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Respiratory complications in cervical thymic cysts
Respiratory Complications in Cervical Thymic Cysts By Charles W. Wagner, Charles D. Vinocur, William H. Weintraub, and E. Stevers Golladay Little Rock, Arkansas and Philadelphia, Pennsylvania 9 Thymic cysts are considered uncommon lesions in the differential diagnosis of pediatric neck masses. They have been described as asymptomatic and of little clinical consequence. Recent reports have stressed the possibility of respiratory compromise associated with these lesions. W e reviewed our experience with cervical thymic cysts with emphasis on respiratory problems. Ten pediatric patients underwent surgery and were found to have cervical thymic cysts. Ages ranged from newborn to 14 years. There w e r e four boys and six girls. Two were found to have the thymic cysts at time of neck exploration for Grave's disease and hyperparathyroidism. Of the remaining eight patients, all had mobile cystic masses, located anterior to but extending beneath the lower third of the sternocleidomastoid muscle. The size of the mass ranged from 3.0 to 8.5 cm. Preoperative diagnosis included cystic hygroma/branchial cleft cyst (five), lymphoma (one), teratorna (one), and thymic cyst (one). All had a history of rapidly developing neck mass. Seven of the eight gave a history of upper respiratory tract infection (URI} prior to the development of the mass. Five had imaging studies that showed tracheal compression. Three of these required airway management in the early postoperative period. All w e r e excised through a neck incision, with two requiring sternal extension. Histology showed cholesterol crystals, Hassall's corpuscles, and giant cell reaction diagnosis of thymic cysts. There has been no recurrence and no permanent respiratory sequela in the ten patients. Cervical thymic cysts are benign lesions that may be more common than literature suggests. This diagnosis should be entertained with neck masses that are located anterior to but with extension below the lower third of the sternocleidomastoid muscle. Respiratory compromise can indeed occur in these patients, especially with preoperative studies that demonstrate tracheal compression. In those children with tracheal compression, close postoperative respiratory monitoring is essential. 9 1988 by Grune R, Stratton, Inc. INDEX WORDS: Thymic cyst; thymic duct remnant cyst.
rHILE THE ORIGIN of thymic cysts has long
W been recognized, they have been considered uncommon lesions in the diagnosis of pediatric neck masses and (except for diagnosis) have been without clinical importance. Of the 75 cysts reported in patients <20 years of age, all were described as asymptomatic and few associated with respiratory embarrassment. ~s Since 1963 at St. Christopher's Hospital for Children and Arkansas Children's Hospital, ten patients underwent surgery involving removal of cervical thymic cyst. These patients are reviewed with special emphasis on three in whom respiratory problems developed.
Journal of PediatricSurgery, Vol 23, No 7 (July), 1988: pp 657-660
MATERIALS AND METHODS There were ten children ranging in age from newborn to 14 years who underwent subsequent removal of thymic cysts from the neck. Four of these occurred in boys and six occurred in girls. Two underwent neck exploration; one for Grave's disease and the other for hyperparathyroidism, and were found to have an associated thymic cyst with the primary disease. The remaining eight were operated on for a cystic neck mass (Table 1). Seven of eight had 2 URI within 2 weeks prior to presentation. This coincided with the rapid increase in mass size. None had any symptoms of neuromuscular disorders in their medical history. All eight had a mobile cystic mass located anterior to but extending beneath the lower third of the sternocleidomastoid muscle. The size of the mass ranged from 3.0 to 8.5 cm at its largest diameter. None of the patients was noted to have any abnormal hematologic studies prior to surgery. Preperative diagnosis includes cystic hygroma/branchial cleft cyst (five), lymphoma (one), teratoma (one), and thymic cyst (one). Tracheal and/or esophageal compression were demonstrated by either barium swallow, neck films, chest x-rays, computerized axial tomography, or ultrasound in five patients. Of this group, one developed severe respiratory problems requiring preoperative intubation and postoperative airway management. Two others required airway management immediately after surgery. All masses were excised through a cervical incision, with two requiring partial sternotomy for mediastinal extension. All specimens were cystic, containing brownish fluid. Histology showed Hassall's corpuscles, giant cell reaction, and cholesterol crystals diagnostic of thymic cyst. Follow-up on all patients ranged from 4 months until discharge at 4 years. During this period there were no recurrences, no residual complications, and no respiratory sequelae.
CASE REPORTS
Case I A 9-year-old black male was evaluated for a mass on the left side of the neck of 1 week's duration. He had a history of recent URI subsequent to the development of the mass. Upon physical examination, the lesion measured 3 x 5 cm, was mobile, and was located on the lower third of the neck, anterior to but extending below the sternocleidomastoid muscle. Chest x-rays indicated the trachea was compressed and deviated. Upon barium swallow, esophageal compression was seen. The patient underwent excision of the lesion through a cervical approach. The lesion was noted to extend into the
From the University of Arkansas for Medical Sciences and Arkansas Children's Hospital, Little Rock; and St. Christopher's Hospital for Children, Philadelphia. Presented at the 36th Annual Meeting of the Surgical Section of the American Academy of Pediatrics, New Orleans, October 31 to November 2, 1987. Address reprint requests tO Charles IV. Wagner, MD, Arkansas Children's Hospital, 800 Marshall St, Little Rock, A R 722023591. 9 1988 by Grune & Stratton, Inc. 0022-3468/88/2307-0015503.00/0
657
658
WAGNER ET AL Table 1. Patients With a Palpable Cervical Mass
Patient No.
Age (yr)/Sex
Size (cm)/URI History
1
11/F
8/+
2
9/M
3.5/+
PROV DX
Location
Cystic hygroma
R
Teratoma
L
3
12/F
4/§
Lymphoma
L
4 5
7/F 4/F
4/+ 4/+
Branchial cleft cyst Cystic hygroma
R R
6 7 8
3 d/M 5/M 4/F
5/-6/+ 8.5/+
Branchial cleft cyst Branchial cleft cyst Thymic cyst
L L L
Radiologic Studies (trachea compression) Neck films, BA swallow CXR, BA swallow CXR, ultrasound ND CXR, neck films, BA swallow, CT, ultrasound
Neck ND Ultrasound
Recurrence/ Follow-up + +
No/2 yr
+
No~3 yr
+ + +
No/4 yr
+ 33333-
No/3 yr No/1 yr
No/3 yr No/4 mo No/6 mo
Abbreviations: PROV DX, provisional diagnosis; BA, barium; CXR, chest x-ray; ND, not done.
mediastinum and a sternotomy was performed to aid in total resection. Twelve hours postoperatively,he developed severe stridor and respiratory distress. There was no sign of hematoma or external compression, but to relieve the distress, a tracheostomy was performed. The respiratory distress quickly resolved and the child underwent decannulation in 1 month without difficulty.At 3 years follow-up, he showed no recurrence and no respiratory problems.
Case 2 A 4-year-old black female had a 2-week history of an enlarging mass on the right side of the neck and dysphagia. She had a history of previousURI. Upon physical examination the mass was 3 • 4 cm, mobile, and located at the lower third of the neck, anterior to but extending below the sternocleidomastoidmuscle. Tracheal compression was demonstrated on lateral neck films,deviationof the cervical esophagus on barium swallow, and tracheal compression on computerized tomography (CT) scan (Fig 1). During preoperative evaluation, the cyst doubled in size. Excision was accomplished through a cervical approach with a partial sternotomy. In the early postoperative course, she developed stridor and subsequent right upper lobe, and total left lung atelectasis. She underwent laryngoscopy and bronchoscopy,and was noted to have tracheal narrowing. She required intubation for 72 hours and vigorous pulmonary care for 3 weeks in order to resolveher respiratory problem.At 1 year she showed no signs of recurrence or respiratory problems. The followup CT scan showed a normal trachea.
Fig 1. CT scan of lower cervical region shows a right cyst mass compression and deviation of trachea.
Case 3 Upon physical examination, a newborn boy was noted to have a mass in the left cervical region. Forty-eight hours after birth the mass rapidly enlarged. The patient developed respiratory problems and required intubation. He underwent excision of this through a cervical approach. The mass showed signs of hemorrhage into the cyst. Postoperatively he was extubated within 48 hours of surgery. Two years after surgery he had no respiratory problems and no signs of recurrence. DISCUSSION I n 190 l, Pollosson and Piery m a d e the first a t t e m p t at surgical excision of this lesion in a n i n f a n t .9 T h e first successful excision in a child was performed by Hyde et al in 1944.1~ Cases have been sporadic, a n d to date, 75 have occurred in children < 2 0 years. W i t h the addition of these ten cases, over 70% of cervical thymic cysts are in patients < 2 0 years of age. Johnsen and Br~tlau ll have suggested that the prevalence in childhood m a y be due to the fact that the t h y m u s undergoes its greatest development in the p r e p u b e r t y period. Barrick a n d O'Kel112 state further that the thymus reaches its greatest relative size from age 2 to 4, with its greatest absolute size at puberty. W i t h regard to embryology, the t h y m u s originates from the third branchial pouch bilaterally in the 6th week of development. D u r i n g weeks 7 a n d 8, the t h y m u s elongates and descends to the level of the aortic arch. Fusion of the buds occurs a n d the thymus assumes its position and form in the m e d i a s t i n u m . T h y m i c tissue m a y present along the route of descent. 13 This route starts at the paratonsillar fossa along the carotid sheath and continues into the chest. In an autopsy study, Wenglowski showed that in two of ten adults, t h y m i c rests were found in the neck, b u t more significantly thymic rests were identified in the neck in approximately one-third of the children examined. 14
CERVICAL THYMIC CYSTS
These rests can present clinically as aberrant thymus, thymorna or thymic cyst. The exact etiology of the cyst is not clear. In 1938, Speer ~5 postulated five reasons for the development of cervical thymic cysts: (1) they may represent embryonal remnants of branchial clefts, thymic tubules, and thymopharyngeal clefts; (2) they may be caused by sequestration products in the involution of the thymus; (3) there may be neoplastic changes in the lymphoid, cytoreticular, or connective tissue; (4) degeneration of Hassall's corpuscles may result in cyst formation; (5) they may arise from the lymphatic, vasculature or connective tissue that has arrested in the various stages of thymic development, hyperplasia or involution. Currently these cysts are thought to occur either as congenital (by the persistence of the thymopharyngeal tracts) or acquired (the degeneration of Hassall's corpuscles and other components of the thymus). These two concepts explain the histologic findings. 3 Thymic cysts can be unilocular or multilocular. They contain either clear or straw-colored fluid. There have been reports of hemorrhage into the cysts, 16 similar to case 3. The cyst wall can be lined with spindle-shaped, spiral, or columnar cells. Thymic elements are in intimate contact with the cyst wall. Hassall's corpuscles are evident. Giant cell reaction is common. Cholesterol crystals can be demonstrated in either the fluid or cyst wall. Without these distinguishing features, these cysts cannot be differentiated from the branchial cleft cyst. 17 Eighty to ninety percent of these cysts are asymptomatic neck masses. Seven of ten patients presented this way. Approximately 10% of the patients will have complaints of dysphagia, dyspnea, cervical pain, or hoarsenessJ s While literature reports an approximate 3:2 male dominance, our patients show a reverse distribution. The average age of surgery is 8.3 years. The duration of the mass is usually <6 months. In patients with a palpable mass, seven of eight reported it present for <6 weeks. While not always stated in other reports, a URI occurred in seven of the patients with a neck mass. Fluctuation in size as well as rapid enlargement can also occur. This happened in two of three patients while in the hospital. Hyperplasia of the thymus was reported with infections or vaccinations. ~9 The histology of hyperplasia demonstrates increased cellularity of the thymic element, as well as presence of germinal centers consistent with a reaction of an infectious stimulus. The majority of cysts are found in the lower third of the neck, anterior to but extending beneath the sternocleidomastoid muscle. All have been described as mobile. Reports show that 50% of thymic cysts extend
659
into the mediastinum. In our patients, five of ten had this extension. This connection may be a contiguous cyst, duct, solid cord, or remnant of thymic tissue. There has been a 2:1 left to right side predominance with other locations including midline, intratracheal posterior pharynx, and the pyriform sinus. 2~Preoperatively to date, none of the cysts has been diagnosed correctly. 1'18 In one case (patient 8), the correct diagnosis was made by one of the authors. While the exact preoperative diagnosis may be unimportant, the possibility of mediastinal extension should be considered in planning the surgical approach. The appearance of normal and abnormal thymus in a child by CT scan has been well described. 2L22 Ultrasound has also been used to identify mediastinal extensions and neck masses. 23 Again, while the exact diagnosis may be unimportant, knowledge of the extent of the lesion is helpful to the surgeon. We currently recommend the use of ultrasonography as a screen mode followed by CT scan if necessary. Also, documenting the presence of tracheal compression may serve as a guide to early postoperative respiratory problems. Surgery remains the choice of therapy. Complete excision is curative. While there is a recorded 2% recurrence rate in adults, there has been no recurrence in children. In our follow-up period there has been no recurrence. Whether the development of a second cyst can occur in adulthood is unknown. In children, there has not been a report of malignant degeneration, myasthenia gravis, or immunologic deficiencies following removal of a cervical thymic cyst. Possibly this is due to the fact that the thymic cyst contains no active, solid, thymic tissue. Because of this fact, thymic cysts should be completely excised, sparing vital structures. The cysts may adhere to the vagus nerve, carotid artery, jugular vein, phrenic nerve, and recurrent laryngeal nerve. It has been stated that thymic cysts are rarely associated with respiratory compromise. However, two reports documented respiratory problems in the preoperative period in newborns, a'5 In our case, one patient required both preoperative and postoperative respiratory support and two others required airway management in the early postoperative period. Documenting tracheal compression prior to surgery may serve as a guide to determine which patient may develop problems. It is suggested that the tenseness of the cyst and the compression on the young and soft trachea may result in a form of tracheal malacia which resolves over the long-term after treatment. 24"25Again, all patients that demonstrated respiratory problems in the perioperative period had no long-term sequelae. In summary, ten patients underwent excision of a
660
WAGNER ET AL
c e r v i c a l t h y m i c cyst. T h r e e d e v e l o p e d s e v e r e r e s p i r a t o r y p r o b l e m s in t h e p e r i o p e r a t i v e phase. A l l t h r e e h a d d e m o n s t r a t e d t r a c h e a l c o m p r e s s i o n p r i o r to s u r g e r y on i m a g i n g studies. T h y m i c cysts s h o u l d be c o n s i d e r e d in d i a g n o s i n g n e c k m a s s e s in c h i l d r e n , a n d t r e a t e d surgic a l l y as t h e b e n i g n lesions t h a t t h e y are, r e a l i z i n g t h a t p o t e n t i a l r e s p i r a t o r y p r o b l e m s m a y be a p p a r e n t in t h e p e r i o p e r a t i v e period.
REFERENCES 1. Jensen JH, Larsen JL, Asschenfeldt P: Congenital thymic cysts in the neck. Int J Pediatr Otorhinolaryngol 6:95-100, 1983 2. Barat M, Sciubba J J, Abramson AL: Cervical thymic cyst: Case report and review of literature. Laryngoscope 85:89-91, 1985 3. Sanusi ID, Carrington PR, Adams DN: Cervical thymic cyst. Arch Dermatol 118:122-124, 1982 4. Ranier JM, Rowe LD: Progressive neonatal airway obstruction secondary to cervical thymic cyst. Otolaryngol Head Neck Surg 89:723-725, 1981 5. Rosevear WH, Singer MI: Symptomatic cervical thymic cyst in a neonate. Otolaryngol Head Neck Surg 89:738-741, 1981 6. Chiba T, Kisugi T, Igura H, et al: Persistent cervical thymus with a small cyst in a newborn infant. Z Kinderchir 39:265-266, 1984 7. Becker GD, Rudolf R: Cervical thymic cyst. Otolaryngol Head Neck Surg 93:807-809, 1985 8. AI-Shihabr BM, Jackson JMcG: Cervical thymic cyst. J Laryngol Otol 96:181-189, 1982 9. Pollosson A, Piery M: Un car d'epithelioma primitif du thymus. Prov Med Lyons 15:1-4, 1901 I0. Hyde TL, Sellers ED, Owen M: Thymic cyst of the neck. Tex State J Med 39:539-540, 1944
11. Johnsen N J, BrEtlau, P: Cervical thymic cyst. Acta Otolaryngol 82:143-146, 1976 12. Barrick B, O'Kell RT: Thymic cysts and remnant cervical thymus. J Pediatr Surg 4:355-357, 1969 13. Reiner M, Beck RA: Cervical thymic cysts in children. Am J Surg 139:704-707, 1980 14. Wenglowski R: Ueber de Halsfirtern and cysten. Arch Klein Chir 100:789, 1912-1913 15. Speer FD: Thymic cysts. NY Med Coll Fower Hosp Bull 1:142-150, 1938 16. Moskowitz PS, Noon MA, McAlister WH, et al: Thymic cyst hemorrhage: A cause of acute, symptomatic mediastinal widening in children with aplastic anemia. A JR 134:832-836, 1986 17. Hanid TK, Johnson AG, Kay L: Cervical thymic cyst. J Pediatr Surg 10:141-142, 1975 18. Guba AM, Adam AE, Jaques DA, et al: Cervical presentation of thymic cysts. Am J Surg 136:430-436, 1978 19. Tovi F, Mares AJ: The aberrant cervical thymus, embrylogy, pathology and clinical implication. Am J Surg 136:631-637, 1978 20. Mikal S: Cervical thymic cyst, case report and review of the literature. Arch Surg 109:558-562, 1974 21. Salonen OLM, Kivisarri ML, Somer JK: Computed tomography of the thymus of children under 10 years. Pediatr Radiol 14:373-375, 1984 22. St Amour TE, Siegel M J, Glazer HS, et al: CT appearances of the normal and abnormal thymus in childhood. J Comput Assist Tomogr 11:645-650, 1987 23. Claus D, Coppen JP: Sonography of mediastinal masses in infants and children. Ann Radiol 27:150-159, 1984 24. Cooper DK, Chrispin AR, de Leval M, et al: Cryptic mediastinal masses causing airway obstruction. Arch Dis Child 58:306-309, 1983 25. Azizkhan RG, Dudgeon DL, Buck JR, et al: Life-threatening airway obstruction as a complication to the management of mediastinal masses in children. J Pediatr Surg 20:816-822, 1985
rHILE THE ORIGIN of thymic cysts has long
W been recognized, they have been considered uncommon lesions in the diagnosis of pediatric neck masses and (except for diagnosis) have been without clinical importance. Of the 75 cysts reported in patients <20 years of age, all were described as asymptomatic and few associated with respiratory embarrassment. ~s Since 1963 at St. Christopher's Hospital for Children and Arkansas Children's Hospital, ten patients underwent surgery involving removal of cervical thymic cyst. These patients are reviewed with special emphasis on three in whom respiratory problems developed.
Journal of PediatricSurgery, Vol 23, No 7 (July), 1988: pp 657-660
MATERIALS AND METHODS There were ten children ranging in age from newborn to 14 years who underwent subsequent removal of thymic cysts from the neck. Four of these occurred in boys and six occurred in girls. Two underwent neck exploration; one for Grave's disease and the other for hyperparathyroidism, and were found to have an associated thymic cyst with the primary disease. The remaining eight were operated on for a cystic neck mass (Table 1). Seven of eight had 2 URI within 2 weeks prior to presentation. This coincided with the rapid increase in mass size. None had any symptoms of neuromuscular disorders in their medical history. All eight had a mobile cystic mass located anterior to but extending beneath the lower third of the sternocleidomastoid muscle. The size of the mass ranged from 3.0 to 8.5 cm at its largest diameter. None of the patients was noted to have any abnormal hematologic studies prior to surgery. Preperative diagnosis includes cystic hygroma/branchial cleft cyst (five), lymphoma (one), teratoma (one), and thymic cyst (one). Tracheal and/or esophageal compression were demonstrated by either barium swallow, neck films, chest x-rays, computerized axial tomography, or ultrasound in five patients. Of this group, one developed severe respiratory problems requiring preoperative intubation and postoperative airway management. Two others required airway management immediately after surgery. All masses were excised through a cervical incision, with two requiring partial sternotomy for mediastinal extension. All specimens were cystic, containing brownish fluid. Histology showed Hassall's corpuscles, giant cell reaction, and cholesterol crystals diagnostic of thymic cyst. Follow-up on all patients ranged from 4 months until discharge at 4 years. During this period there were no recurrences, no residual complications, and no respiratory sequelae.
CASE REPORTS
Case I A 9-year-old black male was evaluated for a mass on the left side of the neck of 1 week's duration. He had a history of recent URI subsequent to the development of the mass. Upon physical examination, the lesion measured 3 x 5 cm, was mobile, and was located on the lower third of the neck, anterior to but extending below the sternocleidomastoid muscle. Chest x-rays indicated the trachea was compressed and deviated. Upon barium swallow, esophageal compression was seen. The patient underwent excision of the lesion through a cervical approach. The lesion was noted to extend into the
From the University of Arkansas for Medical Sciences and Arkansas Children's Hospital, Little Rock; and St. Christopher's Hospital for Children, Philadelphia. Presented at the 36th Annual Meeting of the Surgical Section of the American Academy of Pediatrics, New Orleans, October 31 to November 2, 1987. Address reprint requests tO Charles IV. Wagner, MD, Arkansas Children's Hospital, 800 Marshall St, Little Rock, A R 722023591. 9 1988 by Grune & Stratton, Inc. 0022-3468/88/2307-0015503.00/0
657
658
WAGNER ET AL Table 1. Patients With a Palpable Cervical Mass
Patient No.
Age (yr)/Sex
Size (cm)/URI History
1
11/F
8/+
2
9/M
3.5/+
PROV DX
Location
Cystic hygroma
R
Teratoma
L
3
12/F
4/§
Lymphoma
L
4 5
7/F 4/F
4/+ 4/+
Branchial cleft cyst Cystic hygroma
R R
6 7 8
3 d/M 5/M 4/F
5/-6/+ 8.5/+
Branchial cleft cyst Branchial cleft cyst Thymic cyst
L L L
Radiologic Studies (trachea compression) Neck films, BA swallow CXR, BA swallow CXR, ultrasound ND CXR, neck films, BA swallow, CT, ultrasound
Neck ND Ultrasound
Recurrence/ Follow-up + +
No/2 yr
+
No~3 yr
+ + +
No/4 yr
+ 33333-
No/3 yr No/1 yr
No/3 yr No/4 mo No/6 mo
Abbreviations: PROV DX, provisional diagnosis; BA, barium; CXR, chest x-ray; ND, not done.
mediastinum and a sternotomy was performed to aid in total resection. Twelve hours postoperatively,he developed severe stridor and respiratory distress. There was no sign of hematoma or external compression, but to relieve the distress, a tracheostomy was performed. The respiratory distress quickly resolved and the child underwent decannulation in 1 month without difficulty.At 3 years follow-up, he showed no recurrence and no respiratory problems.
Case 2 A 4-year-old black female had a 2-week history of an enlarging mass on the right side of the neck and dysphagia. She had a history of previousURI. Upon physical examination the mass was 3 • 4 cm, mobile, and located at the lower third of the neck, anterior to but extending below the sternocleidomastoidmuscle. Tracheal compression was demonstrated on lateral neck films,deviationof the cervical esophagus on barium swallow, and tracheal compression on computerized tomography (CT) scan (Fig 1). During preoperative evaluation, the cyst doubled in size. Excision was accomplished through a cervical approach with a partial sternotomy. In the early postoperative course, she developed stridor and subsequent right upper lobe, and total left lung atelectasis. She underwent laryngoscopy and bronchoscopy,and was noted to have tracheal narrowing. She required intubation for 72 hours and vigorous pulmonary care for 3 weeks in order to resolveher respiratory problem.At 1 year she showed no signs of recurrence or respiratory problems. The followup CT scan showed a normal trachea.
Fig 1. CT scan of lower cervical region shows a right cyst mass compression and deviation of trachea.
Case 3 Upon physical examination, a newborn boy was noted to have a mass in the left cervical region. Forty-eight hours after birth the mass rapidly enlarged. The patient developed respiratory problems and required intubation. He underwent excision of this through a cervical approach. The mass showed signs of hemorrhage into the cyst. Postoperatively he was extubated within 48 hours of surgery. Two years after surgery he had no respiratory problems and no signs of recurrence. DISCUSSION I n 190 l, Pollosson and Piery m a d e the first a t t e m p t at surgical excision of this lesion in a n i n f a n t .9 T h e first successful excision in a child was performed by Hyde et al in 1944.1~ Cases have been sporadic, a n d to date, 75 have occurred in children < 2 0 years. W i t h the addition of these ten cases, over 70% of cervical thymic cysts are in patients < 2 0 years of age. Johnsen and Br~tlau ll have suggested that the prevalence in childhood m a y be due to the fact that the t h y m u s undergoes its greatest development in the p r e p u b e r t y period. Barrick a n d O'Kel112 state further that the thymus reaches its greatest relative size from age 2 to 4, with its greatest absolute size at puberty. W i t h regard to embryology, the t h y m u s originates from the third branchial pouch bilaterally in the 6th week of development. D u r i n g weeks 7 a n d 8, the t h y m u s elongates and descends to the level of the aortic arch. Fusion of the buds occurs a n d the thymus assumes its position and form in the m e d i a s t i n u m . T h y m i c tissue m a y present along the route of descent. 13 This route starts at the paratonsillar fossa along the carotid sheath and continues into the chest. In an autopsy study, Wenglowski showed that in two of ten adults, t h y m i c rests were found in the neck, b u t more significantly thymic rests were identified in the neck in approximately one-third of the children examined. 14
CERVICAL THYMIC CYSTS
These rests can present clinically as aberrant thymus, thymorna or thymic cyst. The exact etiology of the cyst is not clear. In 1938, Speer ~5 postulated five reasons for the development of cervical thymic cysts: (1) they may represent embryonal remnants of branchial clefts, thymic tubules, and thymopharyngeal clefts; (2) they may be caused by sequestration products in the involution of the thymus; (3) there may be neoplastic changes in the lymphoid, cytoreticular, or connective tissue; (4) degeneration of Hassall's corpuscles may result in cyst formation; (5) they may arise from the lymphatic, vasculature or connective tissue that has arrested in the various stages of thymic development, hyperplasia or involution. Currently these cysts are thought to occur either as congenital (by the persistence of the thymopharyngeal tracts) or acquired (the degeneration of Hassall's corpuscles and other components of the thymus). These two concepts explain the histologic findings. 3 Thymic cysts can be unilocular or multilocular. They contain either clear or straw-colored fluid. There have been reports of hemorrhage into the cysts, 16 similar to case 3. The cyst wall can be lined with spindle-shaped, spiral, or columnar cells. Thymic elements are in intimate contact with the cyst wall. Hassall's corpuscles are evident. Giant cell reaction is common. Cholesterol crystals can be demonstrated in either the fluid or cyst wall. Without these distinguishing features, these cysts cannot be differentiated from the branchial cleft cyst. 17 Eighty to ninety percent of these cysts are asymptomatic neck masses. Seven of ten patients presented this way. Approximately 10% of the patients will have complaints of dysphagia, dyspnea, cervical pain, or hoarsenessJ s While literature reports an approximate 3:2 male dominance, our patients show a reverse distribution. The average age of surgery is 8.3 years. The duration of the mass is usually <6 months. In patients with a palpable mass, seven of eight reported it present for <6 weeks. While not always stated in other reports, a URI occurred in seven of the patients with a neck mass. Fluctuation in size as well as rapid enlargement can also occur. This happened in two of three patients while in the hospital. Hyperplasia of the thymus was reported with infections or vaccinations. ~9 The histology of hyperplasia demonstrates increased cellularity of the thymic element, as well as presence of germinal centers consistent with a reaction of an infectious stimulus. The majority of cysts are found in the lower third of the neck, anterior to but extending beneath the sternocleidomastoid muscle. All have been described as mobile. Reports show that 50% of thymic cysts extend
659
into the mediastinum. In our patients, five of ten had this extension. This connection may be a contiguous cyst, duct, solid cord, or remnant of thymic tissue. There has been a 2:1 left to right side predominance with other locations including midline, intratracheal posterior pharynx, and the pyriform sinus. 2~Preoperatively to date, none of the cysts has been diagnosed correctly. 1'18 In one case (patient 8), the correct diagnosis was made by one of the authors. While the exact preoperative diagnosis may be unimportant, the possibility of mediastinal extension should be considered in planning the surgical approach. The appearance of normal and abnormal thymus in a child by CT scan has been well described. 2L22 Ultrasound has also been used to identify mediastinal extensions and neck masses. 23 Again, while the exact diagnosis may be unimportant, knowledge of the extent of the lesion is helpful to the surgeon. We currently recommend the use of ultrasonography as a screen mode followed by CT scan if necessary. Also, documenting the presence of tracheal compression may serve as a guide to early postoperative respiratory problems. Surgery remains the choice of therapy. Complete excision is curative. While there is a recorded 2% recurrence rate in adults, there has been no recurrence in children. In our follow-up period there has been no recurrence. Whether the development of a second cyst can occur in adulthood is unknown. In children, there has not been a report of malignant degeneration, myasthenia gravis, or immunologic deficiencies following removal of a cervical thymic cyst. Possibly this is due to the fact that the thymic cyst contains no active, solid, thymic tissue. Because of this fact, thymic cysts should be completely excised, sparing vital structures. The cysts may adhere to the vagus nerve, carotid artery, jugular vein, phrenic nerve, and recurrent laryngeal nerve. It has been stated that thymic cysts are rarely associated with respiratory compromise. However, two reports documented respiratory problems in the preoperative period in newborns, a'5 In our case, one patient required both preoperative and postoperative respiratory support and two others required airway management in the early postoperative period. Documenting tracheal compression prior to surgery may serve as a guide to determine which patient may develop problems. It is suggested that the tenseness of the cyst and the compression on the young and soft trachea may result in a form of tracheal malacia which resolves over the long-term after treatment. 24"25Again, all patients that demonstrated respiratory problems in the perioperative period had no long-term sequelae. In summary, ten patients underwent excision of a
660
WAGNER ET AL
c e r v i c a l t h y m i c cyst. T h r e e d e v e l o p e d s e v e r e r e s p i r a t o r y p r o b l e m s in t h e p e r i o p e r a t i v e phase. A l l t h r e e h a d d e m o n s t r a t e d t r a c h e a l c o m p r e s s i o n p r i o r to s u r g e r y on i m a g i n g studies. T h y m i c cysts s h o u l d be c o n s i d e r e d in d i a g n o s i n g n e c k m a s s e s in c h i l d r e n , a n d t r e a t e d surgic a l l y as t h e b e n i g n lesions t h a t t h e y are, r e a l i z i n g t h a t p o t e n t i a l r e s p i r a t o r y p r o b l e m s m a y be a p p a r e n t in t h e p e r i o p e r a t i v e period.
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