Pre-treatment and post-treatment nasopharyngeal carcinoma imaging: imaging updates, pearls and pitfalls

Abstract

Purpose: Nasopharyngeal carcinoma (NPC) is endemic in Southeast Asia, requiring precise imaging for personalized treatment. This review highlights key imaging challenges and updates from recent literature, emphasizing findings that impact oncological management.

Methods: We discuss common and uncommon clinical entities, detailing salient imaging features and diagnostic distinctions to aid accurate interpretation.

Results: In the pre-treatment setting, leveraging the characteristic MR signals and spread patterns of NPC aids in defining the tumor volume for accurate staging and radiotherapy contouring. Key diagnostic challenges include differentiating tumor from benign hyperplasia, skull base osteomyelitis, and other skull base tumors. Perineural tumor spread, radiological extranodal extension and nodal necrosis further refine primary tumor and nodal assessment. In the post-treatment setting, the key question is whether tumor recurrence exists. Diagnostic challenges involve distinguishing tumor recurrence from scar tissue, post-radiation nasopharyngeal necrosis, or hypertrophied cervical ganglia. For recurrences, endoscopic nasopharyngectomy has emerged as the preferred approach over open surgery or re-irradiation. The text highlights characteristic post-treatment appearances and emphasizes recognizing these patterns to avoid misinterpretation and guide appropriate management.

Conclusion: Imaging plays a pivotal role in NPC precision oncology. Mastering imaging pearls and pitfalls empowers radiologists to provide clinicians with reliable, actionable guidance.

Keywords: Computed tomography; Diffusion-weighted imaging; Imaging; Magnetic resonance imaging; Nasopharyngeal carcinoma; Positron emission tomography.

Fig. 1

Distinction between nasopharyngeal tumor (a & b) and adenoidal hyperplasia (c & d). Axial T2-weighted, fat-suppressed image shows intermediate signal slightly asymmetrical soft tissue occupying the bilateral nasopharynx with absence of the adenoidal septa (asterisk) (a). Axial T1-weighted post-contrast image with fat suppression shows moderate enhancement of the bilateral nasopharyngeal soft tissue mass with focal loss of the deep white mucosal line in the left lateral and posterior wall (arrows) (b). Biopsy confirmed nasopharyngeal carcinoma. Axial T2-weighted, fat suppressed image shows the symmetrical soft tissue in the bilateral nasopharynx containing cystic focus (asterisk) and preservation of hypointense adenoidal septa (arrowhead) (c). Axial T1-weighted post-contrast image with fat suppression shows symmetrical hypo-enhancing soft tissue with a striated appearance and preservation of deep mucosal white line (d). Findings are consistent with adenoidal hyperplasia

Fig. 2

Coexistence of nasopharyngeal tumor and lymphoid hyperplasia in a 70-year-old man referred for an enlarging right neck mass. Doppler ultrasound of the right neck shows a hypoechoic mass with increased peripheral vascular flow and a central anechoic cystic area with septations (a). Axial contrast CT of the neck shows an enlarged roundish right level II node with central hypoenhancing area suggestive of necrosis (b). Prominent soft tissue density in the nasopharynx was noted on the CT (not shown). Endoscopy found a right nasopharyngeal mass and biopsy was proven to be an undifferentiated carcinoma. Axial T2-weighted image shows soft tissue thickening of the bilateral nasopharynx. Small cysts are seen involving the bilateral nasopharynx, more on the left side. Minimal intermediate T2-weighted soft tissue thickening is seen at the lateral wall of right nasopharynx (asterisk) (c). The pharyngobasilar fascia is intact. Axial post-contrast T1-weighted, fat-suppressed image shows only non-specific moderately enhancing soft tissue thickening of the bilateral nasopharynx with intact deep mucosal white line (d). Coronal post-contrast, fat-suppressed T1-weighted image depicts a moderately enhancing mass in the right nasopharynx (asterisk) with focal loss of the deep mucosal white line at the roof (arrows) (e). Axial fusion FDG-PET/CT depicts the hyper-metabolic right nasopharyngeal mass and the hypermetabolic right level II node (not shown). Otherwise, no hypermetabolic distant metastasis (f). Radiological staging was T1N1M0 and the patient received radical radiotherapy. This case highlights three diagnostic pearls. First, the presence of benign lymphoid hyperplasia and tumor are not mutually exclusive. Second, the use of multiplanar reformat should be routinely performed for evaluation of the nasopharynx in order to avoid missing small tumors due to partial volume effect. Third, level II nodal metastasis can occur without involvement of the retropharyngeal node, especially for laterally located tumors in the nasopharynx

Fig. 3

Perineural tumor spread in a 60-year-old man presented with left maxillary facial numbness with biopsy-proven undifferentiated carcinoma in left nasopharynx. Axial post-contrast T1-weighted image with fat suppression shows the left nasopharyngeal tumor at the fossa of Rosenmüller (asterisk) (a). Axial post-contrast T1-weighted image with fat suppression at a higher level reveals asymmetric enlargement and enhancement of the left vidian canal extending anterolaterally into the left pterygopalatine fossa (arrows) (b). Axial post-contrast T1-weighted MR image with fat suppression at a further higher level shows asymmetric enlargement and enhancement of the left foramen rotundum along the cavernous sinus (arrows) (c). Coronal T1-weighted image without fat suppression shows the asymmetric enlargement of the left foramen rotundum (black arrowhead) and vidian canal with fat effacement (white arrowhead). The nasopharyngeal tumor extends to the left vidian canal with perineural spread (asterisk) (d). The apparent small tumor in the nasopharynx with underdetection of perineural tumor spread may lead to understaging and subsequent undertreatment with missing irradiation target and over-estimation of survival

Fig. 4

Grading of radiological extranodal extension from the Head and Neck Cancer International Group consensus recommendations [35]. Axial post-contrast T1-weighted image with fat suppression shows the left level II nodes demonstrating ill-defined nodal margin that extends into the perinodal fat (arrowhead). This is classified as grade 1 (a). Axial post-contrast T1-weighted image with fat suppression shows conglomerate left level II nodal mass (asterisk) with ill-defined nodal margin extending to the perinodal fat (arrowheads). This is classified as grade 2 (b). Axial post-contrast T1-weighted image with fat suppression shows conglomerate right level II nodal mass with extension to adjacent neck muscles (black arrows) (c). Axial post-contrast T1-weighted image with fat suppression shows conglomerate left level II nodal mass with extension to adjacent subcutaneous layer and skin (white arrows) (d). These are classified as grade 3

Fig. 5

Illustrative comparative images of a 76-year-old female with skull base osteomyelitis (a) and a 53-year-old man with locally advanced NPC (clinical stage T4N3M0) (b). Axial post-contrast T1-weighted, fat-suppressed image shows intensely enhancing, infiltrative soft tissue signal involving the bilateral nasopharynx without significant mass effect. Note the preserved deep mucosal white line (arrowheads) and the preserved architecture of the nasopharynx. There is extension into the bilateral hypoglossal canals (black asterisks) and intracranial extension into the left posterior fossa. Lateral extension of the enhancing soft tissue signal to involve the left parotid gland is observed (white asterisk). Extensive enhancing marrow signal is noted in the bilateral basioccipital, left petrous and tympano-mastoid temporal bone. No retropharyngeal or cervical lymphadenopathy (a). Axial T2-weighted, fat-suppressed image shows the characteristic intermediate signal for NPC (asterisk). There is associated mass effect especially on the left nasopharynx and left prevertebral muscle. Disruption of the normal architecture of nasopharynx is evidenced by the partial disruption of the pharyngobasilar fascia (dotted line). Limited left lateral extension of the tumor is observed as the tumor is still bound by the tensor veli palatini muscle (arrows) (b). Extensive bilateral cervical lymphadenopathies (not shown)

Fig. 6

Sphenoid sinus squamous cell carcinoma in a 63-year-old man presented with headache and right 6th nerve palsy (a & b). Initial plain CT brain showed a hyperdense right sphenoid mass with clival destruction (not shown). Axial post-contrast T1-weighted image with fat-suppression shows an irregular and infiltrative mass centered at right sphenoid sinus with clival, bilateral petrous apex destruction, and intracranial extension (not shown). The lesion shows irregular peripheral enhancement with central areas of hypo-enhancement (asterisk) (a). Axial T2-weighted image with fat-suppression shows the corresponding mass with heterogenous, predominantly hypointense signal (asterisk) (b). Invasive pituitary macroadenoma in a 73-year-old woman presented with persistent headache (c & d). Axial T2-weighted image with fat-suppression shows an extensive tumor mass with intermediate signal containing multiple internal cystic foci involving the central skull base (arrowhead) (c). Coronal post-contrast T1-weighted image with fat-suppression shows the lesion centered at the sella turcica and clivus with bilateral cavernous sinus extension. The nasopharyngeal roof is unremarkable (asterisk) (d)

Fig. 7

Delayed tumor regression and time lag between anatomical and metabolic regression in a 69-year-old man with locally extensive NPC (clinical stage T4N3M0) completed chemo-irradiation in 2023. Axial T1 post-contrast images with fat-suppression at pre-treatment stage show a large and infiltrative enhancing left nasopharyngeal tumor (arrow) and left level II lymphadenopathy (arrowhead) (a) & (b). There was evidence of pathological complete remission in the nasopharyngeal tumor at 10 weeks after completion of treatment. Axial T1 post-contrast images with fat suppression at 12 weeks show interval shrinkage in size of the known tumor with residual enhancing soft tissue in the left retropharyngeal and prevertebral space (arrow). The left level II node also shows interval shrinkage with residual heterogeneously enhancing soft tissue (arrowhead) (c) and (d). These were equivocal for residual tumors, which might warrant further palliative treatment. Axial fusion FDG PET/CT images at 12 weeks show the left nasopharyngeal lesion (arrow) as well as the left level II lesion (arrowhead) to be non-FDG avid, suggestive of metabolic resolution, despite the small residual soft tissue density. Apparent muscle activity along the bilateral longus colli muscles (asterisks) is a known diagnostic pitfall mimicking disease recurrence (e) and (f). FDG PET/ CT can be a helpful tool in this occasion due to its high negative predictive value. The patient subsequently underwent clinical observation instead of unnecessary biopsy or oncological therapy. Axial T1 post-contrast images at 24 weeks show almost complete resolution of the left nasopharyngeal lesion (asterisk) and the left level II node (arrowhead) (g) and (h)

Fig. 8

Typical signal characteristics of the recurrent nasopharyngeal tumor in a 72-year-old man with history of NPC (clinical stage T1N1M0) and radical radiotherapy completed in 2013. Axial T2-weighted image with fat-suppression shows an intermediate signal mass in the right nasopharynx causing focal expansion of the pharyngobasilar fascia which appears ill-defined (arrows). There is also extension of signal abnormality to the right prevertebral muscle (asterisk) (a). Axial T1-weighted image with fat-suppression shows the moderately enhancing mass in the right nasopharynx (arrow) with extension to right prevertebral muscle (arrow) (b). On the ADC map there is hypointense signal corresponding to the right nasopharyngeal mass (arrow) (c). Axial fusion FDG-PET/CT confirms the presence of a hypermetabolic mass in the right nasopharynx (d). Biopsy confirmed recurrent NPC

Fig. 9

Scar tissue in a 65-year-old man who had NPC (clinical stage T3N1M0) involving the right pterygopalatine fossa completed combined chemoirradiation in 2022. Post-treatment endoscopy revealed persistent tumor and therefore stereotactic radiotherapy was given. Axial T1-weighted post-contrast image with fat suppression shows the enhancing soft tissue at the right pterygopalatine fossa with local expansion (asterisk) suggestive of tumor (a). Axial T1-weighted post-contrast image with fat suppression performed at 18 months upon treatment completion shows interval shrinkage of the previous noted tumor at right pterygopalatine fossa but with persistent mildly enhancing soft tissue thickening (arrowhead) equivocal for residual tumor or scar (b). ADC map of the diffusion-weighted imaging performed at 18 months upon treatment completion showed no restricted diffusion in the right pterygopalatine fossa (arrowhead) (c). Axial fusion FDG-PET/CT at 18 months post-treatment depicts the right pterygopalatine fossa soft tissue to be non-FDG avid (d). The original tumor at the right nasopharynx has resolved (not shown). Findings are suggestive of scar tissue without viable tumor

Fig. 10

Post-radiation nasopharyngeal necrosis in a 49-year-old man with NPC (clinical stage T4N2M0). He developed epistaxis and progressive headache 6 months after radiotherapy. Nasoendoscopy showed crusted and ulcerated mucosa without mass. Axial contrast-enhanced CT image shows mucosal irregularity in bilateral nasopharynx. Rim-enhancing lesions are seen in bilateral nasopharynx with extension to carotid spaces encasing the internal carotid arteries (arrowheads) (a). Axial T2-weighted image with fat suppression shows the lesions to be heterogeneous in signal intensity (arrowheads) (b). Axial and coronal post-contrast T1-weighted image with fat suppression show focal defects in the bilateral nasopharynx as discontinuity of the deep mucosal line (arrows). The rim-enhancing lesions encasing the bilateral internal carotid arteries are again seen (arrowheads) (c) and (d). Deep biopsy was suspended due to the close relationship with internal carotid arteries. The lesions gradually resolved on conservative management with restoration of the continuity of the deep mucosal white line on follow-up MRI (not shown)

Fig. 11

Illustrative comparative images of a 49-year-old female with a hypertrophied superior cervical ganglion with history of treated NPC in 2014 (clinical stage T4N1M0) (a) to (c) and a 58-year-old man with recurrent retropharyngeal node 2 years post-treatment of locally advanced NPC (clinical stage T4N3M0) (d) to (f). Axial T1-weighted post-contrast image with fat suppression at 6 months post-treatment shows a sub-centimeter enhancing lesion with central hypointense dot at left retropharyngeal space (arrowhead) located anteromedial to the ipsilateral internal carotid artery (a). The lesion showed interval enlargement and then stabilized at 6 and 7 years upon treatment completion (not shown). Axial post-contrast T1-weighted image with fat suppression at 9 years post-treatment shows an enlarged lesion in the left retropharyngeal space (arrowhead). Its T2-weighted hyperintense signal persists. The internal architecture with central hypointense dot is maintained (b). Otherwise, the nasopharynx showed no mass all along to indicate recurrence (not shown). Axial FDG-PET fusion image shows the lesion being non FDG-avid (c). Overall findings are in keeping with a hypertrophied superior cervical ganglion after radiotherapy. Axial T2-weighted image with fat-suppression at 2 years post-treatment shows a new sub-centimeter left retropharyngeal node with intermediate signal intensity (arrowhead) (d). Axial T1-weighted post-contrast image with fat suppression at 2 years post-treatment shows the corresponding lesion to be avidly enhancing (arrowhead) (e). Axial FDG-PET fusion image shows the lesion being hypermetabolic (f). No other local recurrence or distant metastases was depicted. The patient underwent salvage open nasopharyngectomy and confirmed recurrent tumor in the retropharyngeal node

Fig. 12

Serial MRI demonstrating the signal change in the basisphenoid of a 56-year-old female with a history of localized NPC (clinical stage T1N0M0) in 2011 with pathological complete remission. Sagittal T1-weighted post-contrast MRI with fat suppression at baseline shows no evidence of signal abnormality at the clivus. The nasopharyngeal tumor is seen (asterisk) (a). There is progressive increase in the patchy enhancement in the clivus in 3-year and 9-year follow–up images (b) and (c), and the signal abnormality shows partial resolution in 12-year follow-up image (arrows) (d). Coronal T1 post-contrast MRI with fat suppression at baseline shows no evidence of signal abnormality at the basisphenoid (e). There is progressive increase in the patchy enhancement in the bilateral basisphenoid, more on left side, in 3-year follow-up image (f) and 9-year follow–up image (g), and the signal abnormality shows partial resolution in 12-year follow-up image (arrows) (h)

Fig. 13

Same patient as Fig. 6. Normal expected early post-operative appearance of open nasopharyngectomy in a 72-year-old man with recurrent NPC (clinical restaging T2N0M0). He had open right nasopharyngectomy via maxillary swing approach with vastus lateralis flap followed by post-operative stereotactic radiotherapy. A follow-up MRI was performed at 2-month after the operation. Axial T2-weighted image with fat-suppression shows the flap at the right nasopharynx appearing diffusely swollen with markedly hyperintense signal (asterisk) with perifocal soft tissue edema (arrowheads) (a). Axial T1-weighted post-contrast image with fat suppression shows the flap with heterogenous enhancement (asterisk) and perifocal soft tissue enhancement in the operative bed (arrowheads) (b). The imaging appearance of the flap was confused with residual tumor and additional FDG-PET/CT as well as follow-up MRI with DWI were performed. Axial fusion FDG-PET/CT shows the flap being diffusely eumetabolic (asterisk) (c). Conventional sequences on follow-up MRI after a further 2 months showed no interval change in size and signal characteristics of the flap (not shown). ADC map shows that there is diffuse hyperintense signal within the flap suggestive of facilitated diffusion (asterisk) (d). No residual or recurrent tumor was evident

Fig. 14

Normal expected post-operative appearance of open nasopharyngectomy in a 58-year-old man with NPC (clinical stage T4N3M0) completed chemo-irradiation in 2017. Two years after, he had a left retropharyngeal node recurrence on surveillance MRI (not shown) and subsequently an open nasopharyngectomy via maxillary swing approach and a flap reconstruction using temporalis muscle. Axial T1-weighted pre-contrast image without fat suppression one-year after the operation shows no recurrence, demonstrating normal fat striation of the temporalis muscle flap without soft tissue replacement (arrows) (a). Axial T1-weighted post-contrast image with fat-suppression shows non-mass like enhancement in the medial aspect of the flap (asterisk). The recipient bed of the flap shows a straight margin without discrete nodular enhancement (arrowheads) (b). Axial T2-weighted image with fat suppression shows mild non mass-like hyperintense signal (asterisk) (c). Coronal T1-weighted image without fat-suppression shows the smooth transition in the surgical bed and straight superior margin of the flap with respect to the sphenoid bone (arrowheads) (d)

Fig. 15

Same patient as Fig. 14. Recurrent tumor after open nasopharyngectomy in a 58-year-old man with NPC (clinical stage T4N3M0) completed chemo-irradiation in 2017 with retropharyngeal lymph node recurrence in 2019. He underwent open nasopharyngectomy via maxillary swing approach and a flap reconstruction using temporalis muscle in 2020. Axial T2-weighted image with fat suppression shows intermediate signal nodular lesion with irregular border at the recipient bed (arrowhead) (a). Axial T1-weighted image without fat-suppression shows the replacement of the loss of normal fatty streak of the flap with nodular soft tissue signal (arrowhead) (b). Axial post-contrast T1-weighted image with fat suppression shows the corresponding lesion to be intensely and homogenously enhancing (arrowhead). Encasement of ipsilateral internal carotid artery is noted indicating unresectable disease (asterisk) (c). Axial fusion FDG PET/CT image confirms hypermetabolism of the corresponding lesion (d). Overall findings are in keeping with recurrent tumor. He then received palliative chemotherapy for treatment

Fig. 16

Expected post-operative changes in a 51-year-old man who had NPC (clinical T3N2M0) and completed chemoradiation in 2022. He had recurrent NPC (rT1N0M0) one-year after completion of treatment and underwent transnasal endoscopic nasopharyngectomy. A surveillance MRI was performed at 6-month post-surgery. Axial T1-weighted image with fat suppression shows the posterior septectomy of the nasal septum (dashed line) and the absence of right inferior turbinate in keeping with inferior turbinectomy (white asterisk). The clivus shows diffusely increased T2-weighted signal suggestive of marrow edema (black asterisk) (a). Axial T2-weighted image with fat suppression shows the nasoseptal flap covering the bony defect of the bilateral posterior wall and right lateral wall of the nasopharynx with a deeper hypointense layer and a more superficial smooth thin T2-weighted hyperintense layer (arrows). The right torus tubarius has been resected. There is also enhancing marrow edema in the clivus related to bone drilling, in keeping with post-operative change (asterisk) (b)

Fig. 17

Same patient as Fig. 16. Recurrent tumor after endoscopic nasopharyngectomy in a 51-year-old man who had NPC (clinical T3N2M0) and completed chemoradiation in 2022. He had recurrent NPC (rT1N0M0) one-year after completion of treatment and underwent transnasal endoscopic nasopharyngectomy. A surveillance MRI was performed at 18-month post-surgery. Axial T2-weighted image with fat suppression at the superior resection margin shows infiltrative intermediate signal involving bilateral posterior and lateral walls of the nasopharynx (arrowheads). There is also perifocal patchy hyperintense signal involving the bilateral pterygoid bases and the clivus (a). ADC map shows the infiltrative soft tissue along bilateral nasopharyngeal walls to be hypointense (arrowheads) with hyperintensity on the high b-value DWI (not shown), in keeping with restricted diffusion (b). Axial post-contrast T1-weighted image with fat suppression shows the moderate enhancement of the soft tissue along bilateral nasopharyngeal walls (arrowheads), surrounded by marked enhancement in the adjacent soft tissue and the bone (c). Findings are suggestive of recurrent tumor along the nasopharyngeal walls on the background of post-operative change. Axial fusion FDG-PET/CT confirms the presence of hypermetabolic tumor along the nasopharyngeal walls. Otherwise no nodal or distant metastasis (d). Biopsy confirmed recurrent undifferentiated carcinoma