Clinical History
63-year-old woman presented with vaginal rash and a palpable nodule of the vulva. At physical examination an exophytic pigmented lesion was observed in the lower third of the vagina.
Imaging Findings
An abdominal and pelvic MRI with intravaginal contrast (ultrasound gel) was performed to further characterise and depict the extent of the vaginal lesion.
This study demonstrated an exophytic lesion with a lobulated contour, arising from the anterior and lateral wall of the lower third of the vagina. The lesion showed homogeneous intermediate signal intensity – slightly higher than muscle – and a small high signal intensity spot on T1-WI (Fig.1). On T2-WI the lesion showed homogeneous intermediate/high signal intensity – higher than muscle, lower than fat (Figs.2-4). On T2-WI it is also possible to observe invasion of the inferior segment of the urethra (Fig.4). After the administration of gadolinium the tumour shows homogeneous enhancement (Fig.5). The axial diffusion-weighted image (b=600 sec/mm2) shows the vaginal mass with bright signal intensity (Fig.6).
An anterior pelvic exenteration was performed, removing the uterus, adnexa, bladder, urethra and vagina. The gross specimen showed a pigmented lesion (Fig.7).
Discussion
Primary vaginal malignant melanoma corresponds to less than 3% of all vaginal malignancies [1], being more common in the postmenopausal woman.
Primary vaginal melanoma may arise anywhere in the vagina but there is a predilection for the lower third and for the anterior and lateral walls [2].
The macroscopic characteristics usually suggest the diagnosis at physical examination. Malignant melanoma is usually pigmented but may be devoid of pigment (amelanotic melanoma) and can contain both pigmented and nonpigmented lesions in a zosteriform pattern [2], with ulceration and necrosis being usually present.
The melanotic type classically demonstrates intermediate to high signal intensity on T1-weighted imaging due to the paramagnetic effect of melanin and methemoglobin from intratumoral haemorrhage, with corresponding low to intermediate signal intensity on T2-weighted imaging.
Many primary malignant melanoma of the vagina do not present with these typical features on MRI, showing high to intermediate signal intensity on T1- and T2-weighted images.
Amelanotic melanomas show low signal intensity on T1-weighted images and intermediate to high signal intensity on T2-weighted images [2].
Therefore, the absence of high signal intensity on T1-weighted images should not exclude the diagnosis of malignant melanoma.
Differential Diagnosis List
Primary malignant melanoma of the vagina
Squamous cell primary vaginal carcinoma
Vaginal metastases
Vaginal lymphoma
Vaginal leiomyosarcoma
Final Diagnosis
Primary malignant melanoma of the vagina
