Branchial cleft cyst - Radiology

Ultrasound

• Well-defined, thin-walled cystic lesion.
• Usually anechoic or homogeneously hypoechoic.
• May contain fine internal debris, giving pseudo-solid appearance.
• Posterior acoustic enhancement is common.
• No internal vascularity on Doppler.
• Infection causes internal echoes, septations, wall thickening, and peripheral hyperemia.

CT neck with contrast

• Well-circumscribed, round/ovoid, non-enhancing, low-attenuation lesion.
• Usually lies anterior to SCM and lateral to carotid space, commonly at the mandibular angle.
• In a second cleft cyst, extension or a tapered “beak/notch” between the internal and external carotid arteries is highly suggestive.
• Infected cyst: thick irregular rim enhancement, surrounding fat stranding, possibly fluid-fluid level or abscess formation.

MRI

• T1: usually low signal, but may be high with proteinaceous fluid, hemorrhage, or infection.
• T2/STIR: high signal intensity.
• No internal enhancement in an uncomplicated cyst. Thin rim enhancement may occur.
• MRI is useful for defining a sinus/fistulous tract and relation to carotid vessels, parotid gland, and facial nerve.

Typical locations by type

Differential diagnosis

• Cystic metastatic cervical lymph node, especially HPV-associated oropharyngeal squamous cell carcinoma in adults
• Necrotic lymphadenopathy, including tuberculous nodes
• Lymphatic malformation
• Thyroglossal duct cyst, usually midline
• Dermoid/epidermoid cyst
• Abscess, plunging ranula

Important exam point

Classification of orbital tumours

• Children: retinoblastoma, rhabdomyosarcoma, optic nerve glioma, dermoid, capillary haemangioma, leukemic infiltrate.
• Adults: cavernous venous malformation, lymphoma, meningioma, lacrimal gland tumours, metastasis, and uveal melanoma.

Radiological features of tumours affecting the globe

1. Retinoblastoma

Ultrasound

• Intraocular echogenic retinal mass.
• Calcification causes acoustic shadowing, a highly useful finding.
• Internal vascularity on colour Doppler.
• May show retinal detachment, vitreous seeding, hemorrhage, or pseudohypopyon.

CT

• Hyperattenuating soft-tissue mass, usually in the posterior globe.
• Nodular or stippled calcification is characteristic and is seen in most cases.
• Contrast enhancement is present.
• Assesses bony orbit and gross extraocular extension, but CT is now avoided where feasible in children because of ionizing radiation and the risk of radiation-induced second malignancy in hereditary disease.

MRI

• Best modality for local staging and intracranial assessment.
• Tumour is typically:
  • T1: intermediate to hyperintense relative to vitreous.
  • T2: relatively hypointense compared with vitreous.
  • Post-contrast: moderate to marked enhancement.
  • DWI: restricted diffusion.
• Look specifically for:
  • Optic nerve invasion, especially post-laminar involvement.
  • Scleral/extrascleral extension.
  • Choroidal invasion.
  • Orbital extension.
  • Pineal or suprasellar primitive neuroectodermal tumour in hereditary disease, termed trilateral retinoblastoma.

2. Uveal melanoma

Ultrasound

• Solid, dome-shaped or mushroom-shaped choroidal mass.
• Low-to-medium internal echoes on A-scan.
• Homogeneous echogenic lesion on B-scan.
• Associated exudative retinal detachment is common.
• Colour Doppler shows internal vascularity.

CT

• Hyperdense enhancing intraocular mass.
• Usually non-calcified.
• May demonstrate globe deformation, retinal detachment, scleral thickening, or extrascleral extension.
• CT is less specific than MRI for melanoma characterization.

MRI

• T1: hyperintense relative to vitreous.
• T2: hypointense relative to vitreous.
• Moderate to marked homogeneous enhancement after gadolinium.
• May be dome-shaped, lentiform, or have a mushroom configuration when the tumour breaks through Bruch membrane.
• MRI is valuable for detecting extrascleral spread, optic nerve involvement, and associated retinal detachment.

3. Choroidal metastases

• Most common intraocular malignancy overall in adults.
• Usually from breast carcinoma in women and lung carcinoma in men.
• Often bilateral and multifocal.
• Preferentially involve the posterior choroid.

Imaging

• Ultrasound: plateau-shaped, relatively echogenic choroidal mass with subretinal fluid.
• CT/MRI: enhancing choroidal or subretinal thickening/mass.
• MRI signal is variable and lacks the characteristic melanotic MRI pattern.
• Associated retinal detachment is frequent.
• Search for systemic primary malignancy and other metastatic deposits.

4. Medulloepithelioma

Imaging

• Arises from the ciliary body, therefore located anteriorly in the globe.
• Multiloculated cystic and solid intraocular mass.
• Ultrasound: echogenic solid portions with cystic spaces.
• CT: enhancing ciliary-body mass; dystrophic calcification may occur.
• MRI: heterogeneous lesion, commonly T2 hyperintense cystic areas with enhancing solid components.
• Can mimic retinoblastoma, but ciliary-body origin and multiple cystic spaces favour medulloepithelioma.

5. Choroidal haemangioma

Circumscribed choroidal haemangioma

• Solitary, benign vascular tumour.
• Usually a well-defined orange-red posterior choroidal lesion.

Imaging

• Ultrasound: acoustically solid echogenic choroidal mass.
• MRI: typically hyperintense on T2 and enhances strongly.
• Associated exudative retinal detachment may occur.
• Unlike melanoma, it is generally T2 hyperintense, whereas melanotic melanoma is usually T2 hypointense.

Diffuse choroidal haemangioma

• Associated with Sturge-Weber syndrome.
• Diffuse thickening of the choroid and may produce glaucoma or retinal detachment.

6. Intraocular lymphoma/leukemic infiltration

• May involve the retina, choroid, vitreous, optic nerve, or uvea.
• MRI may show diffuse or focal enhancing intraocular/uveal thickening with restricted diffusion.
• Often associated with CNS lymphoma or systemic hematologic malignancy.
• Leukemic infiltration may be diffuse; retinal hemorrhages are common in leukemia.

Imaging differentiation: retinoblastoma vs melanoma

General radiological approach to an intraocular mass

1. Ultrasound with Doppler: first-line for lesion location, calcification, internal vascularity, and retinal detachment.
2. MRI orbit with contrast and DWI: best for lesion characterization, optic nerve/scleral/extraocular spread, and intracranial extension.
3. CT: best for calcification and bone, but use selectively, especially in children.
4. Assess for complications: retinal detachment, vitreous seeding, hemorrhage, glaucoma, optic nerve invasion, extrascleral extension, and distant metastasis.