Imaging Features of Malignant Lacrimal Sac and Nasolacrimal Duct Tumors

Discussion

To our knowledge, no large imaging series has assessed malignant lacrimal sac and nasolacrimal duct tumors. This report highlights the CT and MR imaging features and spread pattern of these tumors. In our series, the most common tumor histology was SCCA (39%), which has also been reported in other studies.^5,6 Eighty-three percent of primary and secondary tumors in our study involved both the lacrimal sac and nasolacrimal duct at the time of initial imaging. The medial canthus region (Figs 2 and 3) was commonly involved by malignant tumors (89%) because of direct tumor spread from the lacrimal sac; intraconal orbital extension of tumor was less common (11%). The differential diagnosis of masses in the medial canthus includes lacrimal sac and duct neoplasms, but more commonly, dacryocystitis or idiopathic nasolacrimal duct blockage is a cause.⁵ In our series, 38% of the primary malignant nasolacrimal sac or nasolacrimal duct tumors demonstrated spread to either the sinus or nasal cavity.

Tumor abutted the infraorbital foramen in 2 patients with advanced disease. However, perineural tumor spread along the infraorbital nerve was not seen on imaging or on histology. Intracranial tumor extension or distant metastases were not observed in any patient at the time of diagnosis. Nodal metastasis was seen in only 1 patient in our series. In a large ophthalmology study, Ni et al⁷ found distant metastases from malignant lacrimal sac tumors in only 6/74 patients and intracranial tumor spread in 1/74 patients. They found nodal metastasis in 28% of patients, generally months to years after the initial diagnosis.⁷ When present, nodal metastases from malignant lacrimal sac and duct tumors generally involve the preauricular, submandibular, and cervical lymph nodes.^7,8

In 69% our cases imaged with CT, the malignant lacrimal sac and duct tumors expanded the lacrimal bony canal (Fig 5B) without erosion. CT was superior to MR imaging in the delineation of the lacrimal bony canal and in evaluating expansion versus erosion of the canal. Thin-section coronal imaging was very helpful on both CT and MR imaging in the interpretation of the study because it nicely displayed the entirety of the lacrimal sac and duct and regional tumor spread (Fig 4A). When postobstructive sinus secretions were present (3 cases), MR imaging was superior to CT in distinguishing tumor from secretions within the sinonasal cavity. In 2 cases, MR imaging and CT were equivalent in the diagnostic evaluation of intraconal tumor spread. We found that the lacrimal canaliculi were not easily identifiable on MR imaging and CT, due to the small size of these anatomic structures. In cases of locally advanced malignant lacrimal sac and duct tumors, we found it difficult to distinguish primary tumors from secondary tumors by imaging. We anticipated seeing dacryocystocele formation secondary to tumor obstruction of the nasolacrimal duct more frequently; however, this was not seen in any case.

In most cases in this study, the malignant lacrimal sac and nasolacrimal sac tumors demonstrated moderate contrast enhancement on CT and MR imaging and demonstrated isointense signal intensity on T1-weighted and T2-weighted MR imaging. Contrast enhancement and MR imaging signal intensity were not helpful in distinguishing tumor histology, except in 1 case of recurrent nasal cavity melanoma, which spread to the nasolacrimal duct and demonstrated high T1WI signal intensity. Primary malignant melanoma of the lacrimal sac is rare, accounting for only 5% of lacrimal sac tumors.⁹ Due to the paramagnetic properties of melanin, melanoma may appear hyperintense on T1WI and hypointense on T2WI.⁶ According to Billing et al, ⁹ melanoma may also demonstrate isointense T1WI and T2WI signal on MR imaging (Fig 3A, -B).

Treatment of primary malignant lacrimal sac and nasolacrimal duct tumors typically involves wide local resection, followed by radiation and/or chemotherapy. In our series, surgical excision of the lacrimal sac was complemented by a medial maxillectomy to allow complete resection of the nasolacrimal duct. Judicious use of postoperative adjuvant proton radiation therapy or concurrent chemoradiation therapy can yield good local/regional control, and a globe-sparing surgery can be achieved in most cases with reasonable visual outcomes.⁵ Bony erosion of the nasolacrimal bony canal does not portend a worse prognosis, but it may dictate the size of the planned bony resection, which, in addition to a medial maxillectomy, may also include an ethmoidectomy. Larger tumor diameter (generally >30 mm) at the time of presentation⁵ and tumor invasion of the intraconal space of the orbit may necessitate orbital exenteration (Fig 4A, -B).

Imaging surveillance of the head and neck is recommended every 3 months for the first year, every 6 months the second year, and annually in the third year and beyond.⁵ On the basis of the results of this study, the authors recommend performing a thin-section (1.25 mm) CT with contrast as the first-line imaging study to evaluate malignant lacrimal sac and nasolacrimal duct tumors at the time of initial staging. MR imaging can be performed if CT cannot distinguish sinonasal tumor extension from postobstructive secretions.