Pediatric Radiology

, Volume 40, Issue 4, pp 499–509

Imaging of head and neck neoplasms in children

Authors

    • Department of RadiologyChildren’s Hospital Boston
Review

DOI: 10.1007/s00247-009-1526-9

Cite this article as:
Robson, C.D. Pediatr Radiol (2010) 40: 499. doi:10.1007/s00247-009-1526-9

Abstract

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.

Keywords

PediatricsHead and neckTumorsHemangiomaTeratomaNerve sheath tumorJuvenile nasophayngeal angiofibromaLangerhans cell histiocytosisRhabdomyosarcomaCarcinoma

Introduction

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 [3].

Hemangioma

Hemangioma is the most common vascular tumor, arises in infants, and is more common in girls. Hemangiomas proliferate with rapid growth during the first year of life, followed by involution with slow regression during the ensuing several years. During the proliferating phase, hemangiomas display prominent vascularity. Involution is characterized by decreased vascularity and shrinkage of the mass with an increasing proportion of fibrofatty matrix. Rare true congenital hemangioma proliferates in utero, is fully developed at birth and typically has an accelerated course, sometimes involuting completely during the first year of life (Fig. 1). Those that involute completely are termed RICH (rapidly involuting congenital hemangioma) as opposed to those that do not involute completely, which are termed NICH (noninvoluting congenital hemangioma). Approximately 20% of children have multiple hemangiomas. Hemangiomas are most prevalent in the head and neck region. Cutaneous involvement produces a characteristic raised, bosselated, crimson-colored mass or alternatively a more macular appearance that must be distinguished from the capillary malformation or port wine stain [4]. Complications of hemangiomas include cosmetic deformity, mass effect, interference with vital functions, ulceration and bleeding.
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Fig. 1

Hemangioma. a Fetal US with power Doppler at 30 weeks’ gestation reveals a very vascular scalp mass. b Single-shot fast spin-echo T2-weighted coronal MR in the same patient shows the mass (arrow), which is isointense to white matter and contains signal voids (arrowheads) caused by prominent vessels. c Axial contrast-enhanced CT in 3-month-old boy demonstrates an intensely enhancing, sharply demarcated and lobulated parotid hemangioma (arrow). d Axial contrast-enhanced CT in a 6-year-old girl with an involuting hemangioma shows faintly enhancing residual hemangioma (arrows) with interspersed fibrofatty tissue (arrowhead). e Axial T2-W STIR MR image in a 4-month-old girl demonstrates a parotid hemangioma (arrow) that is isointense with reactive cervical nodes. Prominent high-flow vascular flow voids are seen. f Axial gadolinium-enhanced T1-weighted fat-suppressed MRI of the same hemangioma (arrow) demonstrates intense enhancement

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 [7]. 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 [8]. 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 [9]. Laser therapy is another therapeutic option for selected cases.

Teratoma

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 [10].

CT of teratoma demonstrates a heterogeneous solid and cystic mass with specks of calcification (Fig. 2) and sometimes fatty tissue. The fatty tissue is well appreciated with CT and MRI. The soft-tissue components of tumor other than fat demonstrate enhancement. The differential diagnosis for predominantly cystic teratoma is primarily lymphatic malformation and occasionally infantile myofibromatosis. The presence of irregular calcific densities and apparent origin of the tumor from the thyroid gland with absence of the ipsilateral thyroid lobe or splaying of thyroid tissue around the periphery tumor are useful features that help distinguish teratoma from lymphatic malformations (Fig. 2). Other head and neck tumors that have fatty tissue include lipoma (homogeneous fatty tissue) and lipoblastoma (fatty component and soft-tissue component). The most common calcified tumor in the head and neck is pilomatrixoma, which is a small calcified cutaneous and subcutaneous tumor. Less common congenital solid tumors include rhabdomyoma and congenital infantile fibrosarcoma, as mentioned earlier.
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Fig. 2

Teratoma. a Sagittal reformatted contrast-enhanced CT of the neck in a 5-day-old boy demonstrates a large, heterogeneous, cystic and solid cervical teratoma with flecks of calcification (arrows). The calcifications and solid elements distinguish the tumor from a lymphatic malformation. b Axial gadolinium-enhanced T1-weighted fat-suppressed MR image in a 1-day-old intubated boy with a right cervical teratoma (long arrow). Note the left lobe of the thyroid gland (arrowhead). Right thyroid tissue appears draped around the periphery of the tumor (short arrows), suggestive of thyroid origin of the mass, which is typical of infrahyoid cervical teratomas

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 [11]. JNA also has an increased frequency in patients with the familial adenomatous polyposis [12].

JNA arises along the posterolateral wall of the nasal cavity, spreads to involve the ipsilateral nasal cavity, and characteristically grows laterally into the pterygopalatine fossa (Fig. 3). The locally aggressive behavior manifests as erosion and bowing of the contiguous bone of the paranasal sinuses, orbits and skull base, permitting paranasal sinus, intraorbital and intracranial extension with cavernous sinus involvement. Tumor that obstructs the paranasal sinuses results in trapped secretions, which must be distinguished from tumor so as not to overestimate the extent of tumor. On plain films JNA produces characteristic anterior bowing of the posterior wall of the maxillary antrum. Bony remodeling and destruction is well-demonstrated with CT (Fig. 3). MR reveals a lobulated tumor of variable signal intensity on T2-weighted MR images, often appearing relatively hypointense because of fibrous tissue (Fig. 3). Prominent vascularity is seen as flow voids within the tumor, with intense enhancement on both CT and MR images (Fig. 3). Angiography demonstrates an intense tumor blush with enlarged arterial supply via branches of the internal maxillary, ascending pharyngeal and palatine arteries (Fig. 3). The anastamotic connections between the internal and external carotid arteries are also frequently enlarged, and this has to be taken into account when performing preoperative embolization. The characteristic age, clinical presentation and imaging features usually permit a confident preoperative diagnosis of JNA. Occasionally, observed atypical features include the occurrence of JNA in preadolescent boys and lack of characteristic growth into the pterygopalatine fossa. In other cases preadolescent age and a lack of the typical angiographic tumor blush have prompted a differential diagnosis with histological examination subsequently demonstrating rhabdomyosarcoma or spindle cell sarcoma. The pattern of bony destruction and lack of prominent vascularity are key features in distinguishing sarcomatous tumors, lymphoma and carcinoma from JNA.
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Fig. 3

JNA in an 18-year-old boy with epistaxis. a Axial contrast-enhanced CT shows a large, avidly enhancing tumor obstructing the right nasal cavity and nasopharynx and extending into the right maxillary antrum, sphenoid sinus and pterygopalatine fossa (arrow). b Bone windows reveal extensive bony destruction of the right maxillary antrum (arrowhead), right pterygoid plates (arrow) and central skull base. c Axial fat-suppressed T2-weighted image demonstrates heterogeneous tumor signal with hypointense foci (arrow). d Coronal gadolinium-enhanced T1-weighted fat-suppressed MR image shows intense enhancement of the tumor and prominent arterial flow voids (arrow). e Carotid angiography with selective injection of the right external carotid artery demonstrates arterial supply from the internal maxillary artery branches (arrow) with an intense tumor blush (arrowheads)

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 [13]. 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

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 [14]. 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 [15]. 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.

Imaging of RMS shows a soft-tissue tumor, often with lytic bone destruction or occasionally bony remodeling (Fig. 4). The tumor is usually heterogeneous, sometimes necrotic, and has relatively well-circumscribed borders. On contrast-enhanced CT or MRI variable tumor enhancement is observed. The signal intensity of tumors on T2-weighted images is variable but usually relatively iso- to hypointense compared with brain due to the cellular nature of the tumor (Fig. 4). Coronal contrast-enhanced fat-suppressed T1-weighted images are very useful for the detection of parameningeal tumor. A survey of the cervical lymph node chain should also be performed to detect metastatic adenopathy. Atypical or unusual features of RMS include marked hyperintensity on T2-weighted images and intratumoral hemorrhage. The differential diagnoses for RMS depend on the location of tumor and include lymphoma, carcinoma (teenagers), other types of sarcoma, JNA (especially in adolescent boys with nosebleeds) and desmoid tumor. Osteogenic sarcoma (OSA) or Ewing sarcoma is suggested by a tumor that primarily involves bone and is characterized by a proliferative periosteal reaction and soft-tissue mass. OSA can arise spontaneously or as a complication of radiation therapy. Other sarcomas that arise in the head and neck include fibrosarcoma, chondrosarcoma and synovial sarcoma.
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Fig. 4

Rhabdomyosarcoma in a 17-year-old boy with restricted jaw mobility. a Axial T2-weighted MR image shows a hypointense tumor (arrow) within the right masticator space. b Axial CT image shows the mass (long arrow) with erosion of the right mandibular ramus and posterolateral wall of the right maxillary antrum (short arrows). c A more cephalad CT image reveals enlargement of the right foramen ovale compared with the left (arrowheads) caused by extension of tumor. There is opacification of right mastoid air cells from eustachian tube obstruction as a result of the tumor

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

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 [1]. 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 [1]. 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 [1]. 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 [16]. 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 [16]. EBV is also implicated in the pathogenesis of Burkitt lymphoma.

Doppler US can be helpful in distinguishing reactive from malignant adenopathy. Features of malignant nodes include displacement of vessels, which correlates with perinodal tumor spread, aberrant vessels, avascular foci and subcapsular vessels [17]. On CT, involved nodal tissue typically does not enhance as avidly as infectious lymphadenitis, and stranding of the surrounding fat is usually absent (Fig. 5). The presence of a soft-tissue mass with bony involvement of the mandible and “floating teeth” is characteristic of but not specific for Burkitt lymphoma. On MRI, lymphomatous involvement tends to produce enlargement of lymphoid tissue that is often homogeneous and of lower signal intensity than reactive adenopathy (Fig. 5), with variable enhancement that is less marked than reactive adenopathy. Whole-body imaging for diagnosis, staging and follow-up of disease can be performed using nuclear medicine imaging with F-18 FDG PET [18]. In a study comparing FDG PET with CT, MRI, and gallium scans, FDG PET had higher sensitivity and specificity than the other imaging modalities for pediatric HL and NHL [19]. The differential diagnoses include infectious or inflammatory disease (especially EBV infection), other lymphoproliferative disorders such as Castleman disease, and massive sinus histiocytosis and metastatic adenopathy.
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Fig. 5

Lymphoma. a HL in a 16-year-old boy with lymphadenopathy. Reformatted coronal contrast-enhanced CT of the neck reveals left greater than right cervical and anterior mediastinal adenopathy (arrows). b FDG PET in the same boy shows multiple sites of FDG-avid disease, including a large mass in the anterior mediastinum and numerous enlarged lymph nodes in the mediastinum, neck and right hilum (arrows). c Burkitt lymphoma in an 8-year-old boy with constitutional symptoms and a sore throat. Axial contrast-enhanced CT shows a large minimally enhancing mass involving the right tonsil (arrows) with mass effect on the oropharynx. d Axial fat-suppressed T2-weighted MR image in the same patient shows that the tumor is homogeneous and hypointense—characteristic of lymphoma

Carcinoma

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.

NPC occurs in adolescents. Presenting symptoms and signs include a nasopharyngeal mass, cervical lymphadenopathy, unilateral otitis media, rhinorrhea and nasal obstruction. NPC is related to prior EBV infection. On imaging NPC manifests as a nasopharyngeal mass with cervical lymphadenopathy and aggressive characteristics including bony destruction of the paranasal sinuses and central skull base and intracranial extension (Fig. 6). The differential diagnosis based on location is lymphoma.
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Fig. 6

EBV-associated nasopharyngeal carcinoma in a 19-year-old man with neck pain, left facial numbness and otalgia. a Axial T2-W STIR MR image shows a heterogeneous, hypointense tumor within the left nasopharynx (long arrow), eroding the clivus. There is an enlarged right retropharyngeal lymph node(short arrow). There is fluid signal within left mastoid air cells (arrowhead) because of eustachian tube obstruction by the tumor. b Coronal gadolinium-enhanced T1-weighted fat-suppressed MR image shows homogeneously enhancing tumor within the nasopharynx, extending through the foramen ovale (arrowhead) into the cavernous sinus and obliterating the left internal carotid artery. There is an epidural component within the left middle cranial fossa (arrow)

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 [20]. 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 [21]. 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

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 [22]. 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 [23]. 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.

RB must be differentiated from benign causes of leukocoria such as infection (Toxocara canis), PHPV, and Coats disease. US and CT of RB reveal an intraocular calcified mass, sometimes with associated retinal detachment (Fig. 7). Usually the globe is normal in size or enlarged, which helps distinguish RB from other calcified lesions such as prior infection or retinopathy of prematurity. MRI is usually reserved for cases of bilateral retinoblastoma for evaluating for suspected extraocular extension and for the development of synchronous or metachronous tumors in the hypothalamic and pineal regions as well as surveillance for other tumors such as osteogenic sarcoma.
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Fig. 7

Retinoblastoma. a Image in a 4-year-old boy with decreased left visual acuity who was found to have a white intraocular tumor with vitreous seeding and associated retinal detachment. Axial contrast-enhanced CT shows the calcified tumor (arrow) involving the left globe with a retinal detachment (arrowhead). b Image of a 4-month-old boy noted by his father to have a white reflex in the right eye and found to have bilateral retinoblastoma. Axial T2-W STIR MR image shows bilateral hypointense retinoblastoma (arrows). The boy was found to have chromosome 13q deletion

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

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.

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