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A case of primary malignant melanoma of the lacrimal sac is presented. This is the first report of the preoperative magnetic resonance imaging (MRI) findings of malignant melanoma of the lacrimal sac.
A 54 year old Chinese woman was referred to an ophthalmologist complaining of a 6 month history of left sided bloody tears and epistaxis. She had a firm, non-tender left medial canthal swelling, and syringing revealed left nasolacrimal duct (NLD) obstruction. Ocular and periorbital examination was otherwise normal. A dacryocystogram (DCG) demonstrated a filling defect in the lacrimal sac with NLD obstruction.
An ENT opinion was sought, and nasal examination revealed left sided septal deviation, with no obvious cause for the epistaxis.
Computed tomography (CT) of the head and orbits demonstrated a left lacrimal sac lesion extending into the NLD with proximal dilation of the duct and no apparent bone erosion (Fig 1A) MRI confirmed the presence of a lacrimal sac lesion with intermediate signal intensity on T1 and T2 weighted images (Fig 2A, B) The lesion enhanced with intravenous gadolinium.
An incisional biopsy of the lacrimal sac (Fig 1B) under frozen section control, and paraffin sections, confirmed malignant melanoma.
A full medical review, including MRI of the chest and abdomen, and liver function tests, excluded tumour elsewhere. However, abdominal MRI and ultrasound revealed a co-incidental polycystic liver.
Three weeks after biopsy, a wide local excision including the medial upper and lower eyelids, dacryocystectomy and medial maxillectomy was performed. A tumour, confined to the sac, and invasion through the medial wall of the upper NLD, into the lateral wall of the nose, and apposing nasal septal mucosa, was seen peroperatively and confirmed histologically.
She underwent postoperative adjuvant radiotherapy (55 grays) and to date, 4 months later, remains well.
Malignant melanoma of the lacrimal sac is rare accounting for 5% of lacrimal sac tumours.1,2 It has an unfavourable prognosis compared with other causes of lacrimal sac tumour, and is considered more aggressive than cutaneous malignant melanoma.2,3 Response to treatment is generally poor, with up to 80% of cases recurring within 2 years.
Radiological features of lacrimal sac tumours include filling defects on DCG and mass lesions on CT.1–3 However, to the authors’ knowledge, this is the first report of the MRI findings of malignant melanoma of the lacrimal sac.
Owing to the paramagnetic properties of melanin, malignant melanoma appears hyperintense on T1 weighted imaging, and hypointense on T2 weighted imaging.4 A study of six mucosal melanomas of the head and neck found that on T1, five lesions were hyperintense and one was isointense.5 On T2, five were of mixed intensity and one was isointense. They concluded that hyperintensity on T1 of mucosal melanomas was characteristic but not universal.
The majority of malignant lacrimal sac tumours are epithelial in origin.3 Imaging features suggesting malignancy include invasion of bone, rapid growth, and irregular margins with skin fixation. On MRI, the majority of epithelial tumours have intermediate signal intensity on T1 and high T2 signal intensity. High tumour cellularity is associated with intermediate to low T2 signal intensity.6
High signal intensity on T1 is not specific for malignant melanoma. Subacute haemorrhage caused by the presence of methaemoglobin is more likely and although melanoma may undergo intratumoral haemorrhage, other tumours with a tendency to bleed include small cell lung carcinoma, choriocarcinoma, and renal cell carcinoma metastases.7 Less likely causes include fat containing tumours (lipoma, dermoid, and teratoma) requiring MRI fat suppression methods,6 paramagnetic material (manganese, iron, and copper), and very high (non-paramagnetic) intratumoral protein concentration.
MRI has been reported as a useful investigative tool in the assessment of lacrimal disease owing to its ability to delineate soft tissues. Intravenous and intracanalicular gadolinium adds useful information on lesional enhancement and lacrimal apparatus structure and function.8 The predictive value of MRI for lacrimal sac melanoma, however, appears to be variable. Hyperintensity on T1 relies on the paramagnetic properties of melanin, the presence of which is variable in amelanotic melanoma. This is supported by our case, where only moderate T1 hyperintensity with contrast enhancement was demonstrated.
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