES
References 1 Udeshi UL, Reeves D. Routine thin slice MRI effectively demonstrates the lumbar pars interarticularis. Clin Radiol 1999;54:615±619. 2 Campbell RSD, Grainger AJ. Optimization of MRI pulse sequences to visualise the normal pars interarticularis. Clin Radiol 1999;54:63±68. 3 Saifuddin A, Burnett SJD. The value of lumbar spine MRI in the assessment of the pars interarticularis. Clin Radiol 1997;52:666±671.
INGUINAL HERNIA ± AN UNUSUAL CAUSE OF BILATERAL RENAL OBSTRUCTION SIR ± We read with interest the article by Bradley et al. [1] describing a case of bilateral hydronephrosis caused by ileal conduit involvement in a right inguinal hernia. We have recently seen a similar case diagnosed using spiral computed tomography (CT) with 3D reconstruction. On this occasion there had been no previous surgery.
References 1 Udeshi UL, Reeves D. Routine thin slice MRI effectively demonstrates the lumbar pars interarticularis. Clin Radiol 1999;54:615±619. 2 Campbell RSD, Grainger AJ. Optimization of MRI pulse sequences to visualise the normal pars interarticularis. Clin Radiol 1999;54:63± 68. 3 Saifuddin A, Burnett SJD. The value of lumbar spine MRI in the assessment of the pars interarticularis. Clin Radiol 1997;52:666±671.
A REPLY SIR ± We thank Drs Campbell and Grainger for their interest in our paper [1]. We have noted the similarity of results in our respective studies [1,2] on T1 weighted imaging of the L4 and L5 pars:
Type 1 Type 2
Udeshi and Reeves [1]
Campbell and Grainger [2]
75% 20%
74% 24%
In the study by Saifuddin and Burnett [3] a small number of pars showed a single discrete hypo-intense band across the pars and had a 50% ®nding of spondylolysis on plain radiographs. For this reason, we modi®ed Saifuddin and Burnett's classi®cation in our study (as stated in our paper ± page 616,
Kidderminster Health Care NHS Trust Bewdley Road Kidderminster Worcestershire, DY11 6RJ, UK
CASE REPORT An 83-year-old man was admitted for investigation of abnormal renal function found on routine testing at a pre-operative surgical assessment clinic. His planned left inguinal hernia repair was temporarily cancelled. Apart from some dif®culty with initiating micturition, he had no other urinary symptoms. Ultrasound (US) demonstrated a marked left hydronephrosis with a thin renal cortex but no cause for the obstruction, and a normal right kidney and bladder. An enhanced CT examination was performed to identify the cause of the hydronephrosis with delayed image at 2 h. This showed a dilated ureter that could be followed down into the pelvis to enter the hernial sac. The ureter then doubled back on itself to re-enter the pelvis and was compressed within the inguinal ring (Fig. 1a). A spiral 3D reconstruction con®rmed this (Fig. 1b). Involvement of the ureter in an inguinal hernia is rare [2,3]. This condition is usually found intra-operatively in elderly male patients without urinary symptoms [3]. The unexpected ureter is at risk during surgery, but it is not cost effective to investigate all patients with inguinal hernias. If however suspected, contrast enhanced spiral CT with delayed imaging during the excretory phase, can exquisitely demonstrate herniation of the ureter into the inguinal sac. L.R. GELLETT C.A. ROOBOTTOM I. P. WELLS
Derriford Hospital, Plymouth, U.K.
References 1 Bradley AJ, Hughes DG. Inguinal hernia ± an unusual cause of bilateral renal obstruction. Clin Radiol 2000;55:69±70.
CLINICAL RADIOLOGY
ROUTINE THIN SLICE MRI EFFECTIVELY DEMONSTRATES THE LUMBAR PARS INTERARTICULARIS SIR ± We read with interest the technical report published in Clinical Radiology by Udeshi and Reeves [1], and agree that thin section MRI can effectively demonstrate the normal pars. In our study of asymptomatic volunteers we found that 74% of L4 and L5 pars were type I on 3 mm sagittal T1W images [2]. However, 24% of the pars were classi®ed as type II or sclerotic. The addition of a 3D GRE sequence increases the number of pars classi®ed as type I to 92%. The authors state that a type II pars reliably excludes spondylolysis. This is not the case. Although the majority of pars that appear hypointense will be normal due to either partial volume effects or sclerosis, it is our experience that some spondylolytic defects (both complete and incomplete) will present with a single discrete hypointense band across the pars. There is no evidence to indicate that this appearance can be reliably distinguished from partial volume or sclerosis. Indeed, in the paper by Saifuddin and Burnett [3], four cases showed this appearance, two with a defect and two without. Further clinical studies with CT correlation are required to fully evaluate this appearance of the pars. When speci®c imaging of the pars is required, MRI should ideally demonstrate a type I pars to con®dently exclude a lysis. In our study [2], 92% of pars were graded type I by inclusion of a sagittal 3D GRE sequence, a ®gure which is repeated in an ongoing clinical study. The 3D sequence also allows the user to perform reconstructed reverse angle views if necessary, which is particularly helpful in the upper lumbar spine where we found sagittal images to be less useful. Reverse angled images may also be helpful in excluding fractures elsewhere in the posterior elements such as laminar fractures. The authors also point out that T2W sequences can demonstrate a type I pars. We utilise T2W images to assess for the presence or absence of marrow oedema in acute defects, in which case fat suppression or STIR imaging is preferable. R.S.D. CAMPBELL A.J. GRAINGER
Department of Radiology South Cleveland Hospital Marton Road Middlesbrough TS4 3BW, UK
para 2) and classi®ed such appearances as type 4 (pars defect) rather than types 1 or 2. We can therefore state that in the remaining pars classi®ed as types 1 and 2 spondylolysis is reliably excluded. Our study did not attempt to assess the ef®cacy of MRI for the diagnosis of spondylolysis but only for con®rmation of the normal pars interarticularis in a group of patients not expected to have spondylolyses (by exclusion of such patients by study design). We therefore cannot comment further regarding additional sequences carried out to establish this diagnosis in borderline cases. Our study was an attempt to demonstrate the reliability of a routine lumbar spine MR imaging sequence for the demonstration of the normal pars interarticularis. We remain convinced that thin slice sagittal T1 and T2 weighted images are effective in this aim. U.L. UDESHI D. REEVES
References 1 Udeshi UL, Reeves D. Routine thin slice MRI effectively demonstrates the lumbar pars interarticularis. Clin Radiol 1999;54:615±619. 2 Campbell RSD, Grainger AJ. Optimization of MRI pulse sequences to visualise the normal pars interarticularis. Clin Radiol 1999;54:63±68. 3 Saifuddin A, Burnett SJD. The value of lumbar spine MRI in the assessment of the pars interarticularis. Clin Radiol 1997;52:666±671.
INGUINAL HERNIA ± AN UNUSUAL CAUSE OF BILATERAL RENAL OBSTRUCTION SIR ± We read with interest the article by Bradley et al. [1] describing a case of bilateral hydronephrosis caused by ileal conduit involvement in a right inguinal hernia. We have recently seen a similar case diagnosed using spiral computed tomography (CT) with 3D reconstruction. On this occasion there had been no previous surgery.
References 1 Udeshi UL, Reeves D. Routine thin slice MRI effectively demonstrates the lumbar pars interarticularis. Clin Radiol 1999;54:615±619. 2 Campbell RSD, Grainger AJ. Optimization of MRI pulse sequences to visualise the normal pars interarticularis. Clin Radiol 1999;54:63± 68. 3 Saifuddin A, Burnett SJD. The value of lumbar spine MRI in the assessment of the pars interarticularis. Clin Radiol 1997;52:666±671.
A REPLY SIR ± We thank Drs Campbell and Grainger for their interest in our paper [1]. We have noted the similarity of results in our respective studies [1,2] on T1 weighted imaging of the L4 and L5 pars:
Type 1 Type 2
Udeshi and Reeves [1]
Campbell and Grainger [2]
75% 20%
74% 24%
In the study by Saifuddin and Burnett [3] a small number of pars showed a single discrete hypo-intense band across the pars and had a 50% ®nding of spondylolysis on plain radiographs. For this reason, we modi®ed Saifuddin and Burnett's classi®cation in our study (as stated in our paper ± page 616,
Kidderminster Health Care NHS Trust Bewdley Road Kidderminster Worcestershire, DY11 6RJ, UK
CASE REPORT An 83-year-old man was admitted for investigation of abnormal renal function found on routine testing at a pre-operative surgical assessment clinic. His planned left inguinal hernia repair was temporarily cancelled. Apart from some dif®culty with initiating micturition, he had no other urinary symptoms. Ultrasound (US) demonstrated a marked left hydronephrosis with a thin renal cortex but no cause for the obstruction, and a normal right kidney and bladder. An enhanced CT examination was performed to identify the cause of the hydronephrosis with delayed image at 2 h. This showed a dilated ureter that could be followed down into the pelvis to enter the hernial sac. The ureter then doubled back on itself to re-enter the pelvis and was compressed within the inguinal ring (Fig. 1a). A spiral 3D reconstruction con®rmed this (Fig. 1b). Involvement of the ureter in an inguinal hernia is rare [2,3]. This condition is usually found intra-operatively in elderly male patients without urinary symptoms [3]. The unexpected ureter is at risk during surgery, but it is not cost effective to investigate all patients with inguinal hernias. If however suspected, contrast enhanced spiral CT with delayed imaging during the excretory phase, can exquisitely demonstrate herniation of the ureter into the inguinal sac. L.R. GELLETT C.A. ROOBOTTOM I. P. WELLS
Derriford Hospital, Plymouth, U.K.
References 1 Bradley AJ, Hughes DG. Inguinal hernia ± an unusual cause of bilateral renal obstruction. Clin Radiol 2000;55:69±70.