Congenital and developmental masses

Branchial cleft cysts

Branchial cleft abnormalities are usually diagnosed in childhood due to recurrent infection[1].They are either simple branchial cleft cyst (BCC), or have fistulas which increases the risk of superinfection[2]. Second BCCs are the most common. They occur anywhere from the palatine tonsil to the supraclavicular neck. Third and fourth BCCs occur in the lower lateral neck[3].

• On CT imaging BCCs demonstrate cystic appearance, hypoattenuating on CT with thin non-enhancing wall (Fig 1). If infected, they show thickened wall with significant enhancement, and inflammatory changes of surrounding tissue.
• On MRI they appear as cystic structures of high signal on T2 weighted imaging but T1 appearances alters with proteinaceous contents.
  

  Fig 1: Branchial cleft cyst. Axial (A) and recontructed sagittal (B) contrast-enhanced CT images show a unilocular low density collection anterior to right submandibullary gland. There is slight rim enhancement following contrast application (arrow).

Lymphangioma

Lymphangiomas or cystic hygromas, are cystic masses composed of abnormal lymphatic tissue, filled with protein rich fluid. In the suprahyoid neck they occupy the masticator or submandibular spaces, whereas in the infrahyoid neck they are located in the posterior cervical space. Large lymphangiomas occupy more than one space, insinuating between normal structures[3].  Lymphangiomas may be macrocystic, microcystic or mixed cystic. 

• On CT they usually appear as homogenous hypodense cystic lesions with multiple thin, irregular septations.
• On MRI they have low signal intensity on T1 weighted and high on T2 weighted images, though the signal may vary depending on the protein content and the presence of blood products(Fig 2.). Upon contrast adminitration, the cyst walls and septas will enhance, but the content within the cystic space does not enhance.
  

  Fig 2: Lymphangioma. Coronal T1WI (A) and fat-suppressed T2WI (B) demonstrate multilocular, trans-spatial cystic mass (arrow), with low T1 intensity and hyperintense signal on fat-suppressed T2 sequences.

Infectious and inflammatory conditions

Lymphadenitis

Cervical lymphadenitis is by far the most common cause of neck masses in children [1].

Viral adenitis is bilateral. Acute unilateral lymph node enlargement may indicate bacterial infection[4]. Lymphadenitis can present as isolated nodes or in conglomerates.

• Reactive lymph nodes are usually enlarged and may show slight postcontrast enhancement on CT or MRI. (Fig 3.).
  

  Fig 3: Lymphadenitis. Axial (A) and reconstructed sagittal (B) contrast enhanced CT images demonstrate multiple enlarged lymph nodes bilaterally. Areas of central low density on sagittal image (white arrowhead) represents area of necrosis.

Parotid gland abscess

The most common cause of acute bacterial parotitis and neck abscesses in adults, and in pediatrics population is Staphylococcus aureus [5].

CT is useful for detection of deep neck infections, providing information about the location and anatomic relations of the abscess.

• On CT, abscess appears as hypodense collection with a complete postcontrast peripheral rim enhancement. Adjacent lymphadenopathy and inflamatory changes of surrounding soft tissue is seen (Fig 4.).
• Multiplanar MRI sequences allow more accurate delineation of the process. There is central hypo-intensity on T1 and hyper-intensity on T2, with peripheral enhancement.
  

  Fig 4: Parotid gland abscess. Axial contrast-enhanced CT image show an irregular low-density collection with thick rim enhancement, adjacent to the left sternocleidomastoid muscle, extending from the lower parts of left parotid gland (arrow). Enlarged lymph nodes are seen around the abscess, as well as fat stranding, suggesting reactive changes of the surrounding tissue.

Neoplastic masses

Hemangioma

Infantile haemangiomas (IH) are benign vascular neoplasms, composed of vascular channels lined by normal endothelial tissues. They are the most common tumor of the head and neck in infancy[6].

Hemangiomas display proliferation phase during the first year of life followed by an involution phase with gradual regression during up to 10 years [2].

• On CT, proliferating hemangiomas appear as lobulated solid tumors isodense with muscle. They enhance rapidly and demonastrate rapid washout. In involution phase, they may contain areas of fat density.
• On MR, they have appearance of a lobulated mass, isointense to muscle on T1 and moderately hyperintense with flow voids on T2. They demonstrate robust enhancement (Fig 5.). However, involuting hemangiomas on MR are characterized by increased heterogeneity on both T1 and T2, due to accumulation of fatty tissue, as well as decreae of fast-flow vascularity, and variable enhancement [7].
  

  Fig 5: Hemangioma. Sagittal T2WI-FS (A) image shows an extensive T2 hyperintense lesion with discrete internal septa and flow voids (arrows). Prominent contrast enhancement is seen on coronal post-contrast T1WI (B).

Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is regarded as a reactive clonal disease of the monocyte-macrophage system [8]. The radiologic presentations of LCH range from lytic skeletal lesions to widespread disease with severe organ dysfunction.

• On CT it is seen as circumscribed rounded lytic lesions of the calvarium. Associated enhancing soft tissue mass may be present (Fig 6.).
• On MRI, the skull lesions on T1 weighted images are typically hypo- to isointense, with intermediate-to-high signal on T2 weighted images and high signal on fat suppressed sequences. They show postcontrast enhancement, and may display diffusion restriction, which can be seen in malignant lesions.
  

  Fig 6: Langerhans cell histiocytosis. Axial non-contrast CT images with soft tissue (A) and bone (B) window show lytic lesions of right zygomatic arch (arrows) and sphenoid bone wings on the left side (white arrowhead). Soft tissue masses are seen in these areas (black arrowhead).

Nasopharyngeal carcinoma

Nasopharyngeal carcinomas (NPC) are the most prevalent primary cancers of the nasopharynx. They are of squamous cell origin. The childhood type is strongly associated with Epstein-Barr virus infection [9]. NPC are usually asymetric, typically arising in the Fossa of Rosenmuller.

• On CT NPSs appear as soft tissue masses which demonstrate heterogenous enhancement following administration of contrast. It is important to evaluate cervical lymph nodes due to the high rate of nodal involvement.
• On MRI they are usually slightly hyperintense on T1 weighted images and moderately hyperintense on T2 weighted images, with postcontrast enhancement (Fig 7.). Invasion of surrounding neck spaces are common in pediatric patients. MR is important in evaluating perineural spread of NPC.
  

  Fig 7: Nasopharyngeal carcinoma. Axial T1WI (A), T2WI (B), post-contrast T1WI (C) and fat suppressed sequence (D) show an irregular mass in the right fossa Rossenmuller (arrows). Heterogenous enhancement is seen following contrast application (C).

Schwannoma

Schwannomas are benign tumors of Schwann cell origin and are the most common tumor of peripheral nerves. MRI should be considered the imaging modality of choice for evaluating the associated nerve of origin [10].

• On noncontrast CT schwannomas show low to intermediate with intense postcontrast enhancement. Larger tumors may exhibit heterogeneous enhancement. Adjacent bone remodeling may be seen.
• On MR imaging schwannomas are ovoid or fusiform masses typically hypo- to isointense on T1 weighted images, showing intense postcontrast enhancement. On T2 they are usually heterogeneously hyperintense, with possible cystic areas and areas of hemosiderin in larger tumors (Fig 8.).
  

  Fig 8: Schwannoma. Coronal T1WI (A), T2WI (B), coronal fat–suppressed T2 (C) and axiall post-contrast T1 images show well-defined T2 hyperintense, homogeneously enhancing mass in the right submandibular area (arrows).

Acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a cancerous condition of the bone marrow marked by the abnormal growth of lymphoid progenitor cells. While imaging is not diagnostic, it should be considered as part of the differential diagnosis when evaluating patients with other non-specific symptoms. [11].

• On CT affected lymph nodes are enlarged, rounded or irregular in shape. They show homogeneous or heterogeneous postcontrast enhancement, depending on the presence of necrosis or other pathological changes. Lymphadenopathy can affect cervical, mediastinal, axillary, and abdominal lymph nodes (Fig 9.).
• On MRI enlarged lymph nodes may appear hypointense on T1-weighted images, hyperintense on T2-weighted images. They may show intense postcontrast enhancement. Areas of necrosis appear as central low-signal regions on T2-weighted images.
  

  Fig 9: Acute lymphoblastic leukemia. Contrast enhanced axiall (A) and coronal (B) CT images demonstrate enlarged homogenously enhancing nodes in the neck (arrows), extending towards the upper mediastinum (white arrowhead). There is a necrotic node adjacent to left sternocleidomastoid muscle (black arrowhead) seen on the axiall scan.

Hodgkin's lymphoma

Lymphomas are the most common malignant tumors of the head and neck region in children. Hodgkin's lymphoma tends to affect the internal jugular chain lymph nodes extending to the superior mediastinal nodes. It can also affect the spleen, lungs, bone, bone marrow and rarely liver. Non-Hodgkin lymphoma (NHL) more commonly demonstrates extranodal disease[2].

• On CT affected lymph nodes are round, enlarged, homogenous and isodense to muscle. Enlarged nodes may show homogeneous postcontrast enhancement (Fig 10.). Calcifications may bee seen following radiation therapy.
• On MR imaging enlarged nodes are usually isointense on T1 weighted images and hyperintense on T2-weighted imaging. On postcontrast images they demonstrate variable, usually mild, homogenous enhancement.
  

  Fig 10: Hodgkin's lymphoma. Coronal postcontrast CT shows bulky homogenously enhancing nodes of the neck and mediastinum (arrows).

Neuroblastoma

Neuroblastoma is a subtype of rare primitive neuroectodermal tumors (PNETs)[6]. It may occur anywhere along the sympathetic chain. Imaging usually reveals a soft tissue mass that may merge with adjacent lymph nodes.

• On CT the tumor typically appears heterogeneous with calcifications, sometimes with internal areas of hemorrhage or necrosis.
• MRI usually demonstrates low signal on T1 and high heterogenous signal on T2 weighted imaging with cystic or necrotic areas. Following contrast application, heterogeneous enhancement is seen (Fig 11.).
  

  Fig 11: Neuroblastoma. Coronal T1WI(A), sagittal fat-suppressed T2 (B), and contrast-enhanced axiall (C) and coronal (D) T1WI demonstrate a heterogeneously enhancing solid lower cervical soft tissue mass that extends to the upper mediastinum (arrows).

Epithelioid sarcoma

Epithelioid sarcoma (ES) is a rare slow-growing mesenchymal tumor, usually located in the extremities, and exceptionally in the neck area [12].

• On CT ES shows lobulated or contours and sometimes peripheral calcifications[13].
• On MR it exibits heterogeneous patterns due to varying amounts of necrosis, hemorrhage, and granulomatous areas. Signal intensity on T1 and T2 weighted images is variable. On T2 it may be iso to hyperintense compared to muscles. The tumor shows heterogenous postcontrast enhancement (Fig 12.).
  

  Fig 12: Epithelioid sarcoma. Axiall T2WI (A), sagittal T2WI (B), fat-suppressed T2 (D), and contrast enhanced T1WI (C) demonstrate irregular soft tissue mass with heterogenous post-contrast enhancement, extending from the clivus towards the retropharyngeal space.