Implementing and interpretating the CT dacryocystography require a comprehension of the anatomy of the lacrimal drainage system. Within the corner of the internal eye, there is a lacrimal lake where tears gather. After that, the tears pass via the lacrimal punctums and through the upper and lower canalicles, then the union canal, the sac, and finally the nasolacrimal tear duct, which terminates at the tear duct located in the lower meatus of the nasal fossae.
CT dacryocystography is requested in two main situations, lacrimal drainage system blocks and medial canthal mass. Infections, acute sinusitis, acute dacryocystitis, acute canaliculitis, and the standard contraindications for contrast agents are its primary contraindications.
Normal radiological findings of a CT dacryocystography:
According to cross-sectional imaging, the anterior lacrimal crest of the maxillary bone and the posterior lacrimal crest of the lacrimal bone form the bony lacrimal fossa, which is home to the lacrimal sac. It can be filled with fluid (tear) or air filled in normal state. The anterior and posterior slips of the orbicularis oculi muscle invest the lacrimal sac as it adheres to the lacrimal crests, making it a preseptal structure. The nasolacrimal duct slopes posteriorly and ends below the inferior turbinate. It consists of both intraosseous and membranous sections.
Contrast opacification helps visualize the two lacrimal canaliculi with a symmetrical diameter, and the union canal (Figure 2, 3 and 4), and shows no resistance while cannulisation. The content of the lacrimonasal duct after opacification can be heterogenous but always permeable, with the passage of the contrast medium in the nasal fossae.
Pathological radiological findings of a CT dacryocystography:
- Stenosis in the lachrymal apparatus:
The radiological appearance depends on the location of the stenosis. The CT dacryocystography in case of a blockage, allows to detect it, characterise it, and analyse the level of blockage.
The stenosis can be congenital due to the persistence of the membrane at the valve of Hasner, or acquired, secondary to trauma, surgery, inflammatory diseases, and primary acquired nasolacrimal duct obstruction.
Dacryolithiasis is seen in patient with a narrow nasolacrimal dust causing stagnation of the tears. Their composition is diverse, and therefore, their appearance depends on it; isodense if rich in phorphore proteins and hyperdense if rich in calcium.
On CT dacryocystography, lithiasis appears as a subtractive, lacunar image, molded by conctrast medium. The obstruction is usually partial, with the contrast medium passing downstream and into the nasal cavity.
- Pathology of the lachrymal sac:
Dacryocystocele is characterized by the accumulation of contrast agent within the lacrimal sac, resulting in a notable absence of its passage into the nasolacrimal duct
Acute dacryocystitis can cause a blockage in the drainage lacrimal apparatus, however it’s a contraindication for CT dacryocystography.
In case we deal with a medial canthal mass, CT dacryocystography allows us to analyse its structure and its relationship with the lacrimal drainage system (Figure 6). The CT dacryocystography gives us an excellent analyse of the bone structure of the rhino sinus, important in case of a planned endoscopic surgery.
Pre- and post-operative role of CT dacryocystography
An imaging assessment of the rhinosinus cavity plays a crucial role in the preoperative planning of nasosinus surgery or endonasal dacryocystorhinostomy. This assessment should be integrated into the CT dacryocystography to avoid the need for additional examinations and minimize radiation exposure. Surgical procedures, such as anterior ethmoidectomy, partial anterior unciformectomy, removal of ethmoidal cells, or partial middle turbinectomy, may be involved. The intricate relationships between the lacrimal gutter and the anterior ethmoid, the unciform process, and the middle turbinate operculum require careful exploration. Additionally, the presence of meningeal procidence must be addressed, and efforts made to rule out the existence of a concha bullosa, as it may pose challenges during the surgical procedure.
Three anatomical factors are usually found in cases of failed dacryocystorhinostomy: synechia between the bony stoma and the nasal septum, and fibrosis of the osteotomy orifice, both visible by nasal endoscopy, and the sump syndrome diagnosed on CT scan, which shows a residual lacrimal sac that doesn't open properly or opens too high into the nasal cavity.
