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Nasopharyngeal carcinomas

Nasopharyngeal carcinoma (NPC) is the most common primary malignancy of the nasopharynx, with late clinical presentation after significant tumor growth and adjacent structure invasion. Imaging is essential for staging, detecting local extension and nodal metastases which are present in 75-90% of patients at diagnosis.

Key Images

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Look For First
  • Mass centered at fossa of Rosenmüller, the most common site of origin for nasopharyngeal carcinoma
  • Cervical lymph node involvement, particularly retropharyngeal and level II nodes present in 75-90% of patients at diagnosis
  • Evidence of bone destruction at skull base, particularly through foramen lacerum, foramen ovale, or clivus indicating aggressive disease
Key Image Findings
  • CT: Nasopharyngeal carcinomas appear as soft tissue masses most commonly centered at the fossa of Rosenmüller with heterogeneous enhancement following contrast administration.
  • CT: Small lesions confined to the nasopharynx are indistinguishable from prominent adenoidal tissue, but larger aggressive tumors erode the base of skull with irregular bone margins characteristic of destructive processes.
  • CT: The tumor may extend through the Eustachian tube, foramen lacerum, foramen ovale, or directly through bone into the clivus, cavernous sinus, and temporal bone.
  • MRI T1: Tumor is typically isointense to muscle, aiding visualization against normal nasopharyngeal anatomy.
  • MRI T2: Tumor is isointense to somewhat hyperintense to muscle; fat saturation sequences are helpful for delineating soft tissue extent.
  • MRI post-contrast (fat-saturated): Prominent heterogeneous enhancement is typical, with careful assessment for perineural spread which is a key advantage of MRI over CT.
  • MRI diagnostic criteria include mucosal asymmetry, loss of adenoidal septa, and loss of integrity of the deep mucosal white line on well-selected patient cohorts.
  • MRI is superior for detecting intracranial extension and bone marrow infiltration changes of the clivus, though not all marrow changes represent true tumor extension.
Differential Diagnosis
  • Prominent normal adenoidal tissue: has a characteristic striped appearance on MRI T1WI and T2WI and is typically symmetric without mass effect
  • Nasopharyngeal lymphoma: may present as mucosal or mass lesion but lacks the asymmetry and nodal pattern typical of carcinoma
  • Adenoid cystic carcinoma: tends to have perineural spread but different histology and slower growth pattern than squamous cell carcinoma
  • Chordoma: arises from clivus and typically has specific location and bone destruction pattern that differs from carcinoma origin at fossa of Rosenmüller
  • Juvenile nasopharyngeal angiofibroma (JNA): occurs in younger males, highly vascular on imaging with different enhancement pattern and typically in nasal cavity
  • Skull base tumors (meningioma, chondrosarcoma, plasmacytoma, pituitary adenoma): distinguished by their specific locations, bone involvement patterns, and origin sites rather than mucosal origin
Discussion

Nasopharyngeal carcinoma is strongly associated with Epstein-Barr virus (EBV) in non-keratinizing and basaloid subtypes, particularly in Asian populations, whereas keratinizing type shares risk factors of smoking and alcohol common to other head and neck squamous cell carcinomas.

Clinical presentation is often delayed until advanced stage because early symptoms (nasal obstruction, epistaxis, conductive hearing loss from Eustachian tube obstruction) are overlooked, leading to high rates of nodal metastases and distant spread at diagnosis.

Retropharyngeal nodes are usually the first nodes involved, but in up to 35% of cases these nodes are skipped and level II nodes are involved first, requiring careful assessment of the entire cervical lymph node chain.

MRI is the modality of choice for staging due to superior soft tissue resolution and sensitivity for perineural spread and intracranial extension, whereas CT is ideal for early detection of bony skull base involvement.

Post-radiotherapy fibrosis can be distinguished from residual or recurrent tumor on MRI only when mature (low T2 signal, no enhancement), but early fibrotic change cannot be reliably distinguished and may require follow-up imaging or PET.

F-18 FDG-PET is highly sensitive for detecting nodal metastases and recurrent disease and is the modality of choice for surveillance after treatment.

Reporting Pearls

Clearly identify the tumor's origin at the fossa of Rosenmüller and describe the pattern and extent of skull base involvement (specify which foramina or bone structures are affected), lymph node levels involved (particularly status of retropharyngeal and level II nodes), and presence or absence of perineural spread and intracranial extension, as these findings directly impact TNM staging and treatment planning.

Pitfalls
  • Mistaking prominent normal adenoidal tissue for carcinoma, particularly in smaller lesions confined to the nasopharynx; look for the characteristic striped MRI appearance and symmetry of normal adenoids
  • Missing cervical lymph node involvement by inadequately assessing the entire node chain, especially retropharyngeal and level II nodes which are most commonly affected
  • Confusing post-radiotherapy fibrosis with residual or recurrent tumor on CT; mature fibrosis is low signal on T2 and non-enhancing on MRI, whereas early changes cannot be reliably distinguished without clinical correlation or follow-up
  • Overlooking bone marrow signal changes on MRI of the clivus as not all marrow changes represent tumor infiltration; correlation with structural bone destruction on CT is essential for accurate staging
Source: Reference source

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