Clinical Radiology (1990) 42, 102-104
Diaphragmatic (Bochdalek) Hernias Simulating Pulmonary Metastases on Computed Tomography A. P. BROOKS, A. McLEAN and R. H. REZNEK
Department of Diagnostic Radiology, St Bartholomew's Hospital, London Three patients with known primary malignancy and a normal chest radiograph are presented. Computed tomographic scans viewed on 'lung' settings showed a solitary mass lesion simulating a neoplastic mass in the posterior costophrenic recess in each patient. These lesions in fact were small herniations of abdominal fat into the chest through diaphragmatic defects. Brooks, A.P.,
McLean, A. & Reznek, R.H. (1990). Clinical Radiology 42, 102 104. Diaphragmatic (Bochdalek) Hernias Simulating Pulmonary Metastases on Computed Tomography
Computed tomography (CT) is more sensitive than plain chest radiography for the detection of small pulmonary nodules, especially those in the peripheral portions of the lungs, or in the posterior costophrenic recesses (Jost et al., 1978; Schaner et al., 1978). These are also the most common sites of development of pulmonary metastases (Crow et al., 1981). CT is therefore widely used to evaluate patients with suspected pulmonary metastases when plain chest radiographs are normal. One pitfall in the diagnosis of metastatic disease is the interpretation of uncalcified granulomata as neoplastic lesions (Schaner et al., 1978). We present three patients with known primary malignant disease in whom a small asymptomatic Bochdalek hernia might have been misinterpreted as a solitary basal lung metastasis: a potential pitfall of CT interpretation which we do not believe has been emphasized previously.
(b)
CASE R E P O R T S Case 1. A 60-year-old m a n with a primary rectal carcinoma, was found to have a solitary liver metastasis on ultrasound. A chest radiograph had shown no significant abnormality. Chest CT was performed to exclude pulmonary metastases prior to surgery to remove the liver lesion. When viewed on 'lung' settings, a well-defined mass was identified in the left costophrenic recess (Fig. la). Subsequent evaluation
(c) Fig. 1 - Case 1. (a) Well-defined mass (arrows) in the left costophrenic recess medially at L 750 W 1000. (b) At L + 40 W 650, the mass is of fat attenuation. (c) 1.5 cm inferior to (b) continuity o f fat attenuation through the diaphragmatic defect (arrow) is demonstrated.
(a) Correspondence to: Dr A. P. Brooks, Department of Diagnostic Radiology, St Bartholomew's Hospital, West Smithfield, London EC1A 7BE.
on 'soft tissue' settings revealed that the mass was of fat attenuation, and communicated through a diaphragmatic defect with intra-abdominal f a t ( F i g , lb, c). The lesion was thus shown to be a diaphragmatic herniation and not a solitary metastasis. Partial hepatectomy was therefore performed.
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(~)
(a)
(b) (b) Fig. 3 Case 3. (a) Well-defined lesion (arrow) adjacent to the diaphragm at L --750 W 500. (b) At L +40 W 650 the mass is clearly of fat attenuation, and a narrow diaphragmatic defect is seen (arrow).
Case 3. A 63-year-old woman had a malignant fibrous histiocytoma of the thigh. A chest radiograph was normal. Staging chest CT was performed to exclude pulmonary metastases prior to treatment. The only suggestion of a metastatic lesion was a well-defined mass closely related to the right hemidiaphragm, Which proved to represent a hernia through a very narrow diaphragmatic defect (Fig. 3). The primary tumour was therefore treated by excision and local radiotherapy.
(c) Fig. 2 - Case 2. (a) Irregular mass (arrows) at the left base at L -- 750 W 1000. (b) Predominantly fat attenuation of the mass is evident at L + 40 W 650. (c) 1 cm inferior to (b) continuity through a wide diaphragmatic defect is seen.
Case 2. A 67-year-old man with a history of previous right breast carcinoma, treated by surgery and radiotherapy, had a CT performed to assess possible local chest wall recurrence. A chest radiograph had been interpreted as normal. On 'lung' settings, a somewhat irregular mass was apparent at the left base on chest CT (Fig. 2a). Further evaluation revealed that the lesion represented fatty tissue which had herniated through a relatively wide diaphragmatic defect (Fig. 2b, c). The chest Wall changes were considered to be due to previous radiotherapy, and further treatment was therefore withheld.
DISCUSSION I n m o s t cases, t h e d i a g n o s i s o f a B o c h d a l e k h e r n i a o n C T is s t r a i g h t f o r w a r d , e s p e c i a l l y w h e r e C T is p e r f o r m e d to e v a l u a t e a lesion visible o n a c h e s t r a d i o g r a p h . T h e t y p i c a l C T f e a t u r e s are: (a) a m a s s a b u t t i n g the u p p e r s u r f a c e o f the d i a p h r a g m , u s u a l l y o f fat a t t e n u a t i o n b u t o c c a s i o n a l l y o f soft tissue a t t e n u a t i o n ; (b) a c h a r a c t e r i s t i c l o c a t i o n o n the p o s t e r o m e d i a l a s p e c t o f the h e m i d i a p h r a g m ; (c) d i s c o n t i n u i t y o f t h e d i a p h r a g m a d j a c e n t to t h e m a s s ; a n d (d) c o n t i n u i t y o f t h e densities a b o v e a n d b e l o w the d i a p h r a g m t h r o u g h t h e d i a p h r a g m a t i c d e f e c t ( D e M a r t i n i a n d H o u s e , 1980; G a l e , 1985; S h i n et al., 1987). T h e f e a t u r e s (c) a n d (d) d i f f e r e n t i a t e these h e r n i a s f r o m d i a p h r a g m a t i c l i p o m a s ( G a l e , 1985; S h i n et al., 1987). T h e y w e r e c o n s i d e r e d r e l a t i v e l y r a r e in a d u l t s u n t i l
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a study revealed that they were present on CT in 6% of 940 patients (Gale, 1985). Small hernias, however, may be misinterpreted as lung nodules if CT is specifically directed towards identifying such lesions, for example 'routine' screening chest CT in patients with malignant disease. All of our patients had a known primary malignancy, and a normal chest radiograph. In this situation, the finding of even a single pulmonary metastasis may have a dramatic bearing on subsequent management. W h i l e metastases are usually multiple, solitary deposits do occur, especially from primary carcinoma of the colon, kidney, testis or breast, or with malignant melanoma or sarcomas (Pare and Fraser, 1983). A recent age-stratified study of the CT appearances of the diaphragm has cast doubt on whether all such diaphragmatic defects and hernias identified in adults are developmental (Caskey et al., 1989). No such abnormalities were identified in patients below 40 years of age, suggesting that they are in fact acquired. However, for simplicity, we have referred to these abnormalities as Bochdalek hernias. Any lesion identified in the inferomedial aspect of the posterior costophrenic recess on CT at 'lung' settings must be evaluated carefully in order to prevent misinterpretation. Especially if the lesion abuts the diaphragm, the possibility of an extrapulmonary lesion must be considered. Viewing at other window levels and widths is essential to establish whether the lesion is of soft tissue, calcium or fat attenuation (with slices being obtained with
narrow collimation to reduce partial volume averaging, if necessary). The identification of a solitary lesion in this region, especially if it is of fat attenuation, should also p r o m p t a search for an associated diaphragmatic defect in order to establish the diagnosis of a Bochdalek hernia. Although lesions in this situation can be biopsied percuta. neously (De Martini and House, 1980), such an invasive procedure is best avoided if possible.
REFERENCES
Caskey, CI, Zerhouni, EA, Fishman, EK & Rahmouni, AD (1989). Aging of the diaphragm: a CT study. Radiology, 171, 385-389. Crow, J, Slavin, G & Kreel, L (1981). Pulmonary metastasis: a pathologic and radiologic study. Cancer, 47, 2595-2602. De Martini, WJ & House, AJS (1980). Partial Bochdalek's herniation. Computerized tomographic evaluation. Chest, 77, 702-704. Gale, ME (1985). Bochdalek hernia: prevalenceand CT characteristics Radiology, 156, 449-452. Jost, RG, Sagel, SS, Stanley, RJ & Levitt, RG (1978). Computed tomography of the thorax. Radiology, 126, 125-136. Pare, JAP & Fraser, RG (1983). Synopsis of Diseases of the Chest, p. 445. W. B. Saunders, Philadelphia. Schaner, EG, Chang, AE, Doppman, JL, Conkle, DM, Flye, MW & Rosenberg, SA (1978). Comparison of computed and conventional whole-lung tomography in detecting pulmonary nodules: a prospective radiologic-pathologic study. American Journal of Roentgenology, 131, 51 54. Shin, MS, Mulligan, SA, Baxley, WA & Ho, K-J (1987). Bochdalek hernia of diaphragm in the adult, diagnosis by computed tomography. Chest, 92, 1098 1101.
Diaphragmatic (Bochdalek) Hernias Simulating Pulmonary Metastases on Computed Tomography A. P. BROOKS, A. McLEAN and R. H. REZNEK
Department of Diagnostic Radiology, St Bartholomew's Hospital, London Three patients with known primary malignancy and a normal chest radiograph are presented. Computed tomographic scans viewed on 'lung' settings showed a solitary mass lesion simulating a neoplastic mass in the posterior costophrenic recess in each patient. These lesions in fact were small herniations of abdominal fat into the chest through diaphragmatic defects. Brooks, A.P.,
McLean, A. & Reznek, R.H. (1990). Clinical Radiology 42, 102 104. Diaphragmatic (Bochdalek) Hernias Simulating Pulmonary Metastases on Computed Tomography
Computed tomography (CT) is more sensitive than plain chest radiography for the detection of small pulmonary nodules, especially those in the peripheral portions of the lungs, or in the posterior costophrenic recesses (Jost et al., 1978; Schaner et al., 1978). These are also the most common sites of development of pulmonary metastases (Crow et al., 1981). CT is therefore widely used to evaluate patients with suspected pulmonary metastases when plain chest radiographs are normal. One pitfall in the diagnosis of metastatic disease is the interpretation of uncalcified granulomata as neoplastic lesions (Schaner et al., 1978). We present three patients with known primary malignant disease in whom a small asymptomatic Bochdalek hernia might have been misinterpreted as a solitary basal lung metastasis: a potential pitfall of CT interpretation which we do not believe has been emphasized previously.
(b)
CASE R E P O R T S Case 1. A 60-year-old m a n with a primary rectal carcinoma, was found to have a solitary liver metastasis on ultrasound. A chest radiograph had shown no significant abnormality. Chest CT was performed to exclude pulmonary metastases prior to surgery to remove the liver lesion. When viewed on 'lung' settings, a well-defined mass was identified in the left costophrenic recess (Fig. la). Subsequent evaluation
(c) Fig. 1 - Case 1. (a) Well-defined mass (arrows) in the left costophrenic recess medially at L 750 W 1000. (b) At L + 40 W 650, the mass is of fat attenuation. (c) 1.5 cm inferior to (b) continuity o f fat attenuation through the diaphragmatic defect (arrow) is demonstrated.
(a) Correspondence to: Dr A. P. Brooks, Department of Diagnostic Radiology, St Bartholomew's Hospital, West Smithfield, London EC1A 7BE.
on 'soft tissue' settings revealed that the mass was of fat attenuation, and communicated through a diaphragmatic defect with intra-abdominal f a t ( F i g , lb, c). The lesion was thus shown to be a diaphragmatic herniation and not a solitary metastasis. Partial hepatectomy was therefore performed.
103
D I A P H R A G M A T I C HERNIA ON CT
(~)
(a)
(b) (b) Fig. 3 Case 3. (a) Well-defined lesion (arrow) adjacent to the diaphragm at L --750 W 500. (b) At L +40 W 650 the mass is clearly of fat attenuation, and a narrow diaphragmatic defect is seen (arrow).
Case 3. A 63-year-old woman had a malignant fibrous histiocytoma of the thigh. A chest radiograph was normal. Staging chest CT was performed to exclude pulmonary metastases prior to treatment. The only suggestion of a metastatic lesion was a well-defined mass closely related to the right hemidiaphragm, Which proved to represent a hernia through a very narrow diaphragmatic defect (Fig. 3). The primary tumour was therefore treated by excision and local radiotherapy.
(c) Fig. 2 - Case 2. (a) Irregular mass (arrows) at the left base at L -- 750 W 1000. (b) Predominantly fat attenuation of the mass is evident at L + 40 W 650. (c) 1 cm inferior to (b) continuity through a wide diaphragmatic defect is seen.
Case 2. A 67-year-old man with a history of previous right breast carcinoma, treated by surgery and radiotherapy, had a CT performed to assess possible local chest wall recurrence. A chest radiograph had been interpreted as normal. On 'lung' settings, a somewhat irregular mass was apparent at the left base on chest CT (Fig. 2a). Further evaluation revealed that the lesion represented fatty tissue which had herniated through a relatively wide diaphragmatic defect (Fig. 2b, c). The chest Wall changes were considered to be due to previous radiotherapy, and further treatment was therefore withheld.
DISCUSSION I n m o s t cases, t h e d i a g n o s i s o f a B o c h d a l e k h e r n i a o n C T is s t r a i g h t f o r w a r d , e s p e c i a l l y w h e r e C T is p e r f o r m e d to e v a l u a t e a lesion visible o n a c h e s t r a d i o g r a p h . T h e t y p i c a l C T f e a t u r e s are: (a) a m a s s a b u t t i n g the u p p e r s u r f a c e o f the d i a p h r a g m , u s u a l l y o f fat a t t e n u a t i o n b u t o c c a s i o n a l l y o f soft tissue a t t e n u a t i o n ; (b) a c h a r a c t e r i s t i c l o c a t i o n o n the p o s t e r o m e d i a l a s p e c t o f the h e m i d i a p h r a g m ; (c) d i s c o n t i n u i t y o f t h e d i a p h r a g m a d j a c e n t to t h e m a s s ; a n d (d) c o n t i n u i t y o f t h e densities a b o v e a n d b e l o w the d i a p h r a g m t h r o u g h t h e d i a p h r a g m a t i c d e f e c t ( D e M a r t i n i a n d H o u s e , 1980; G a l e , 1985; S h i n et al., 1987). T h e f e a t u r e s (c) a n d (d) d i f f e r e n t i a t e these h e r n i a s f r o m d i a p h r a g m a t i c l i p o m a s ( G a l e , 1985; S h i n et al., 1987). T h e y w e r e c o n s i d e r e d r e l a t i v e l y r a r e in a d u l t s u n t i l
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a study revealed that they were present on CT in 6% of 940 patients (Gale, 1985). Small hernias, however, may be misinterpreted as lung nodules if CT is specifically directed towards identifying such lesions, for example 'routine' screening chest CT in patients with malignant disease. All of our patients had a known primary malignancy, and a normal chest radiograph. In this situation, the finding of even a single pulmonary metastasis may have a dramatic bearing on subsequent management. W h i l e metastases are usually multiple, solitary deposits do occur, especially from primary carcinoma of the colon, kidney, testis or breast, or with malignant melanoma or sarcomas (Pare and Fraser, 1983). A recent age-stratified study of the CT appearances of the diaphragm has cast doubt on whether all such diaphragmatic defects and hernias identified in adults are developmental (Caskey et al., 1989). No such abnormalities were identified in patients below 40 years of age, suggesting that they are in fact acquired. However, for simplicity, we have referred to these abnormalities as Bochdalek hernias. Any lesion identified in the inferomedial aspect of the posterior costophrenic recess on CT at 'lung' settings must be evaluated carefully in order to prevent misinterpretation. Especially if the lesion abuts the diaphragm, the possibility of an extrapulmonary lesion must be considered. Viewing at other window levels and widths is essential to establish whether the lesion is of soft tissue, calcium or fat attenuation (with slices being obtained with
narrow collimation to reduce partial volume averaging, if necessary). The identification of a solitary lesion in this region, especially if it is of fat attenuation, should also p r o m p t a search for an associated diaphragmatic defect in order to establish the diagnosis of a Bochdalek hernia. Although lesions in this situation can be biopsied percuta. neously (De Martini and House, 1980), such an invasive procedure is best avoided if possible.
REFERENCES
Caskey, CI, Zerhouni, EA, Fishman, EK & Rahmouni, AD (1989). Aging of the diaphragm: a CT study. Radiology, 171, 385-389. Crow, J, Slavin, G & Kreel, L (1981). Pulmonary metastasis: a pathologic and radiologic study. Cancer, 47, 2595-2602. De Martini, WJ & House, AJS (1980). Partial Bochdalek's herniation. Computerized tomographic evaluation. Chest, 77, 702-704. Gale, ME (1985). Bochdalek hernia: prevalenceand CT characteristics Radiology, 156, 449-452. Jost, RG, Sagel, SS, Stanley, RJ & Levitt, RG (1978). Computed tomography of the thorax. Radiology, 126, 125-136. Pare, JAP & Fraser, RG (1983). Synopsis of Diseases of the Chest, p. 445. W. B. Saunders, Philadelphia. Schaner, EG, Chang, AE, Doppman, JL, Conkle, DM, Flye, MW & Rosenberg, SA (1978). Comparison of computed and conventional whole-lung tomography in detecting pulmonary nodules: a prospective radiologic-pathologic study. American Journal of Roentgenology, 131, 51 54. Shin, MS, Mulligan, SA, Baxley, WA & Ho, K-J (1987). Bochdalek hernia of diaphragm in the adult, diagnosis by computed tomography. Chest, 92, 1098 1101.
