Dacryocystography

Dacryocystography (DCG) is a radiographic study of the lacrimal drainage system (canaliculi, lacrimal sac and nasolacrimal duct) after contrast is injected through a cannula in the lower (and sometimes the upper) lacrimal punctum.

Water soluble contrast (0.5 to 2 mL, or oil based contrast, which gives a denser image) is injected slowly until it flows into the sac and duct, and images are taken at once and after a delay of 10 to 20 minutes, with the patient supine and the head fixed.

In digital subtraction dacryocystography, a subtraction image shows the lacrimal system without bone, and the effective dose is very low (under 0.1 mSv), though the eye lens is in the field. Dacryoscintigraphy shows function with a radiotracer, and CT dacryocystography adds the bony canal and surrounding structures. MR dacryocystography with saline or gadolinium shows the duct without radiation.

Epiphora (watering eye) affects up to 3% of adults presenting to ophthalmology and is caused by a blocked lacrimal drainage system in about half. Congenital nasolacrimal duct obstruction affects 5 to 6% of newborns and resolves spontaneously in over 90% by one year.

Syringing and probing of the tear duct, nasal endoscopy and imaging help decide between conservative treatment, dilatation or stenting, and dacryocystorhinostomy. DCG is used when the site, extent and cause of a blockage, and the anatomy of the sac, are needed before surgery.

Indications. Persistent epiphora where the site of obstruction needs defining. Recurrent dacryocystitis, mucocele or discharge from the sac. Failed probing or syringing in the child. Before and after dacryocystorhinostomy to assess the surgical anastomosis. Suspected lacrimal sac tumour, stones (dacryoliths) or diverticulum.

Trauma to the medial canthus or nasal region with suspected canalicular or duct injury. Congenital anomalies (fistula, atresia, mucocele in a newborn). Suspected canalicular obstruction from drugs, radiotherapy or infection. Not for simple epiphora from lid laxity, ectropion, or dry eye, for which clinical examination, syringing and lid assessment come first.

Contraindications and precautions. Acute dacryocystitis or an acute infection of the sac (treat first with antibiotics, and avoid cannulation). Allergy to iodinated contrast (a small amount reaches the nose or throat). Pregnancy: avoid unless essential. Recent lacrimal surgery or trauma with an open wound.

Oil based contrast is avoided in infection and is used cautiously in children because it may cause granuloma. The patient is warned of a bitter taste if contrast reaches the pharynx. Local anaesthetic drops are used. Eye protection, and restraint or sedation, may be needed in children.

Preparation and technique. A control film is taken first. The punctum is dilated with a punctum dilator, a fine cannula is introduced into the canaliculus (the lower is easier), and contrast is injected gently with the patient lying down. Spot films or a subtraction series are taken immediately and at 10 to 15 minutes (a delayed film).

Both sides can be studied together, and a simultaneous bilateral injection is used when comparing sides. Films are taken in the anteroposterior (posteroanterior) and lateral projections, with a nasal cavity film to show contrast reaching the nose.

Normal appearances. The upper and lower canaliculi are thin vertical and horizontal tubes (0.3 to 0.5 mm) that join in the common canaliculus and enter the lacrimal sac. The sac is a smooth, oval or elongated structure about 10 to 12 mm long, positioned in the lacrimal fossa.

The nasolacrimal duct runs downward and slightly backward about 12 to 18 mm within the bony canal, and opens under the inferior turbinate (the inferior meatus). Contrast flows freely to the nose within seconds and little remains in the sac on the delayed film (under 5 to 10 minutes). Contrast is seen in the nasal cavity or the nasopharynx.

Interpretation.

• Nasolacrimal duct obstruction: contrast fills the sac, which is often dilated, with a cutoff at the level of the duct, no flow into the nose, and retention of contrast in the sac on the delayed film. The site (upper, mid or lower duct) and shape of the obstruction (a tapered "beak" for stenosis, abrupt for complete blockage) are described.
• Dacryocystitis and mucocele: a dilated sac with retained contrast and irregular outline.
• Canalicular obstruction: contrast fails to reach the sac or passes through a stenosis or a stricture of the common canaliculus, with dilatation of the canaliculus proximal to it.
• Dacryoliths: filling defects in the sac or duct, round or irregular, often with dilatation of the sac.
• Diverticulum of the sac: a smooth outpouching of the sac wall.
• Tumours of the sac: an irregular filling defect or a distorted sac with an irregular wall, with a mass extending outside the sac, and the appearance should prompt CT or MR and biopsy (squamous cell carcinoma, lymphoma, papilloma).
• Fistula: contrast tracks to the skin or the nose through a fistula, often congenital (a fistula of the lacrimal sac at the medial canthus).
• Congenital anomalies: atresia of the duct, mucocele (dacryocystocele) in a newborn, and valve of Hasner persistent membrane.
• Post-surgical: after dacryocystorhinostomy, contrast should pass from the sac through the new ostium into the nose; absence of flow indicates ostium closure, granulation, or scarring.
• Trauma: fractures of the lacrimal fossa and canal, with displaced or lacerated duct, and extravasation of contrast.
• Extrinsic compression: from nasal or sinus masses (mucocele, polyps, tumours), bony deformity or fibrous dysplasia.

Critical values and findings needing immediate action.

• Acute dacryocystitis with orbital cellulitis (fever, proptosis, restricted eye movements, loss of vision): urgent intravenous antibiotics, CT of orbit and sinuses, and ophthalmology and ear nose and throat review.
• Features of tumour (mass with bone erosion, bloody discharge, a fixed hard mass in the sac region): urgent CT or MR, biopsy and oncology referral.
• Anaphylaxis to contrast: stop, adrenaline, oxygen and resuscitation.
• Congenital dacryocystocele with respiratory distress (intranasal cyst in a neonate): urgent paediatric ear nose and throat and ophthalmology review, as newborns breathe through the nose.
• Contrast extravasation with an abscess: antibiotics and surgical drainage.

Limitations and artefacts.

• The study is dynamic only in a limited way: it shows anatomy and not flow physiology, and a patent system on syringing may still cause epiphora from a functional block (failure of the lacrimal pump), for which scintigraphy is used.
• Reflux of contrast to the conjunctiva or skin, injection pressure that opens a closed system, and extravasation produce false results. A false obstruction results from spasm or poor technique.
• Cannulation can injure the punctum or canaliculus, producing a false passage.
• The study shows the lumen only and does not show the bony canal, the surrounding mass, or sinus disease; CT or MR is needed.
• Soft tissue and mucosal disease of the nose and the inferior meatus (a common cause of obstruction) require nasal endoscopy.
• Contrast reactions are uncommon, and infection after instrumentation occurs in a small number of cases.
• The dose to the lens is low, but the study should be justified because most patients are managed with clinical tests and endoscopy; ultrasound, CT dacryocystography and MR dacryocystography avoid injection pressure or ionising radiation to differing degrees.
• Oil based contrast can cause granuloma if extravasation occurs.

Special groups.

• Newborns and infants: probing is the treatment for persistent blockage after 6 to 12 months; imaging is reserved for failed treatment or complex anomalies (dacryocystocele, atresia).
• Adults: acquired obstruction is commonest in middle aged and older women, usually from age related stenosis of the nasolacrimal duct.
• Patients after chemotherapy or radiotherapy: canalicular stenosis from drugs (fluorouracil, docetaxel) or radioactive iodine.
• Patients with facial trauma: orbital and nasoethmoid fractures damage the duct.
• Pregnancy: avoid.
• Regions: trachoma, chronic dacryocystitis and delayed presentation of mucocele and tumours are seen, and DCG may be the only imaging available before surgery; congenital obstruction with delayed care is common.

Follow up tests. Lacrimal syringing and probing, fluorescein dye disappearance test, nasal endoscopy to inspect the inferior meatus and the duct opening, CT dacryocystography or MR dacryocystography, dacryoscintigraphy, CT or MR of the orbit, sinuses and nose for tumour, biopsy of the sac mass, microbiology of discharge, and referral to oculoplastic, ophthalmology or ear nose and throat services for dacryocystorhinostomy, stenting or intubation.