Imaging of head and neck neoplasms in children
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- Robson, C.D. Pediatr Radiol (2010) 40: 499. doi:10.1007/s00247-009-1526-9
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The characteristic imaging appearance for a variety of common and/or important pediatric head and neck tumors will be described in this review. These include benign masses such as hemangioma, teratoma, nerve sheath tumors, juvenile nasopharyngeal angiofibroma and malignant masses such as rhabdomyosarcoma, lymphoma, carcinoma and retinoblastoma. This review focuses primarily on soft tissue tumors.
KeywordsPediatricsHead and neckTumorsHemangiomaTeratomaNerve sheath tumorJuvenile nasophayngeal angiofibromaLangerhans cell histiocytosisRhabdomyosarcomaCarcinoma
Imaging is commonly utilized to evaluate neoplasms of the head and neck in children. The most common benign tumor is hemangioma. Lymphoma (approximately 50% of cases) and rhabdomyosarcoma (approximately 20% of cases) account for the majority of malignant pediatric head and neck tumors [1, 2]. Thyroid, nasopharyngeal and salivary gland carcinomas are the most frequently encountered pediatric head and neck carcinomas. In this review article both typical and atypical appearances for the more commonly encountered primary, predominantly soft-tissue pediatric head and neck tumors will be described. Characteristic imaging findings that provide clues to a specific diagnosis will be emphasized as well as atypical appearances that should prompt an appropriate differential diagnosis. The typical appearance of some uncommon tumors will also be briefly discussed. In certain cases there are syndromic disorders or associations with which the reader should become familiar.
Important clinical features that should be taken into account when interpreting imaging include the age of the child, duration and nature of onset of the mass, location of the mass, characteristic imaging features (e.g., mineralization, vascularity, intensity of enhancement) and whether the child has a known mutation or syndrome associated with the development of neoplasms.
The choice of imaging modality depends on the nature and location of the tumor as well as proposed treatment options. US provides useful information in distinguishing cystic from solid lesions, detecting venous or arterial vascularity and differentiating nodal from non-nodal masses. CT is helpful in characterizing bony changes (remodeling, erosion, and sclerosis) and detecting intralesional calcification. CT is performed as helical axial images at 3-mm increments using a split dose bolus of contrast agent (half of the contrast bolus is administered, and images are then obtained after a 3-min pause during the administration of the 2nd half of the IV bolus). Reformatted sagittal and coronal images are then viewed with bone and soft-tissue reconstruction algorithms. As always, the lowest radiation dose should be used that can provide diagnostic-quality images while minimizing radiation dose to the child. MRI is the modality of choice for demonstrating the soft-tissue characteristics of tumors. The MR protocol should include multiplanar T1, fat-suppressed T2 or STIR images, a flow-sensitive gradient echo sequence, diffusion-weighted images (depending on suspected pathology) and gadolinium-enhanced, fat-suppressed T1-weighted sequences. Nuclear medicine studies including F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) and PET CT are useful for staging and follow-up of various tumor types, particularly lymphoma .
The acronym PHACES is used to describe the association of posterior fossa malformations, hemangiomas, arterial anomalies, coarctation of the aorta and cardiac defects, eye abnormalities, sternal malformations and supraumbilical raphe [5, 6]. The hemangiomas are typically large plaque-like or regional cutaneous hemangiomas involving the face, sometimes with a beard-like distribution or located in the midline of the head and neck . In our experience, the associated cerebellar malformations most commonly manifest as mild unilateral cerebellar hypoplasia. Absence or hypoplasia of the internal carotid or vertebral arteries and persistence of the trigeminal artery are the most common intracranial vascular anomalies associated with hemangioma. Progressive cerebrovascular occlusive changes have also been documented in patients with craniofacial hemangioma . Angiographically both aneurysmal and occlusive changes as well as vascular tortuosity occur.
Proliferating hemangiomas are well-circumscribed, solid and lobulated by US, CT and MRI (Fig. 1). High-flow vascularity is characteristic on US. Hemangiomas are isodense with muscle and enhance rapidly and intensely following the administration of contrast agent on CT (Fig. 1). On MRI, prominent vascularity appears as conspicuous flow voids on spin-echo pulse sequences and flow-related enhancement on gradient echo sequences. Proliferating hemangiomas are moderately hyperintense on T2-weighted images and enhance intensely. Involuting hemangiomas progressively shrink with increasing fibrofatty matrix, reduction in vascularity, and a relative decrease in enhancement (Fig. 1). The imaging features taken in conjunction with the age of the child usually permit a specific diagnosis to be made. Intraosseous lesions and small or involuting hemangiomas can be more difficult to diagnose as hemangioma with certainty. Pyogenic granuloma can simulate hemangioma clinically, but these lesions are usually superficial and cutaneous and are not generally imaged. Poorly defined or fuzzy margins are not typical of hemangioma and should prompt an alternative diagnosis such as kaposiform hemangioendothelioma. Other congenital tumors include rhabdomyoma, which demonstrates more homogeneous enhancement and lacks prominent vascularity, and infantile fibrosarcoma, which has more aggressive characteristics such as bony erosion, can be hemorrhagic and is sometimes somewhat vascular.
Hemangiomas are either treated expectantly, anticipating involution, or if interfering with vital functions accelerated involution is promoted by medical therapy with steroids, alpha interferon or more recently propranolol . Laser therapy is another therapeutic option for selected cases.
Teratoma is the most common congenital tumor of the head and neck, and this region is the second most common location for teratoma in early infancy. The WHO classification of germ cell tumors includes mature and immature teratoma and teratoma with malignant transformation. However, histological immaturity in congenital teratoma does not necessarily confer an adverse outcome, as is seen in adolescents and adults. Prenatal diagnosis of teratoma is made with fetal sonography or MRI. The tumor appears heterogeneous and sharply circumscribed with solid and cystic areas. Compression of the airway can occur and this finding will likely impact the timing and mode of delivery. When airway obstruction by tumor is diagnosed prenatally, the fetal exit procedure is preferred, with delivery of the baby by elective Caesarian section, and securing of the airway while the neonate remains on placental support. Midline teratoma that involves the oral cavity can be associated with cleft palate deformity. Infrahyoid teratoma frequently involves the thyroid gland and is considered by some to be of thyroid origin .
Nerve sheath tumors
Solitary neurofibromas and plexiform neurofibromas usually occur in children with neurofibromatosis (NF) type 1. Schwannomas occur sporadically in patients with NF2. Malignant peripheral nerve sheath tumor (MPNST) is usually seen in patients with NF1. Both solitary neurofibroma and schwannoma are sharply demarcated and of variable signal on T1- and T2-weighted images. Fibrous tissue in neurofibromas and Antoni A tissue in schwannomas contribute to marked T2 shortening that can simulate the high nuclear-to-cytoplasmic ratio of high-grade cellular neoplasms. These nerve sheath tumors typically enhance homogeneously but cystic foci can be seen in schwannomas. Plexiform neurofibromas tend to appear as sausage-shaped masses extending along peripheral nerves or nerve roots and sometimes located in multiple fascial compartments. They appear hypodense on CT and hyperintense on T2-weighted MRI and have a so-called target sign of central enhancement on CT and hypointensity on T2-weighted MR images that is characteristic of plexiform NF and helps distinguish this lesion from lymphatic malformations that also tend to involve multiple fascial compartments. MPNST is suggested by a rapid increase in size, alteration in enhancement characteristics or the development of metastatic disease. FDG PET imaging is of use for further evaluation of suspected MPNST.
Juvenile nasopharyngeal angiofibroma
Juvenile nasopharyngeal angiofibroma (JNA) is a relatively uncommon benign but locally aggressive neoplasm that predominantly affects adolescent boys, who typically present with epistaxis and nasal obstruction. JNA is a biphasic tumor that has both fibroblastic and vascular components. Although the etiology of JNA is unknown, a variety of growth factors (such as vascular endothelial growth factor), as well as chromosomal alterations are thought to play a role in its development and androgens have a role in tumor biology . JNA also has an increased frequency in patients with the familial adenomatous polyposis .
Langerhans cell histiocytosis
Langerhans cell histiocytosis (LCH) is an uncommon disease characterized by clonal proliferation of Langerhans cells together with other inflammatory cells and multinucleated giant cells. The latter cell is associated with the development of osteolysis. The exact etiology of LCH is uncertain; it might be neoplastic or linked to an initiating infectious, malignant or immune event . Clinical presentation and prognosis are variable, ranging from a solitary mass with an excellent prognosis to disseminated and sometimes fatal disease. LCH is one of the commonest causes of a solitary skull mass. The classic imaging appearance for LCH in the head and neck is a mass that produces “punched-out” lytic destruction of bone, and radiologic diagnosis in these cases is often straightforward. The soft-tissue component is sometimes focal and circumscribed, but borders can be tapered or even more diffuse, simulating an inflammatory lesion. Signal intensity on T2-weighted MR images is also variable. The lesions usually enhance homogeneously. Less commonly, foci of necrosis occur, simulating inflammation or more aggressive tumors. LCH can occur in any bone of the head and neck. Lesions within the temporal bone sometimes mimic cholesteatoma or aggressive infection. The demonstration of enhancing masses on MRI is useful in distinguishing LCH from other erosive processes within the temporal bone. The differential diagnosis for multiple osseous lesions includes metastatic disease. Solitary lesions that can simulate LCH include mastocytoma, juvenile xanthogranuloma and occasionally sarcomatous neoplasms.
Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma and the second most frequent head and neck malignancy after lymphoma [1, 2]. Approximately 36% of cases of RMS occur in the head and neck . The disease has a bimodal distribution with one peak occurring during the first decade of life and the second occurring during adolescence. The most common anatomic locations for RMS are the masticator space and orbit. RMS is typically an aggressive tumor that erodes bone. Parameningeal disease can accompany masticator space or nasopharyngeal tumors that extend through the central skull base. Metastatic cervical adenopathy is sometimes seen at the time of presentation. Presenting signs and symptoms include a neck mass, nasal obstruction with epistaxis, and proptosis. Large nasopharyngeal or oropharyngeal lesions tend to cause airway obstruction and obstruction of the ipsilateral eustachian tube with resultant otalgia.
Although most cases of RMS appear to be sporadic in nature, some young children (age <3 years) have identifiable constitutional mutations of the p53 tumor suppressor gene and a possible hereditary predisposition to cancer. The two most common histological types are embryonal and alveolar RMS. Embryonal RMS is more common in younger children and is sometimes associated with loss of heterozygosity of a portion of chromosome 11. In general the behavior, therapeutic response and prognosis of embryonal RMS is better than for alveolar RMS, which is seen in older children. More recently molecular criteria for RMS based on genomic analysis have been described, with potential prognostic and therapeutic significance . Approximately 55–75% of alveolar RMS cases have a FOX01 to PAX3 or PAX7 fusion. Alveolar RMS that lacks this translocation tends to behave in a fashion more similar to embryonal RMS.
Treatment of RMS involves surgery, radiation, and chemotherapy. Post-treatment resolution of tumor is a good indicator of prognosis, but disease can recur, and serial scans are usually obtained to detect early disease recurrence. The prognosis depends on histological and molecular subtype and is better for localized disease and complete surgical resection.
Lymphoma is the most common head and neck malignancy in children. Hodgkin lymphoma (HL) occurs primarily in early adolescence and is more common than non-Hodgkin lymphoma (NHL), which occurs throughout childhood . HL manifests as nodal disease with a firm, non-tender unilateral neck mass, or less commonly bilateral neck masses, with disease involving contiguous lymph nodes. Constitutional symptoms are also sometimes present and usually indicate generalized disease. Associated mediastinal involvement is seen in approximately 40% of HL patients, and 80% of patients with cervical HL have disease outside of the head and neck . HL is characterized by Reed-Sternberg cells, which are giant multinucleated lymphocytes with eosinophilic nucleoli. The predominant histological subtype of HL is nodular sclerosing. Various etiologies have been implicated, including prior infection with the Epstein-Barr virus (EBV).
NHL presents as painless unilateral adenopathy. Approximately 30% of cases present with extranodal disease in the head and neck, and approximately 70% of patients have disease outside of the head and neck . Extranodal NHL disease involves the lymphoid tissue of the Waldeyer ring, or the sinonasal, thyroid or orbital regions. Histological subtypes of NHL in children include Burkitt lymphoma, lymphoblastic lymphoma, diffuse large B-cell lymphoma, and anaplastic large cell lymphoma. Although the exact etiology and pathogenesis of NHL is unknown, predisposing factors include severe immunocompromise, especially when associated with certain infectious agents such as EBV, and exposure to oncogenic infections or environmental carcinogens while in an immuncompromised state . Increased incidence of NHL is seen in children with hereditary immunodeficiencies. In immunosuppressed children the development of lymphoproliferative disorders including lymphoma is thought to be multifactorial, related to both immunosuppressant therapy and ongoing antigenic stimulation. Infectious agents associated with NHL include human immunodeficiency virus, EBV, human T-cell lymphotropic virus-1, human herpes virus 8, Helicobacter pylori and Chlamydia psittaci . EBV is also implicated in the pathogenesis of Burkitt lymphoma.
The most frequently encountered carcinomas of the head and neck are thyroid carcinoma and nasopharyngeal carcinoma (NPC). Thyroid carcinoma presents as a thyroid mass with or without cervical adenopathy. The most common histological subtype is papillary carcinoma. Papillary carcinoma occasionally arises in association with a thyroglossal duct cyst, manifesting as a calcified mural nodule, an entity that is more typically encountered in adults.
Nuclear protein in testis (NUT) midline carcinoma is a rare, distinctive and highly lethal tumor characterized by a unique chromosomal rearrangement involving the NUT gene on chromosome 15 . This cytogenetic abnormality is a harbinger of a poor prognosis and generally death occurs in months because of metastatic disease in spite of aggressive treatment. In the head and neck these tumors involve the sinonasal region, the epiglottis or larynx . The signal intensity on T2-weighted MR images is consistent with a cellular neoplasm; however, imaging characteristics are otherwise indistinguishable from other high-grade neoplasms such as lymphoma or sarcoma that are also associated with aggressive bone destruction and metastatic adenopathy.
Carcinoma involving the salivary glands is most frequently mucoepidermoid in nature. These tumors can be difficult to distinguish based on imaging from other parotid tumors, the most common of which is pleomorphic adenoma. The signal and enhancement characteristics of mucoepidermoid carcinoma are variable, as is the histological grade.
Retinoblastoma (RB) is the commonest ocular malignancy in children. The peak incidence is in the first 3 years of life. The typical clinical presentation of RB is leukocoria and sometimes strabismus. Fundoscopy reveals a whitish tumor, sometimes with satellite lesions in the retina, subretinal space and vitreous. Retinal detachment can also occur. Up to 30% of cases are bilateral . Bilateral cases tend to present at an earlier age and disease is sometimes multifocal. Bilateral RB is associated with mutations in the RB1 gene located in chromosome 13q . Although the chromosomal abnormality frequently arises as a de novo mutation, familial cases also occur. RB is thought to be initiated by inactivation of the tumor suppressor RB1 gene or other genes in that pathway. Children with bilateral RB have a significant predisposition to the development of other tumors such as osteogenic sarcoma, both related and unrelated to prior irradiation.
Children with unilateral RB usually undergo surgical enucleation. Bilateral RB is often treated with a combination of chemotherapy and focal radiotherapy to the globe.
Metastatic disease involving the pediatric head and neck most commonly involves the bony skeleton with variable involvement of cervical lymph nodes. During the first decade of life, especially in children younger than 2 years, neuroblastoma is most common. Leukemic disease is also common, usually in older patients, and sometimes indistinguishable in imaging appearance. Solitary and multiple facial and calvarial masses can also occur as a manifestation of metastatic disease caused by a wide variety of other tumor types, often sarcomatous, usually in older children. Clinical presentation occurs when metastases of the head and neck are discovered at the time of tumor staging, or alternately when the first presentation is with metastatic disease that produces proptsosis with orbital, facial bone and calvarial masses. CT demonstrates lytic, permeative bony destruction, spicculated periosteal reaction and enhancing soft-tissue masses. On MRI, masses are of relatively low signal on T2-weighted images with moderate to intense enhancement. Neuroblastoma sometimes produces diffuse expansion of the diploic space because of marrow involvement.