Anatomy of the Nasopharynx

The nasopharynx is a tubular structure that extends from the skull base, specifically the clivus and the floor of the sphenoid sinus, down to the level of the soft palate. The anterior border is formed by the choanae and the bony vomer, while the posterior border includes the clivus, the upper two cervical vertebrae, and the superior constrictor muscle, which is closely bound to the prevertebral fascia. A comprehensive anatomical depiction is presented in Figures 2 and 3.

Fig 2: Anatomy of the Nasopharynx 1

Fig 3: Anatomy of the Nasopharynx 2

1. The Good (Benign Lesions)

Tornwald Cyst

• Remnant of notochord
• Midline, submucosal, round cysts between prevertebral muscles
• Usually asymptomatic
• Incidentally seen in 5% of routine brain MRI.
• T1 & T2 signal may change depending on protein concentration (hyperattenuating on CT).
• May have minimal enhancement of the cyst wall.
• Large/infected cysts may cause halitosis, postnasal discharge, occipital headache, and unpleasant taste in the mouth.

Fig 4: Axial T1-weighted (a), T2-weighted (b), and post-contrast T1-weighted images (c) reveal the presence of a midline nasopharyngeal cystic lesion. This lesion is characterized by a high signal on the T1 images, which is indicative of its protein-rich content, in addition to a slight rim enhancement observed in the post-contrast images.

Fig 5: Axial (a) and sagittal (b) T1-weighted, fat-saturated T2-weighted (c), and contrast-enhanced CT images (d) demonstrate the presence of a giant Tornwaldt cyst in a patient exhibiting halitosis and nasopharyngeal discharge.

Retention Cyst

• Obstructed submucosal mucinous glands
• Incidental lesion, usually asymptomatic
• Lateral or paramidline, ovoid, unilocular, usually homogeneously T2 hyperintense lesions (T1 & T2 signal may vary due to protein content)
• No significant enhancement in wall.
• May be multiple or septated and associated with lymphoid hyperplasia.
• Large cysts may obstruct the eustachian tube and cause mastoid & middle ear effusion.

Fig 6: Axial fat-saturated T2-weighted (a), coronal T2-weighted (b), and axial post-contrast T1-weighted images (c) indicate the presence of multiple septated small retention cysts in the nasopharynx, accompanied by benign lymphoid hyperplasia.

Fig 7: Axial fat-saturated T2-weighted (a), coronal T2-weighted (b), and axial post-contrast T1-weighted images (c) display bilateral pear-shaped nasopharyngeal retention cysts located in the right and left Rosenmüller fossae. Note the high T1 and low T2 signal on the right, suggesting proteinaceous content. The ADC map (d) indicates high signal. Also, note the mastoid effusion on the left (asterisks).

Lymphoid Hyperplasia

• Common in children and young adults but seen at any age.
• Frequently associated with HIV infection.
• Symmetric enlargement, though asymmetry can occur.
• No invasion of adjacent tissues or lymphadenopathy
• Striped Appearance: Contrast-enhancing linear septa (dark = lymphoid tissue, bright = mucosa/submucosa)
• Important to differentiate from early-stage nasopharyngeal cancer!

Fig 8: Axial fat-saturated T2-weighted image (a) demonstrates a significant thickening of the nasopharynx. Post-contrast T1-weighted image (b) reveals a striped appearance within the nasopharynx. The endoscopic image (c) indicates the presence of adenoid hypertrophy. The pathological specimen (d) displays lymphoid tissue, with no evidence of malignancy identified.

Fig 9: Axial post-contrast T1-weighted image (a) reveals thickening of the nasopharynx exhibiting a striped appearance, which is consistent with lymphoid hyperplasia. Axial fat-saturated T2-weighted image (b) and ADC map (c) demonstrate the presence of multiple enlarged cervical lymph nodes. Note the low bone marrow signal on the sagittal T1-weighted image (d).

Fig 10: Various manifestations of adenoidal benign lymphoid hyperplasia

Vascular Malformation

• Vascular malformations may occur anywhere in the head and neck.
• Soft and compressible, bluish mucosal color
• Very bright T2 signal, gradual contrast enhancement (fills in on delayed phases)
• High ADC values
• Phleboliths are the key (but may mimic flow void on MRI!)

Fig 11: Axial T1-weighted imaging (a) reveals a hypointense lesion within the left half of the nasopharynx. Marked hyperintensity is observed on axial fat-saturated T2-weighted imaging (b), along with gradual enhancement on post-contrast axial (c) and sagittal (d) images. ADC map (e) shows a high signal. Findings are compatible with a venous malformation. Note the phlebolith (red arrowhead).

Eustachian Fibrolipoma

• Benign, slow-growing rare tumor composed of both fibrous and fatty tissues.
• May cause obstruction, impairing normal ventilation of the middle ear and leading to functional symptoms.
• Hyperintense fat signal is observed in T1 and T2-weighted imaging.
• The fibrous component shows intermediate to hypointense T1 and T2 signals.
• Minimal enhancement in fibrous areas; fatty areas remain non-enhancing.

Fig 12: Axial T1-weighted image (a) demonstrates a hypointense mass lesion with a small fat signal in the left eustachian tube. Coronal T2-weighted (b) and axial fat-saturated T2-weighted (c) images reveal a hypointense lesion with a dominant fibrous component. Axial post-contrast T1-weighted image (d) indicates minimal contrast enhancement in the lesion. Note that the fat component follows the fat signal in all series (red arrowhead).

2. The Bad (Malignant Lesions)

Nasopharyngeal Carcinoma (NPCa)

Let’s start with a quiz case!

Fig 13: Quiz Case

• The most common primary malignancy of the nasopharynx.
• Mucosal tumor of lateral pharyngeal recess (fossa of Rosenmüller)
• 25%: Keratinizing NPCa : Smoking, alcohol, elder patients
• 75%: Nonkeratinizing NPCa: Endemic, strongly associated with EBV, 15% differentiated, 60% undifferentiated type
• Clinical Presentation: Neck mass from lymph node metastasis (70%), epistaxis, serous otitis, conductive hearing loss, otalgia

*A comprehensive staging of NPCa is illustrated in Figure 14-18.

Fig 14: T Staging of Nasopharyngeal Carcinoma 1

Fig 15: T Staging of Nasopharyngeal Carcinoma 2

Fig 16: T Staging of Nasopharyngeal Carcinoma 3

Fig 17: N Staging of Nasopharyngeal Carcinoma

Fig 18: Axial fat-saturated T2-weighted image (a) and axial post-contrast T1-weighted image (b) reveal a bulky mass lesion filling the nasopharynx, invading the lateral and medial pterygoid muscles, as well as the prevertebral muscles on the left. Coronal post-contrast T1-weighted image (c) illustrates enlargement and increased contrast enhancement of the vidian canal and foramen rotundum on the left, suggesting perineural invasion (T4) (red arrows). Coronal post-contrast T1-weighted image (d) displays metastatic lymph nodes extending below the cricoid (N3). Note the increased enhancement of the left pterygoid muscles associated with denervation atrophy (orange arrow).

Quiz Case Answer

Fig 19: Quiz Case Answer

Lymphoma

• The second most common malignancy of the nasopharynx in adults.
• A homogeneous mass in the nasopharynx with minimal deep structure invasion may suggest lymphoma.
• Cervical lymphadenopathy is present in nearly half of the patients.
• Lymphoma has a tendency to extend down into the oropharynx rather than up into the skull base.
• They usually have slight contrast enhancement, low ADC values, and high FDG uptake.

Fig 20: Axial T1-weighted (a), axial fat-saturated T2-weighted (b), and post-contrast T1-weighted (c) images reveal a bulky mass lesion occupying the nasopharynx without invading surrounding tissues. Note the bilateral mastoid effusion (asterisks).

Rhabdomyosarcoma

• Most common solid tumor in children.
• Involvement of the head and neck is observed in approximately 35% to 40% of cases cases.
• Parameningeal location involves nasopharynx, nasal cavities, paranasal sinuses, infratemporal, pterygopalatine fossae, and middle ear cavity.
• Nasopharyngeal rhabdomyosarcoma may mimic benign conditions like nasal obstruction, snoring, or sinus issues.
• MRI is best for soft tissue and intracranial involvement; T1 is isointense, and T2 shows variable signals and restricted diffusion.

Fig 21: Axial T1-weighted image (a) reveals an isointense mass lesion located in the nasopharynx. The axial fat-saturated T2-weighted image (b) displays a heterogeneous hyperintense mass. Post-contrast axial (c) and sagittal (d) images indicate heterogeneous contrast enhancement within the lesion.

Chondrosarcoma

• 5% of all skull base tumors
• Typically forms expansile mass with multilobulated margins.
• Paramedian origin (petro-clival synchondrosis) favors chondrosarcoma rather than midline location for chordoma.
• Hyperintense signal due to the gelatinous matrix of the tumor.
• 50% of the tumors show ring and arc calcification.

3. The Radiologically Weird (Rare or Atypical Lesions)

Juvenile Nasopharyngeal Angiofibroma

• Benign, locally aggressive tumor in adolescent males.
• Common symptoms: nasal obstruction and epistaxis.
• Originates from the sphenopalatine foramen extends into the nasopharynx and pterygopalatine fossa.
• Rarely causes bone destruction.
• Heterogeneous T2 signal and flow voids appear dark.
• Shows intense contrast enhancement.
• ADC values are usually higher than malignant lesions. 

Fig 22: Axial contrast-enhanced CT (a) and the axial fat-saturated T2-weighted image (b) reveal a heterogeneous mass lesion occupying the right nasal cavity, the sphenopalatine foramen, and the pterygopalatine fossa, extending into the nasopharynx. Axial (c) and sagittal (d) post-contrast T1-weighted images display significant contrast enhancement in the lesion. On the axial T2-weighted image (b), note the flow void caused by the dense vasculature within the lesion (green arrowhead).

Chordoma

• Rare malignant midline mass with local invasion.
• Originates from notochord remnant cells.
• Arises from spheno-occipital synchondrosis.
• Lytic osseous destruction of adjacent bone
• Irregular intratumoral calcification (sequestra from bone destruction)
• T2 marked hyperintense due to mucin “Lightbulb bright”
• Sometimes “honeycomb” appearance can be seen.
• Variable enhancement
• Lower ADC values than chondrosarcoma

Fig 23: Sagittal non-contrast CT image (a) reveals an expansile soft tissue mass lesion with intratumoral calcification that extends toward the nasopharynx, resulting in destruction of the clivus. The axial T1-weighted image (b) displays a central hypointense mass lesion at the level of the clivus. The axial fat-saturated T2-weighted image (c) demonstrates a significantly hyperintense mass lesion, while the sagittal post-contrast T1-weighted image (d) illustrates a heterogeneously enhancing mass lesion characterized by a honeycomb-like appearance.

Skull Base Menengioma

• Benign, slow-growing tumor arising from the meningothelial cells.
• An infiltrative, mass-forming lesion is present in the skull base, with potential extension into extracranial regions.
• Symptoms depend on location and include cranial nerve palsies, headaches, visual disturbances, and hearing loss.
• T2 signals can vary from hypo- to hyperintense.
• Low ADC values
• Intense homogeneous enhancement, “dural tail sign”
• Hyperostosis of the affected bone is the key imaging feature!

Fig 24: Axial T1-weighted image (a) demonstrates a diffusely infiltrating mass lesion affecting the skull base, extending into the nasopharynx, masticator area, prevertebral area, and clivus. Axial post-contrast T1-weighted image (b) reveals intense enhancement of the lesion. ADC map (c) indicates diffusion restriction. Non-contrast CT image (d) displays diffuse hyperostosis in the affected bone structures.

Follicular Dendritic Cell Sarcoma

• Rare neoplasm that originates from follicular dendritic cells in lymphoid follicles.
• Usually involves the lymph nodes, especially the head and neck area.
• Rarely, extranodal sites may be affected, including nasopharynx, tonsils, and oral cavity.
• Associated with Epstein-Barr Virus (EBV) and Castleman disease.
• No specific imaging findings, diagnosis is highly challenging regarding its rarity.
• Heterogeneous nasopharyngeal mass with areas of necrosis
• Intense enhancement

Fig 25: Axial T1-weighted image (a) reveals a hypointense mass lesion occupying the right and central portion of the nasopharynx. The axial T2-weighted image (b) illustrates a heterogeneous lesion featuring necrotic areas. The ADC map (c) displays a notable low signal. The post-contrast T1-weighted image (d) demonstrates heterogeneous and intense contrast enhancement within the lesion. A preliminary diagnosis of nasopharyngeal cancer was made based on imaging findings, and the pathology report indicated follicular dendritic cell sarcoma.

Nasopharyngeal Paraganglioma

• Paragangliomas of the sinonasal tract and nasopharynx are extremely rare.
• Might be sporadic or associated with Pheochromocytoma-Paraganglioma Syndromes.
• Well-circumscribed and strongly enhancing mass
• Salt & Papper appearance on MRI
• Biopsy is necessary to differentiate it from other benign and malignant nasopharynx tumors.

Fig 26: Axial T1-weighted image (a) reveals a mass extending from the right half of the nasopharynx into the nasal cavity. The axial T2-weighted image (b) shows the lesion as slightly hyperintense with small flow voids observed. The axial post-contrast T1-weighted image (c) and CT with arterial phase (d) demonstrate avid enhancement of the lesion.

Nasopharyngeal Castleman Disease

• Rare lymphoproliferative disorder that can affect single or multiple lymph nodes.
• Extremely rare in nasopharynx
• Homogeneous mass with increased enhancement
• Associated homogeneous lymph nodes
• Hypointense signals in the lesion likely indicate flow voids of feeding vessels, suggesting hyaline vascular variant

Fig 27: Axial fat-saturated T2-weighted image (a) reveals a small mass in the right half of the nasopharynx. Axial post-contrast T1-weighted images (b,c) demonstrate homogeneous enhancement of the mass in the nasopharynx and a uniform pathologic lymph node with increased enhancement at the left level 2B. PET images (d,e) indicate increased FDG uptake. The biopsy result is Castleman disease.

Nasopharyngeal Toxoplasmosis

• Rare manifestation of Toxoplasma gondii infection, primarily affecting immunocompromised individuals.
• Reactivation of latent Toxoplasma gondii cysts due to weakened immune system
• Inflammation and granuloma formation in nasopharynx
• Diffuse nasopharyngeal and oropharyngeal thickening with systemic symptoms
• Irregular enhancement
• Requires serological tests, PCR, and histopathology to confirm the diagnosis.

Fig 28: Sagittal T1-weighted (a), sagittal T2-weighted (b), and axial fat-saturated T2-weighted (c) images reveal a uniform mass extending from the nasopharynx to the oropharynx. The sagittal post-contrast T1-weighted (d) image demonstrates mild heterogeneous contrast enhancement in the mass. Histopathology revealed tachyzoites and cysts within the inflamed tissue, along with granulomatous inflammation.

Necrotising External Otitis Masquerading as Nasopharyngeal Carcinoma

• Severe, necrotizing infection of the external auditory canal that can extend to the skull base.
• May mimic nasopharyngeal carcinoma due to overlapping radiologic findings, such as bony destruction and soft tissue changes, with middle ear and mastoid opacification.
• Elderly patients with uncontrolled diabetes, complaining of severe otalgia, cranial nerve findings, and negative biopsy for malignancy, are highly suspicious for skull base osteomyelitis.
• The preservation of fascial planes and higher ADC values aids in diagnostic evaluation.
• Usually, there is no associated lymph node.

Fig 29: Axial (a) and coronal (b) T1-weighted images reveal a lesion protruding into the left nasopharynx, affecting the masticator area and the left temporomandibular joint and causing destruction of the clivus. Axial post-contrast T1-weighted image (c) reveals intact fascial planes; however, increased soft tissue enhancement is present in the region. Note the effusion in the mastoid cells on coronal T2-weighted image (d). The biopsy revealed no evidence of malignancy; however, the culture indicated the presence of Pseudomonas aeruginosa.