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Aberrant thymus: A misleading mediastinal mass
Aberrant Thymus: A Misleading Mediastinal Mass By P.S. Malone and R.J. Fitzgerald Dublin, Ireland 9 W e report t w o cases in which aberrant thymic tissue caused a misleading superior mediastinal mass. The diagnosis can be made by awareness of it and by use of appropriate investigations. Should surgery be performed w e recommend frozen section biopsy if ectopic thymus is suspected, and if confirmed, the mass should not be excised unless it is causing serious mechanical problems. 9 1 9 8 7 by Grune & S t r a t t o n , Inc.
in the left mediastinum. Further dissection demonstrated a normal thymus anterior to the aortic arch, but there was no obvious communication between the thymus and the mass. There was no evidence of tracheal compression but as the nature of the mass was unclear it was completely excised. Histology revealed normal thymic tissue. Postoperative chest x-rays showed a persistent normal thymic shadow (Fig 3). The patient made an uneventful recovery and repeated immunologic investigations were normal.
INDEX W O R D S : Ectopic thymus.
Case 2
H O U G H U N C O M M O N , aberrations in migration of thymic tissue can occur, and there are descriptions of thymic tissue in situations as varied as the base of the skull, and the mediastinum at the tracheal bifurcation. Cervical ectopia would appear to be the most common site. 1There are only sporadic case reports of aberrant thymus causing superior mediastinal masses. 2~ Dunbar 5 emphasized the rarity with which aberrant thymus produces symptoms by compressing adjacent structures and the importance of differentiating it from other pathologic lesions in the mediastinum. We have recently encountered two cases of superior mediastinal masses caused by aberrantly positioned thymus and the purpose of this paper is to highlight the condition and describe our management.
T
CASE REPORTS
Case 2 was a male who presented at 6 weeks of age with a history of apnoeic episodes and respiratory tract infection. Chest roentgenog r a m demonstrated a soft tissue opacity in the right superior mediastinum, which was initially diagnosed as upper lobe atelectesis. However, there were further episodes of respiratory infection and the opacity remained unchanged on roentgenogram. Its appearance was similar to that demonstrated in Fig 1. Ultrasonography demonstrated a solid mass which was echogenically consistent with thymic tissue. A barium swallow revealed that the esophagus was deviated to the left and a C A T scan demonstrated a similar pattern and relationship to that described in case 1. All other investigations were normal. Based on our previous experience, a policy of conservative treatment and observation was advised. However, due to parental anxiety we proceeded to thoracotomy and frozen section biopsy. This revealed normal thymic tissue and the mass was not excised. The patient is well 3 months postoperatively.
DISCUSSION The position of the aberrant
thymic
t i s s u e in t h e s e
t w o c a s e s is s i m i l a r t o t h o s e p r e v i o u s l y d e s c r i b e d . 2-4 I t
Case 1 Case 1 was a male who developed mild respiratory difficulties immediately following a normal delivery. These resolved over a two-day period following which there was no recurrence of symptoms. However, a chest x-ray demonstrated a soft tissue opacity in the right superior mediastinum which remained unchanged on subsequent radiographs (Fig 1). A normal thymic shadow was seen on all roentgenograms. Ultrasonography demonstrated a solid mass, measuring 3 • 3 cm, lying posterior to the aortic arch and a barium swallow showed that it was closely related to the esophagus deviating it to the left. Computerized axial tomography (CAT scan) confirmed the mass to be solid lying adjacent to the trachea and passing posterior to it (Fig 2). Urinary V M A was normal but as the mass was regarded as being pathologic, surgery was performed. At thoracotomy a smooth mass was found lying posterolateral to the superior vena cava and passing medially between the trachea and esophagus ending closely applied to the posterior aspect of the aorta
From the Children's Research Centre, Our Lady's Hospital for Sick Children, Crumlin, Dublin, Ireland. Address reprint requests to Mr R.J. Fitzgerald, Children's Research Centre, Our Lady's Hospital for Sick Children, Crumlin, Dublin 12, Ireland. 9 1987 by Grune & Stratton, Inc. 0022-3468/87/2202-0009503.00/0 130
Fig 1. Chest roentgenogram showing the right superior mediastinal mass. Journal of Pediatric Surgery, Vo122, No 2 (February), 1987: pp 130-131
ABERRANT THYMUS: A MISLEADING MEDIASTINAL MASS
Fig 2.
131
Fig 3. Postoperative chest roentgenogram showing a normal thymic shadow.
C A T scan with the arrow illustrating the mass.
lay posterolateral to the superior vena cava, wrapping posteriorly around the trachea to end lying posterior to the aortic arch. W e do not believe it contributed to the respiratory symptoms in either of our two cases, and the prinicpal problems we encountered were in distinguishing the masses from pathologic conditions such as pulmonary atelectesis or consolidation, t h y m o m a , bronchogenic cyst, and neuroblastoma. This problem is highlighted by our aggressive m a n a g e m e n t of the first case. The most c o m m o n presentation of aberrant mediastinal thymus is the incidental finding of a right-sided superior mediastinal mass on chest roentgenogram. Ultrasonography is a potentially useful investigation when such masses are of uncertain origin. Following our experience in the first case, we were able to interpret the ultrasound findings as showing an echogenic pattern consistent with normal thymic tissue. C A T scan is also helpful as this demonstrates the
relationships of the mass, which are relatively constant for aberrantly positioned mediastinal thymus as previously described in the literature. 24 T h o u g h D u n b a r 5 claims that normal thymic tissue does not cause deviation of related structures, in both our cases the esophagus was deviated to the left. Therefore, we do not regard this as a reason to exclude the diagnosis. Awareness of the condition and the proper use of the previously mentioned investigations enables a confident diagnosis of aberrant thymic tissue in the right superior mediastinum to be made. This is illustrated by our m a n a g e m e n t of the second case where we considered observation to be justifiable and surgery was performed only on the insistance of the parents. If surgery is undertaken, we recommend frozen section biopsy as the discovery of normal thymic tissue will avoid a potentially hazardous dissection. Excision of aberrant thymus is only indicated for those rare cases where there is evidence of airway obstruction.
REFERENCES
1. Finch DRA, Gough MH: Ectopic thymic tissue presenting as a lateral cervical swelling. Br J Surg 59:885-886, 1972 2. Sealy WC, Weaver WL, Young WG: Severe airway obstruction in infancy due to the thymus gland. Ann Thorac Surg 1:389402, 1965 3. Shackelford GD, McAlister WH: The aberrantly positioned
thymus. A cause of mediastinal or neck masses in children. Am J Roentgenol 120:291-296, 1974 4. Noback GJ: A contribution to the topographic anatomy of the thymus gland, with particular reference to its changes at birth and in the period of the new-born. Am J Dis Child 22:120-144, 1921 5. Dunbar JS: Upper respiratory tract obstruction in infants and children. Am J Roentgen 109:227-246, 1970
in the left mediastinum. Further dissection demonstrated a normal thymus anterior to the aortic arch, but there was no obvious communication between the thymus and the mass. There was no evidence of tracheal compression but as the nature of the mass was unclear it was completely excised. Histology revealed normal thymic tissue. Postoperative chest x-rays showed a persistent normal thymic shadow (Fig 3). The patient made an uneventful recovery and repeated immunologic investigations were normal.
INDEX W O R D S : Ectopic thymus.
Case 2
H O U G H U N C O M M O N , aberrations in migration of thymic tissue can occur, and there are descriptions of thymic tissue in situations as varied as the base of the skull, and the mediastinum at the tracheal bifurcation. Cervical ectopia would appear to be the most common site. 1There are only sporadic case reports of aberrant thymus causing superior mediastinal masses. 2~ Dunbar 5 emphasized the rarity with which aberrant thymus produces symptoms by compressing adjacent structures and the importance of differentiating it from other pathologic lesions in the mediastinum. We have recently encountered two cases of superior mediastinal masses caused by aberrantly positioned thymus and the purpose of this paper is to highlight the condition and describe our management.
T
CASE REPORTS
Case 2 was a male who presented at 6 weeks of age with a history of apnoeic episodes and respiratory tract infection. Chest roentgenog r a m demonstrated a soft tissue opacity in the right superior mediastinum, which was initially diagnosed as upper lobe atelectesis. However, there were further episodes of respiratory infection and the opacity remained unchanged on roentgenogram. Its appearance was similar to that demonstrated in Fig 1. Ultrasonography demonstrated a solid mass which was echogenically consistent with thymic tissue. A barium swallow revealed that the esophagus was deviated to the left and a C A T scan demonstrated a similar pattern and relationship to that described in case 1. All other investigations were normal. Based on our previous experience, a policy of conservative treatment and observation was advised. However, due to parental anxiety we proceeded to thoracotomy and frozen section biopsy. This revealed normal thymic tissue and the mass was not excised. The patient is well 3 months postoperatively.
DISCUSSION The position of the aberrant
thymic
t i s s u e in t h e s e
t w o c a s e s is s i m i l a r t o t h o s e p r e v i o u s l y d e s c r i b e d . 2-4 I t
Case 1 Case 1 was a male who developed mild respiratory difficulties immediately following a normal delivery. These resolved over a two-day period following which there was no recurrence of symptoms. However, a chest x-ray demonstrated a soft tissue opacity in the right superior mediastinum which remained unchanged on subsequent radiographs (Fig 1). A normal thymic shadow was seen on all roentgenograms. Ultrasonography demonstrated a solid mass, measuring 3 • 3 cm, lying posterior to the aortic arch and a barium swallow showed that it was closely related to the esophagus deviating it to the left. Computerized axial tomography (CAT scan) confirmed the mass to be solid lying adjacent to the trachea and passing posterior to it (Fig 2). Urinary V M A was normal but as the mass was regarded as being pathologic, surgery was performed. At thoracotomy a smooth mass was found lying posterolateral to the superior vena cava and passing medially between the trachea and esophagus ending closely applied to the posterior aspect of the aorta
From the Children's Research Centre, Our Lady's Hospital for Sick Children, Crumlin, Dublin, Ireland. Address reprint requests to Mr R.J. Fitzgerald, Children's Research Centre, Our Lady's Hospital for Sick Children, Crumlin, Dublin 12, Ireland. 9 1987 by Grune & Stratton, Inc. 0022-3468/87/2202-0009503.00/0 130
Fig 1. Chest roentgenogram showing the right superior mediastinal mass. Journal of Pediatric Surgery, Vo122, No 2 (February), 1987: pp 130-131
ABERRANT THYMUS: A MISLEADING MEDIASTINAL MASS
Fig 2.
131
Fig 3. Postoperative chest roentgenogram showing a normal thymic shadow.
C A T scan with the arrow illustrating the mass.
lay posterolateral to the superior vena cava, wrapping posteriorly around the trachea to end lying posterior to the aortic arch. W e do not believe it contributed to the respiratory symptoms in either of our two cases, and the prinicpal problems we encountered were in distinguishing the masses from pathologic conditions such as pulmonary atelectesis or consolidation, t h y m o m a , bronchogenic cyst, and neuroblastoma. This problem is highlighted by our aggressive m a n a g e m e n t of the first case. The most c o m m o n presentation of aberrant mediastinal thymus is the incidental finding of a right-sided superior mediastinal mass on chest roentgenogram. Ultrasonography is a potentially useful investigation when such masses are of uncertain origin. Following our experience in the first case, we were able to interpret the ultrasound findings as showing an echogenic pattern consistent with normal thymic tissue. C A T scan is also helpful as this demonstrates the
relationships of the mass, which are relatively constant for aberrantly positioned mediastinal thymus as previously described in the literature. 24 T h o u g h D u n b a r 5 claims that normal thymic tissue does not cause deviation of related structures, in both our cases the esophagus was deviated to the left. Therefore, we do not regard this as a reason to exclude the diagnosis. Awareness of the condition and the proper use of the previously mentioned investigations enables a confident diagnosis of aberrant thymic tissue in the right superior mediastinum to be made. This is illustrated by our m a n a g e m e n t of the second case where we considered observation to be justifiable and surgery was performed only on the insistance of the parents. If surgery is undertaken, we recommend frozen section biopsy as the discovery of normal thymic tissue will avoid a potentially hazardous dissection. Excision of aberrant thymus is only indicated for those rare cases where there is evidence of airway obstruction.
REFERENCES
1. Finch DRA, Gough MH: Ectopic thymic tissue presenting as a lateral cervical swelling. Br J Surg 59:885-886, 1972 2. Sealy WC, Weaver WL, Young WG: Severe airway obstruction in infancy due to the thymus gland. Ann Thorac Surg 1:389402, 1965 3. Shackelford GD, McAlister WH: The aberrantly positioned
thymus. A cause of mediastinal or neck masses in children. Am J Roentgenol 120:291-296, 1974 4. Noback GJ: A contribution to the topographic anatomy of the thymus gland, with particular reference to its changes at birth and in the period of the new-born. Am J Dis Child 22:120-144, 1921 5. Dunbar JS: Upper respiratory tract obstruction in infants and children. Am J Roentgen 109:227-246, 1970