Imaging Modalities for Lacrimal Disorders

Fig. 10.1
Plain DCG in a trauma setting showing a right distal nasolacrimal duct obstruction (Photo courtesy: Gangadhar Sundar, Singapore)

Digital Subtraction Dacryocystography (DS-DCG)

DS-DCG was first described by Galloway et al. in 1984 [2]. DCG is a useful modality to study the anatomical abnormalities of the lacrimal system such as stenosis, obstructions, diverticula, and to detect dacryolithiasis [26]. Digital subtraction dacryocystography is currently the most favored among conventional X-ray techniques. As the name reflects, this technique can subtract background images and noises to give a clear contrast-filled lacrimal image for study (Figs. 10.2 and 10.3). Its other advantages include reduced radiation exposure as compared to conventional techniques, ability to digitally manipulate the image contrast and brightness (Figs. 10.4 and 10.5), and cinematic view helping with understanding the flow dynamics.


Fig. 10.2
Plain DCG before digital subtraction


Fig. 10.3
DCG after digital subtraction of the same patient as in Fig. 10.2


Fig. 10.4
Digitally subtracted image with a cannula in left lacrimal system (Photo courtesy: Alkis Psaltis, Adelaide)


Fig. 10.5
Image contrast and brightness manipulation of the same patient as in Fig. 10.4 for better lacrimal delineation (Photo courtesy: Alkis Psaltis, Adelaide)

The technique is performed after cannulating the canalicular system and gently injecting 1 ml of contrast material (Lipiodol, Omnipaque or Gadobutrol) [4]. As the dye is injected, the frames are obtained at a rate of 1 s each. Since the entire lacrimal system would typically fill up in 10 s, frames are obtained for similar duration. During the injection stage, apart from the anteroposterior images, both oblique frontal projections and off-lateral views are captures to yield a better delineation (Figs. 10.6, 10.7, and 10.8). DS-DCG have been reported to not only be useful in detecting presaccal from postsaccal stenosis but also in evaluating results of a dacryocystorhinostomy [5].


Fig. 10.6
Lateral view of DS-DCG showing canalicular filling with dye (Photo courtesy: Alkis Psaltis, Adelaide)


Fig. 10.7
Sequential DCG of same patient as in Fig. 10.6, showing early sac filling (Photo courtesy: Alkis Psaltis, Adelaide)


Fig. 10.8
Sequential DCG of same patient as in Figs. 10.6 and 10.7, showing complete filling of the sac but obstruction at the sac-duct junction (Photo courtesy: Alkis Psaltis, Adelaide)

Dacryoscintigraphy (DSG)

Rossomondo et al. first described the radionucleotide evaluation of lacrimal system in 1972 [7]. The advances in nuclear medicine has made dacryoscintigraphy a fairly safe and easy method for assessing the flow dynamics and other physiological aspects of lacrimal system [69]. It has a complementary role to anatomic studies and can be useful in evaluating pediatric epiphora, partial obstructions, and functional nasolacrimal duct obstructions (Figs. 10.9, 10.10, and 10.11). The test is performed by instilling 10 μl of Technetium 99 pertechnetate into the conjunctival cul-de-sac and tracing the dye through the lacrimal system using a pinhole-collimated gamma camera. Patients are instructed to blink normally and images are acquired in real time up to 30 min. The study end point is the detection of radionucleotide dye in the nasal cavity. In a typical normal DSG, visualization of canaliculi and sac occurs before 30 s and with passage into the nasal cavity in 10–20 min (Fig. 10.9). Areas of interest can be marked on the DSG images and quantity of tracer and times taken can be plotted on the time-activity scales. For example if the system is obstructed at a point, the time-activity slope there would be flat. Disadvantages of DSG include poor anatomical details, poor resolution, and variable transit times throughout the lacrimal system [69].


Fig. 10.9
Dacryoscintigraphy showing a normal right lacrimal system and a left distal canalicular obstruction


Fig. 10.10
Dacryoscintigraphy showing a right presaccal and a left postsaccal obstructions


Fig. 10.11
Dacryoscintigraphy showing bilateral presaccal obstructions (Photo courtesy: Alkis Psaltis, Adelaide)

Ultrasonography (USG)

Lacrimal ultrasonography was first described by Oksala in 1959 [10]. Using the B-scan mode, gross lacrimal anomalies such as diverticula, abscess, and dacryolithiasis could be identified [10, 11]. The normal lacrimal system appears as echo-free tubular structures as compared to a completely filled sac with an echogenic stone or tumor. The advantages of USG are easy technique, can be performed in an outpatient setting, and no radiation exposure. The disadvantages of USG include lack of anatomical details and inability to accurately localize abnormalities. However, with increasing technological improvements, there is a resurgence of interest in lacrimal USG. Determining the DCR ostium size and features in the postoperative period by serial ultrasonic measurements have been reported; however with the advent of endoscopes, a simple outpatient examination with a variety of measuring tools has been favored over a USG [12]. Anatomical and physiological utility of USG biomicroscopy have also been reported to be effective in examining the entire lacrimal drainage system as well as demonstrating the lacrimal sac turbulent flow but has not gained popularity as a clinical tool [11, 13].

Computed Tomography-Dacryocystography (CT-DCG)

Freitag et al. [14] first described CT-DCG in 2002. CT-DCG is an excellent tool for delineating the bony structures around the lacrimal system in bony windows and to some extent soft tissue study of lacrimal system [1, 1517]. Technique employed can be either by dye instillation (drop method) or cannulation technique. The drop method is particularly useful in children and in patients unable to cooperate for irrigation. Serial coronal and axial images (2 mm slices) of the lacrimal area should be requested. Its advantages are listed in Table 10.1. By using modern spiral CT techniques with contrast material, high-resolution thin sections of the system are obtained (Figs. 10.12, 10.13, 10.14, and 10.15). Shorter acquisition time and three-dimensional (3D) reconstruction (Fig. 10.16) offer very good imaging and patient compliance.

Table 10.1
Indications for lacrimal imaging

Mid face trauma

Failed DCR-status of the ostium-size, patency etc.,

Medial canthal masses

Previous lacrimal (failed DCR)/sino nasal surgery

Patients uncooperative to clinical evaluation

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May 26, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Imaging Modalities for Lacrimal Disorders
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