Pediatric and Developmental Pathology 17, 400-405, 2014 DOI: 10.2350/14-04-1459-CR.1 © 2014 Society fo r Pediatric Pathology
Benign Triton Tumor: Multidisciplinary Approach to Diagnosis and Treatment Raj T hakrar , 1 C aroline
D. R obson , 2 Sara O. V argas, 3 John G. M
eara , 4
R eza Rahbar , 5
and
Edw ard R. Sm it h 1* d e p a rtm e n t d e p a rtm e n t d e p a rtm e n t d e p a rtm e n t d e p a rtm e n t
of of of of of
Received March
Neurosurgery, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA Radiology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA Pathology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA Plastic Surgery, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA Otolaryngology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA 7,
2014; accepted July 14, 2014; published online July 14, 2014.
ABSTRACT
Benign Triton tumor (neuromuscular choristoma) is a rare mass that most commonly occurs as a multinodular expansion of tissue in or around large nerves. Intracranial occurrence is uncommon. We report on a 4-year-old girl presenting with a right-sided facial mass and trismus. Imaging revealed a large, complex mass extending from the ventral aspect of the pons, along the trigeminal nerve, through the foramen ovale, and into the right infratem poral fossa. The lesion was partially enhancing, invaded adjacent infratemporal musculature, was associated with marked overgrowth of the right coronoid process, and induced bony erosion of the middle cranial fossa. After needle biopsy, a multidisciplinary team, including plastic surgery, otolaryngology, and neurosurgery, performed a combined, multistep, single-day surgical approach for resection. Unique to this case was the resection of the coronoid process, a modified middle fossa intradural and extradural approach, coupled with a transfacial infratem poral approach. Microscopically, the resected tissue showed skeletal muscle, fibrous tissue, and nerve in a disorganized arrangement characteristic of a benign Triton tumor. We present this case to illustrate diagnostic clues and pitfalls in the preoperative evaluation of a benign Triton tumor. We also highlight the pathologist’s role as a partner in a multidisciplinary approach to diagnosis and treatment of this rare pediatric mass, potentially the largest Triton tumor in the head reported to date. Key words: benign Triton tumor, brain tumor, multidis
ciplinary, neuromuscular choristoma, rhabdomyoma, skull base
*Corresponding author, e-mail: [email protected]
Benign Triton tumors (also referred to as neuromuscular hamartomas or neuromuscular choristomas) are rare masses that typically present in infancy or childhood, classically, around large peripheral nerve trunks, such as the sciatic nerve or brachial plexus. Histologically, they are characterized by a conglomeration of differentiated skeletal muscle, nerve fibers, and dense fibrous bands [1], The distinction between benign Triton tumor and rhabdomyoma is in many ways semantic, and the term nerve rhabdomyoma is another synonym [2], In the English literature, to our knowledge, 13 cases of benign Triton tumor have been reported to occur in the head and neck region [3-14] and only 4 involved both the infratemporal and intracranial fossae [5]. We report on a benign Triton tumor in a 4-year-old girl, which was striking for its large size and intracranial involvement. In addition to illustrating a rare presentation, we highlight the custom, multidisciplinary approach required to address the unique challenges for successful resection. CASE REPORT Patient presentation
A 4-year-old girl was referred to our institution for the evaluation and treatment of a right-sided facial mass and progressive jaw stiffness. Difficulty opening and closing her mouth had been appreciated for as long as 2 years and had worsened during the 3 months before presentation. She was otherwise healthy and had no personal or family history of tumor, trauma, or major medical illnesses. She was evaluated by plastic surgery, otolaryngology, and neurosurgery, with associated imaging review by neuroradiology. Physical exam revealed fullness in the zygomatic and masseteric regions. The patient could only open her mouth 1.5 cm, limited by mechanical constraints, not by pain. Tongue mobility was normal, the posterior pharynx was clear, palate elevation was symmetric, and her neck exam revealed no lymphadenopathy. Her neurologic
exam was notable for slightly decreased facial sensation on the right side in the V2 and V3 distributions. Radiographic studies included magnetic resonance imaging (MRI) and computerized tomography (CT). The MRI revealed distortion of the upper pons associated with a lobulated tumor involving the right trigeminal nerve and small, cystic foci alongside the right side of the pons and the Meckel cave (Fig. 1A). The otherwise predominantly homogeneous and solid tumor measured approximately 3.6 cm anteroposterior by 4.5 cm craniocaudal by 3.5 cm transverse and extended from the ventral aspect of the pons into the Meckel cave and the cavernous sinus, before descending into the masticator space, where it blended with all of the muscles of mastication. The intracranial component of the tumor appeared markedly hypointense, and some of the signal was isointense, with the diffusely enlarged right muscles of mastication on T2-weighted images and minimally higher signal intensity than the contralateral muscles of mastication (Fig. 1A, B). There was diffuse enhancement of the right muscles of mastication and the tumor, so it was not possible to distinguish between tumoral involvement of muscle and reactive changes within the muscle (Fig. 1C). Despite the chronicity of symptoms, no denervation atrophy of muscle was observed. The CT showed sharply marginated erosion of the foramen ovale and the anterior inferior aspect of the right middle cranial fossa (Fig. 2). A diagnosis of benign Triton tumor was proposed by a radiologist who had previously coauthored a case report on Triton tumor [4], A CT-guided needle biopsy showed histologically benign skeletal muscle cells displaying marked variation in fiber size, set in a fibrous stroma (Fig. 3A). Occasional skeletal muscle nuclei were positive for myogenin. Based on this small biopsy sample, the differential diagnosis included a rhabdomyoma (or benign Triton tumor), a benign fibrous lesion, reachve/regenerative muscle adja cent to an unsampled lesion, or a rhabdomyosarcoma with an unsampled histologically malignant component in addition to markedly well-differentiated areas resembling rhabdomyoma. A previous needle biopsy at an outside institution was reportedly nondiagnostic, but this material was not reviewed at our institution. Findings were reviewed at an interdisciplinary conference, and the decision was made to proceed to operative resection.
Figure 1. A. Axial, fat-suppressed, T 2 -w e ig h te d m agnetic resonance im a g in g (MRI) shows th e lo b u la te d , hypointense tu m o r (short arrow s) arising fro m th e rig h t trig e m in a l nerve. Note th e d is to rtio n o f th e v e n tro la te ra l pons (long arrow ) and adjacent cystic change (arrow heads). The tu m o r
extends in to th e Meckel cave and in to th e cavernous sinus and a n te rio rly th ro u g h a d efe ct in th e skull to blend w ith th e rig h t te m p o ra lis muscle. B. A xial, fat-suppressed, g a d o liniu m -en ha n ced , T 1-w eig hte d MRI a t th e same level shows th e enhancing tu m o r alongside th e rig h t in te rn a l ca ro tid artery. C. Axial, fat-suppressed, g a d o lin iu m -e n hanced, T 1-w eig hte d MRI shows d iffu se e nhancem ent o f th e rig h t muscles o f m astication, especially th e p te ryg o id muscles (arrow ).
B enign T riton T umor
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Figure 2. Axial computed tomography image bone window shows sharply marginated erosion o f the anterior inferior middle cranial fossa (arrows).
Operative treatment A multidisciplinary team, including plastic surgery, otolaryngology, and neurosurgery, performed a coordinat ed, single-day surgical approach for resection. Objectives of surgery included obtaining definitive diagnostic tissue, treating the mechanical difficulties with jaw movement, and tumor debulking. Unique challenges presented by the case included the complex anatomy, from the extracranial tumor in the infratemporal fossa to the intracranial tumor and cystic component in the middle and posterior fossae. Additional complexities included the overgrowth of the coronoid process contributing to the patient’s trismus and the poorly defined nature of the extracranial tumor, which blended with the muscles of mastication, making margins difficult to identify, especially extracranially. Central to the success of the case was coordinated, preoperative planning, outlining the strategy for the approach and delineating specific objectives for each of the surgical teams. Initially, a right frontotemporal craniotomy was per formed. Tumor was found to extend from the middle fossa intradurally, through the defect in the foramen ovale, and then continued extradurally into the infratemporal fossa. The bridge of the tumor through the bony defect was amputated. Radiofrequency ablation was employed to debulk the mass in the infratemporal fossa. A coronoidectomy was performed to remove the markedly hypertrophied coronoid process. These efforts were critical to alleviating the limitation in jaw movement. The case concluded with an intradural resection of the tumor from the dural defect to the posterior fossa.
Pathologic findings Grossly, the resected specimen consisted of numerous fragments of tan-pink to tan-white tissue. Microscopically,
402
R. T h a k r a r
et a l .
all samples showed collections of benign skeletal muscle, fibrous tissue, and nerve (Fig. 3B). The muscle was the most abundant component. It showed variation in fiber size, resembling that seen in degenerative/regenerative change, and was often enveloped by fibrous tissue and focally intermixed with nerve. The fibrous tissue was histologically bland; it enwrapped skeletal muscle bundles and, occasionally, individual fibers. The nerve in most places had the organized appearance of underlying nerve native to the region. However, it was occasionally seen intermixed with muscle and fibrous tissue in a disorganized fashion. These findings con firmed the diagnosis of benign Triton tumor (neuromus cular hamartoma or rhabdomyoma). Cytogenetic analysis of both the needle biopsy and the resection specimen showed a normal female karyotype (46,XX) in both cases. In both the needle biopsy and the frozen section, the fibrous tissue constituted a substantial component of the tissue, and the differential diagnosis of a primarily fibroproliferative lesion could not be excluded; however, a negative [I-catenin immunostain in the biopsy sample helped to rule out desmoid fibromatosis.
Follow-up The patient had an uneventful postoperative course, with the lumbar drain removed on postoperative day 4 and discharge to home on postoperative day 5. Follow-up MRI revealed a small amount of residual tumor alongside the right internal carotid artery, with residual enlargement and enhancement of the muscles of mastication. At last follow-up, 1 year after the operation, the patient was well, except for residual limits in opening of the mouth (10 mm), despite injected botulinum toxin and stretching exercises. Her follow-up plan included serial imaging and continued physical therapy.
DISCUSSION Benign Triton tumors often develop around peripheral nerve trunks [10] but are rarely reported as intracranial lesions. The tumor reported herein represented an unusually large, intracranial, benign Triton tumor of the trigeminal nerve that extended into the masticator space in a young child [5]. The preoperative diagnosis in this case required clinical and pathologic correlation. The bony remodeling and mandibular deformity as well as the smoothly marginated bony erosion indicated a long-standing, benign process. The mild deformity of the pons and apparent origin of the tumor from the trigeminal nerve indicated a neurogenic origin mass. These findings, together with the diffuse involvement of the muscles of mastication, are features that led to the suggestion of benign Triton tumor. Determination of the benign neurogenic nature of the tumor was helpful with both operative planning and pathologic interpretation. It was, however, difficult to determine how much of the signal
Figure 3. A. The needle biopsy showed skeletal muscle with marked variation in fiber size (left panel) and a component of densely collagenized fibrous tissue (right panel), hematoxylin and eosin stain, X200. B. The excisional biopsy showed the more clearly diagnostic hamartomatous disorganization characteristic of benign Triton tumor, w ith intermingling of skeletal muscle, fibrous tissue, and nerve (left panel, hematoxylin and eosin stain, X200). The disorganized nerve component is highlighted by an immunohistochemical stain for S100 protein (right panel, x200). B enign T riton T um or
403
abnormality within the muscles of mastication was attributable to involvement by tumor as opposed to denervation change, although radiographically evident atrophy of the muscle, as might be expected with longstanding denervation, was not seen. The mandible deformity and the involvement of the muscles of mastication presumably both had a role in the long standing mechanical difficulties with jaw movement. The location of the tumor—deep within the mastica tor space—contributed to the relatively late clinical presentation. The patient presented herein illustrates the difficulty that can be encountered interpreting small, needle biopsy samples of benign Triton tumor. In this case, the biopsy specimen lacked a neural component, showing benign skeletal muscle with changes that raised a differential diagnosis of rhabdomyoma (including an incompletely sampled benign Triton tumor), reactive changes adjacent to an unsampled lesion, or, possibly, muscle involvement by a reactive or neoplastic fibroproliferative process. Some authors have indeed interpreted fibrous tissue accompanying a benign Triton tumor to represent a secondary or concurrent “ desmoid tumor” [15], whereas we speculate about the relationship between a benign Triton tumor and a sternocleidomastoid tumor of infancy and other benign head and neck fibromatoses of infancy and early childhood. Because benign Triton tumors can resemble normal skeletal muscle and nerve elements and, in fact, may be best conceived of as hamartomas, difficulty ascertaining whether lesional tissue has been procured is expected to be a common problem in evaluating limited biopsy samples. As a caveat, in rare cases, the elements of a benign Triton tumor may be juxtaposed with histologically malignant elements, such as rhabdomyosarcoma [16]. In this case, the radiographic findings favored benign Triton tumor; combined with the pathology findings, that led us to a decision to proceed with a marginal/subtotal resection, a surgical plan that was reinforced in this case by the intraoperative frozensection analysis. Although our institution has no formal requirement mandating review of outside pathology material before surgery is undertaken, that procedure is highly recom mended. In retrospect, review of the previous needle biopsy material may have been helpful in expediting the workup of this patient. A major lesson from this patient was that a “ nondiagnostic” biopsy may be a clue in the diagnosis of a benign Triton tumor because the abnormal skeletal muscle and fibrous tissue may mimic perturbed tissue adjacent to an unsampled lesion. Given the anatomic complexity of this tumor, the patient was treated by an interdisciplinary team. The particular surgical challenges posed by this case were its intracranial component, which required resection by a neurosurgeon; a large extracranial component, requiring a joint effort by a plastic surgeon and an otolaryngologist; the unusual bony anatomy of the skull base and jaw; and 404
R.
T hakraretal.
the lack of absolute diagnostic certainty in the histologic evaluation of the core needle biopsy and frozen-section material. This patient’s successful recovery was facilitat ed by the detailed preoperative planning and the coordinated, strategic intraoperative execution by the multidisciplinary team. Lastly, we report this case to increase awareness among physicians of all disciplines. Benign Triton tumors should be considered in the differential diagnosis of head and neck tumors affecting infants and children. Aware ness of the diagnosis is helpful for prognostic and therapeutic planning, as demonstrated in this case. CONCLUSION
Benign Triton tumors are exceedingly rare in children. This case highlights the importance of a coordinated, multidisciplinary surgical approach and illustrates the challenges unique to this tumor type, given its large size and intracranial involvement. Preoperative diagnosis can be challenging, and results from a small biopsy sample must be informed by multidisciplinary clinicoradiographic correlation. Preoperative planning is critical to success, with articulation of surgical goals and clear steps outlined for the approach. Good radiographic and clinical outcomes can be achieved surgically, particularly with awareness of the strategy of potentially leaving some small residual tumor at the margins to preserve nerve and muscular function. REFERENCES 1. Weiss SW, Goldblum JR. Enzinger and Weiss’ Soft Tissue Tumors, 5th ed. Philadelphia: Mosby Elsevier, 2008;917-919. 2. Perry A. Benign Triton tumour. In: Fletcher CDM, Bridge JA, Hogendoom PCW, Mertens F, eds. Pathology and Genetics of Tumours of Soft Tissue and Bone, 4th ed. Lyon, France: IARC Press, 2013; 185. World Health Organization Classification of Tumors, vol 5. 3. Amita K, Shankar SV, Nischal KC, Basavaraj HB. Benign triton tumor: a rare entity in head and neck region. Korean J Pathol 2013; 47:74-76. 4. Castro DE, Raghuram K, Phillips CD. Benign triton tumor of the trigeminal nerve. AJNR Am J Neuroradiol 2005;26:967-969. 5. Daley TD, Darling MR, Wehrli B. Benign Triton tumor of the tongue. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008; 105:763-766. 6. Demir Y, Uluoglu O, Ozmen S, Boyacioglu ZM, Atabay K. Neuromuscular hamartoma in the mental region. J Oral Maxillofac Surg 2003;61:397^100. 7. Lena G, Dufour T, Gambarelli D, Chabrol B, Mancini J. Choristoma of the intracranial maxillary nerve in a child. Case report. J Neurosurg 1994;81:788-791. 8. O’Connell JX, Rosenberg AE. Multiple cutaneous neuromuscular choristomas: report of a case and a review of the literature. Am J Surg Pathol 1990;14:93-96. 9. Oeppen RS, Harden SP, Argent JD. Neuromuscular hamartoma: imaging features of a rare paediatric craniofacial tumour. Pediatr Radiol 2003;33:50-52. 10. Tiffee JC, Barnes EL. Neuromuscular hamartomas of the head and neck. Arch Otolaryngol Head Neck Surg 1998;124:212-216. 11. Tobias S, Kim CH, Sade B, Staugaitis SM, Lee JH. Neuromuscular hamartoma of the trigeminal nerve in an adult. Acta Neurochir (Wien) 2006;148:83-87.
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Benign Triton Tumor: Multidisciplinary Approach to Diagnosis and Treatment Raj T hakrar , 1 C aroline
D. R obson , 2 Sara O. V argas, 3 John G. M
eara , 4
R eza Rahbar , 5
and
Edw ard R. Sm it h 1* d e p a rtm e n t d e p a rtm e n t d e p a rtm e n t d e p a rtm e n t d e p a rtm e n t
of of of of of
Received March
Neurosurgery, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA Radiology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA Pathology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA Plastic Surgery, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA Otolaryngology, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA 7,
2014; accepted July 14, 2014; published online July 14, 2014.
ABSTRACT
Benign Triton tumor (neuromuscular choristoma) is a rare mass that most commonly occurs as a multinodular expansion of tissue in or around large nerves. Intracranial occurrence is uncommon. We report on a 4-year-old girl presenting with a right-sided facial mass and trismus. Imaging revealed a large, complex mass extending from the ventral aspect of the pons, along the trigeminal nerve, through the foramen ovale, and into the right infratem poral fossa. The lesion was partially enhancing, invaded adjacent infratemporal musculature, was associated with marked overgrowth of the right coronoid process, and induced bony erosion of the middle cranial fossa. After needle biopsy, a multidisciplinary team, including plastic surgery, otolaryngology, and neurosurgery, performed a combined, multistep, single-day surgical approach for resection. Unique to this case was the resection of the coronoid process, a modified middle fossa intradural and extradural approach, coupled with a transfacial infratem poral approach. Microscopically, the resected tissue showed skeletal muscle, fibrous tissue, and nerve in a disorganized arrangement characteristic of a benign Triton tumor. We present this case to illustrate diagnostic clues and pitfalls in the preoperative evaluation of a benign Triton tumor. We also highlight the pathologist’s role as a partner in a multidisciplinary approach to diagnosis and treatment of this rare pediatric mass, potentially the largest Triton tumor in the head reported to date. Key words: benign Triton tumor, brain tumor, multidis
ciplinary, neuromuscular choristoma, rhabdomyoma, skull base
*Corresponding author, e-mail: [email protected]
Benign Triton tumors (also referred to as neuromuscular hamartomas or neuromuscular choristomas) are rare masses that typically present in infancy or childhood, classically, around large peripheral nerve trunks, such as the sciatic nerve or brachial plexus. Histologically, they are characterized by a conglomeration of differentiated skeletal muscle, nerve fibers, and dense fibrous bands [1], The distinction between benign Triton tumor and rhabdomyoma is in many ways semantic, and the term nerve rhabdomyoma is another synonym [2], In the English literature, to our knowledge, 13 cases of benign Triton tumor have been reported to occur in the head and neck region [3-14] and only 4 involved both the infratemporal and intracranial fossae [5]. We report on a benign Triton tumor in a 4-year-old girl, which was striking for its large size and intracranial involvement. In addition to illustrating a rare presentation, we highlight the custom, multidisciplinary approach required to address the unique challenges for successful resection. CASE REPORT Patient presentation
A 4-year-old girl was referred to our institution for the evaluation and treatment of a right-sided facial mass and progressive jaw stiffness. Difficulty opening and closing her mouth had been appreciated for as long as 2 years and had worsened during the 3 months before presentation. She was otherwise healthy and had no personal or family history of tumor, trauma, or major medical illnesses. She was evaluated by plastic surgery, otolaryngology, and neurosurgery, with associated imaging review by neuroradiology. Physical exam revealed fullness in the zygomatic and masseteric regions. The patient could only open her mouth 1.5 cm, limited by mechanical constraints, not by pain. Tongue mobility was normal, the posterior pharynx was clear, palate elevation was symmetric, and her neck exam revealed no lymphadenopathy. Her neurologic
exam was notable for slightly decreased facial sensation on the right side in the V2 and V3 distributions. Radiographic studies included magnetic resonance imaging (MRI) and computerized tomography (CT). The MRI revealed distortion of the upper pons associated with a lobulated tumor involving the right trigeminal nerve and small, cystic foci alongside the right side of the pons and the Meckel cave (Fig. 1A). The otherwise predominantly homogeneous and solid tumor measured approximately 3.6 cm anteroposterior by 4.5 cm craniocaudal by 3.5 cm transverse and extended from the ventral aspect of the pons into the Meckel cave and the cavernous sinus, before descending into the masticator space, where it blended with all of the muscles of mastication. The intracranial component of the tumor appeared markedly hypointense, and some of the signal was isointense, with the diffusely enlarged right muscles of mastication on T2-weighted images and minimally higher signal intensity than the contralateral muscles of mastication (Fig. 1A, B). There was diffuse enhancement of the right muscles of mastication and the tumor, so it was not possible to distinguish between tumoral involvement of muscle and reactive changes within the muscle (Fig. 1C). Despite the chronicity of symptoms, no denervation atrophy of muscle was observed. The CT showed sharply marginated erosion of the foramen ovale and the anterior inferior aspect of the right middle cranial fossa (Fig. 2). A diagnosis of benign Triton tumor was proposed by a radiologist who had previously coauthored a case report on Triton tumor [4], A CT-guided needle biopsy showed histologically benign skeletal muscle cells displaying marked variation in fiber size, set in a fibrous stroma (Fig. 3A). Occasional skeletal muscle nuclei were positive for myogenin. Based on this small biopsy sample, the differential diagnosis included a rhabdomyoma (or benign Triton tumor), a benign fibrous lesion, reachve/regenerative muscle adja cent to an unsampled lesion, or a rhabdomyosarcoma with an unsampled histologically malignant component in addition to markedly well-differentiated areas resembling rhabdomyoma. A previous needle biopsy at an outside institution was reportedly nondiagnostic, but this material was not reviewed at our institution. Findings were reviewed at an interdisciplinary conference, and the decision was made to proceed to operative resection.
Figure 1. A. Axial, fat-suppressed, T 2 -w e ig h te d m agnetic resonance im a g in g (MRI) shows th e lo b u la te d , hypointense tu m o r (short arrow s) arising fro m th e rig h t trig e m in a l nerve. Note th e d is to rtio n o f th e v e n tro la te ra l pons (long arrow ) and adjacent cystic change (arrow heads). The tu m o r
extends in to th e Meckel cave and in to th e cavernous sinus and a n te rio rly th ro u g h a d efe ct in th e skull to blend w ith th e rig h t te m p o ra lis muscle. B. A xial, fat-suppressed, g a d o liniu m -en ha n ced , T 1-w eig hte d MRI a t th e same level shows th e enhancing tu m o r alongside th e rig h t in te rn a l ca ro tid artery. C. Axial, fat-suppressed, g a d o lin iu m -e n hanced, T 1-w eig hte d MRI shows d iffu se e nhancem ent o f th e rig h t muscles o f m astication, especially th e p te ryg o id muscles (arrow ).
B enign T riton T umor
401
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Figure 2. Axial computed tomography image bone window shows sharply marginated erosion o f the anterior inferior middle cranial fossa (arrows).
Operative treatment A multidisciplinary team, including plastic surgery, otolaryngology, and neurosurgery, performed a coordinat ed, single-day surgical approach for resection. Objectives of surgery included obtaining definitive diagnostic tissue, treating the mechanical difficulties with jaw movement, and tumor debulking. Unique challenges presented by the case included the complex anatomy, from the extracranial tumor in the infratemporal fossa to the intracranial tumor and cystic component in the middle and posterior fossae. Additional complexities included the overgrowth of the coronoid process contributing to the patient’s trismus and the poorly defined nature of the extracranial tumor, which blended with the muscles of mastication, making margins difficult to identify, especially extracranially. Central to the success of the case was coordinated, preoperative planning, outlining the strategy for the approach and delineating specific objectives for each of the surgical teams. Initially, a right frontotemporal craniotomy was per formed. Tumor was found to extend from the middle fossa intradurally, through the defect in the foramen ovale, and then continued extradurally into the infratemporal fossa. The bridge of the tumor through the bony defect was amputated. Radiofrequency ablation was employed to debulk the mass in the infratemporal fossa. A coronoidectomy was performed to remove the markedly hypertrophied coronoid process. These efforts were critical to alleviating the limitation in jaw movement. The case concluded with an intradural resection of the tumor from the dural defect to the posterior fossa.
Pathologic findings Grossly, the resected specimen consisted of numerous fragments of tan-pink to tan-white tissue. Microscopically,
402
R. T h a k r a r
et a l .
all samples showed collections of benign skeletal muscle, fibrous tissue, and nerve (Fig. 3B). The muscle was the most abundant component. It showed variation in fiber size, resembling that seen in degenerative/regenerative change, and was often enveloped by fibrous tissue and focally intermixed with nerve. The fibrous tissue was histologically bland; it enwrapped skeletal muscle bundles and, occasionally, individual fibers. The nerve in most places had the organized appearance of underlying nerve native to the region. However, it was occasionally seen intermixed with muscle and fibrous tissue in a disorganized fashion. These findings con firmed the diagnosis of benign Triton tumor (neuromus cular hamartoma or rhabdomyoma). Cytogenetic analysis of both the needle biopsy and the resection specimen showed a normal female karyotype (46,XX) in both cases. In both the needle biopsy and the frozen section, the fibrous tissue constituted a substantial component of the tissue, and the differential diagnosis of a primarily fibroproliferative lesion could not be excluded; however, a negative [I-catenin immunostain in the biopsy sample helped to rule out desmoid fibromatosis.
Follow-up The patient had an uneventful postoperative course, with the lumbar drain removed on postoperative day 4 and discharge to home on postoperative day 5. Follow-up MRI revealed a small amount of residual tumor alongside the right internal carotid artery, with residual enlargement and enhancement of the muscles of mastication. At last follow-up, 1 year after the operation, the patient was well, except for residual limits in opening of the mouth (10 mm), despite injected botulinum toxin and stretching exercises. Her follow-up plan included serial imaging and continued physical therapy.
DISCUSSION Benign Triton tumors often develop around peripheral nerve trunks [10] but are rarely reported as intracranial lesions. The tumor reported herein represented an unusually large, intracranial, benign Triton tumor of the trigeminal nerve that extended into the masticator space in a young child [5]. The preoperative diagnosis in this case required clinical and pathologic correlation. The bony remodeling and mandibular deformity as well as the smoothly marginated bony erosion indicated a long-standing, benign process. The mild deformity of the pons and apparent origin of the tumor from the trigeminal nerve indicated a neurogenic origin mass. These findings, together with the diffuse involvement of the muscles of mastication, are features that led to the suggestion of benign Triton tumor. Determination of the benign neurogenic nature of the tumor was helpful with both operative planning and pathologic interpretation. It was, however, difficult to determine how much of the signal
Figure 3. A. The needle biopsy showed skeletal muscle with marked variation in fiber size (left panel) and a component of densely collagenized fibrous tissue (right panel), hematoxylin and eosin stain, X200. B. The excisional biopsy showed the more clearly diagnostic hamartomatous disorganization characteristic of benign Triton tumor, w ith intermingling of skeletal muscle, fibrous tissue, and nerve (left panel, hematoxylin and eosin stain, X200). The disorganized nerve component is highlighted by an immunohistochemical stain for S100 protein (right panel, x200). B enign T riton T um or
403
abnormality within the muscles of mastication was attributable to involvement by tumor as opposed to denervation change, although radiographically evident atrophy of the muscle, as might be expected with longstanding denervation, was not seen. The mandible deformity and the involvement of the muscles of mastication presumably both had a role in the long standing mechanical difficulties with jaw movement. The location of the tumor—deep within the mastica tor space—contributed to the relatively late clinical presentation. The patient presented herein illustrates the difficulty that can be encountered interpreting small, needle biopsy samples of benign Triton tumor. In this case, the biopsy specimen lacked a neural component, showing benign skeletal muscle with changes that raised a differential diagnosis of rhabdomyoma (including an incompletely sampled benign Triton tumor), reactive changes adjacent to an unsampled lesion, or, possibly, muscle involvement by a reactive or neoplastic fibroproliferative process. Some authors have indeed interpreted fibrous tissue accompanying a benign Triton tumor to represent a secondary or concurrent “ desmoid tumor” [15], whereas we speculate about the relationship between a benign Triton tumor and a sternocleidomastoid tumor of infancy and other benign head and neck fibromatoses of infancy and early childhood. Because benign Triton tumors can resemble normal skeletal muscle and nerve elements and, in fact, may be best conceived of as hamartomas, difficulty ascertaining whether lesional tissue has been procured is expected to be a common problem in evaluating limited biopsy samples. As a caveat, in rare cases, the elements of a benign Triton tumor may be juxtaposed with histologically malignant elements, such as rhabdomyosarcoma [16]. In this case, the radiographic findings favored benign Triton tumor; combined with the pathology findings, that led us to a decision to proceed with a marginal/subtotal resection, a surgical plan that was reinforced in this case by the intraoperative frozensection analysis. Although our institution has no formal requirement mandating review of outside pathology material before surgery is undertaken, that procedure is highly recom mended. In retrospect, review of the previous needle biopsy material may have been helpful in expediting the workup of this patient. A major lesson from this patient was that a “ nondiagnostic” biopsy may be a clue in the diagnosis of a benign Triton tumor because the abnormal skeletal muscle and fibrous tissue may mimic perturbed tissue adjacent to an unsampled lesion. Given the anatomic complexity of this tumor, the patient was treated by an interdisciplinary team. The particular surgical challenges posed by this case were its intracranial component, which required resection by a neurosurgeon; a large extracranial component, requiring a joint effort by a plastic surgeon and an otolaryngologist; the unusual bony anatomy of the skull base and jaw; and 404
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the lack of absolute diagnostic certainty in the histologic evaluation of the core needle biopsy and frozen-section material. This patient’s successful recovery was facilitat ed by the detailed preoperative planning and the coordinated, strategic intraoperative execution by the multidisciplinary team. Lastly, we report this case to increase awareness among physicians of all disciplines. Benign Triton tumors should be considered in the differential diagnosis of head and neck tumors affecting infants and children. Aware ness of the diagnosis is helpful for prognostic and therapeutic planning, as demonstrated in this case. CONCLUSION
Benign Triton tumors are exceedingly rare in children. This case highlights the importance of a coordinated, multidisciplinary surgical approach and illustrates the challenges unique to this tumor type, given its large size and intracranial involvement. Preoperative diagnosis can be challenging, and results from a small biopsy sample must be informed by multidisciplinary clinicoradiographic correlation. Preoperative planning is critical to success, with articulation of surgical goals and clear steps outlined for the approach. Good radiographic and clinical outcomes can be achieved surgically, particularly with awareness of the strategy of potentially leaving some small residual tumor at the margins to preserve nerve and muscular function. REFERENCES 1. Weiss SW, Goldblum JR. Enzinger and Weiss’ Soft Tissue Tumors, 5th ed. Philadelphia: Mosby Elsevier, 2008;917-919. 2. Perry A. Benign Triton tumour. In: Fletcher CDM, Bridge JA, Hogendoom PCW, Mertens F, eds. Pathology and Genetics of Tumours of Soft Tissue and Bone, 4th ed. Lyon, France: IARC Press, 2013; 185. World Health Organization Classification of Tumors, vol 5. 3. Amita K, Shankar SV, Nischal KC, Basavaraj HB. Benign triton tumor: a rare entity in head and neck region. Korean J Pathol 2013; 47:74-76. 4. Castro DE, Raghuram K, Phillips CD. Benign triton tumor of the trigeminal nerve. AJNR Am J Neuroradiol 2005;26:967-969. 5. Daley TD, Darling MR, Wehrli B. Benign Triton tumor of the tongue. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2008; 105:763-766. 6. Demir Y, Uluoglu O, Ozmen S, Boyacioglu ZM, Atabay K. Neuromuscular hamartoma in the mental region. J Oral Maxillofac Surg 2003;61:397^100. 7. Lena G, Dufour T, Gambarelli D, Chabrol B, Mancini J. Choristoma of the intracranial maxillary nerve in a child. Case report. J Neurosurg 1994;81:788-791. 8. O’Connell JX, Rosenberg AE. Multiple cutaneous neuromuscular choristomas: report of a case and a review of the literature. Am J Surg Pathol 1990;14:93-96. 9. Oeppen RS, Harden SP, Argent JD. Neuromuscular hamartoma: imaging features of a rare paediatric craniofacial tumour. Pediatr Radiol 2003;33:50-52. 10. Tiffee JC, Barnes EL. Neuromuscular hamartomas of the head and neck. Arch Otolaryngol Head Neck Surg 1998;124:212-216. 11. Tobias S, Kim CH, Sade B, Staugaitis SM, Lee JH. Neuromuscular hamartoma of the trigeminal nerve in an adult. Acta Neurochir (Wien) 2006;148:83-87.
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