INTRODUCTION

Vulvar cancer is the least common tumour of the female genital tract (3-5%) and occurs mainly in post-menopausal women. Most patients are diagnosed at an early stage, due to the presence of vulvar swelling or ulceration associated with symptoms (pain, itching, discharge, etc.) or debut with palpable inguinal lymphadenopathy. While approximately one third of patients with vulvar carcinoma are diagnosed with locally advanced disease at the time of presentation, there is currently no protocol for the management of vulvar carcinoma. There is currently no protocol for the detection or screening of vulvar carcinoma, with most being diagnosed when the patient presents clinically. The treatment and prognosis of the disease is determined by its stage at diagnosis, with inguino-femoral lymph node involvement being the most decisive factor in terms of survival. Imaging techniques play an important role in the staging of the tumour, which is essential for the selection of candidates for surgery, with the aim of reducing morbidity and increasing survival in these patients.

ANATOMY OF THE VULVA AND LYMPH SYSTEM

The vulva is a triangular structure delimited externally by the skin and in depth by the urogenital diaphragm. The symphysis pubis is located anteriorly and the anal sphincter posteriorly, and on either side are the ischial fossae.It is formed by the following structures: mons venus, labia majora and minora, clitoris, vestibular bulb, spongy bulb, ischicavernosus muscles and the vestibule, which contains the urethral meatus and the vaginal introitus (Figure 1).

Approximately 70% of cancers occur in both the labia majora and minora, 15-20% of cases to the clitoris, and in 10% the primary location cannot be determined due to the extent of the lesion. In 5% of cases the lesion is multifocal. 

The vulva is supplied by external and internal branches of the pudendal artery and vein, draining also through the perineal and posterior deep clitoral veins.

The regional lymphatic drainage of the vulva is through the superficial inguinal nodes and subsequently through the deep inguinal nodes (Figure 2). The inguinal nodes are located inferior to the inguinal ligament and the external iliac nodes. 

- The superficial inguinal ganglia are located deep to the inguinal ring and can be divided into three groups: the superficial medial group, the superficial intermediate or vertical group and the superficial lateral group. The most important are the saphenofemoral junction ones, where the sentinel node usually drains. 

- The deep inguinal (deep femoral) nodes are located medial to the femoral vein, and drain to the external iliac nodes.

Lateral vulvar carcinomas drain into the ipsilateral inguinal nodes whereas if located at or within one centimetre of the midline they may drain bilaterally due to the rich lymphatic network in this region. Deep inguinal nodes may be involved even if superficial inguinal lymph nodes are not. 

Pelvic lymph nodes (considered metastatic) are rarely involved unless the ipsilateral inguinal nodes are involved. If lymphatic drainage is obstructed, the tumour may spread through the subcutaneous and dermal lymphatic vessels of the upper thigh and lower abdomen.

Survival depends on the status of the lymph nodes. Patients with negative lymph nodes have a 5-year survival of 90%, while survival is reduced to 50% in patients with positive lymph nodes.

Vulvar carcinomas generally have a squamous cell lineage (85-90%; the remaining 10% are melanomas, basal cell carcinomas, sarcomas and adenocarcinomas). Furthermore, they can be divided into those that are related to human papillomavirus infection (young women, 20%) and those that are not (older patients, 80%). In premenopausal women it is more likely to be associated with HPV 16 or 18 infection and may present with multicentric disease.

IMAGING DIAGNOSIS

Imaging techniques are reserved for cases where clinical examination shows evidence or suspicion of involvement of surrounding perineal tissues or if the medial structures are infiltrated and/or there is high suspicion or evidence of lymph node invasion, with MRI specifically being the imaging technique of choice.

MRI has high soft tissue resolution and high sensitivity in lymphatic evaluation. It also plays a role in specific treatment planning such as RT in vulvar carcinoma, and is widely accepted in the assessment of tumour response after multimodality treatment. However, the usefulness of MRI in the evaluation of primary tumours ≤2 cm, confined to the vulva and/or perineum, and with ≤1 mm of stromal invasion is not clearly established and is therefore not recommended in these cases. 

The classic definition of locally advanced vulvar carcinoma (LAVC) includes:

A. Large (>4 cm) primary tumours invading adjacent perineal organs.

B. Tumours presenting with bulky inguinal lymphadenopathy, which may be attached to fascia, muscle or vessels.

C. Tumours that cannot be managed with radical vulvar resection.

The most commonly used staging system for vulvar cancer is that developed by the International Federation of Gynaecology and Obstetrics (FIGO). According to this system, stages IIIA and IVA are considered LAVC. 

MRI IN THE STAGING OF LAVC

- Indications:

For primary tumours ≤2 cm, confined to the vulva and/oror perineum, and with ≤1 mm of stromal invasion, imaging staging is not recommended. Pelvic MRI including the inguinal regions should be performed for local staging of vulvar cancer with stromal invasion >1 mm, tumour size >4 cm or tumours with suspicious involvement of the urethra, vagina or anus based on clinical assessment.

For tumours >2 cm and ≤4 cm, clinical staging and groin ultrasound (with puncture of suspicious lymph nodes) or MRI staging are considered valid options.

For regionally or locally advanced disease (FIGO stage III-IVA) or suspicious distant metastases (FIGO stage IVB), a CT scan of the chest, abdomen and pelvis (or PET/CT) with coverage of the groin regions should be performed.

- Protocol:

1. Patient preparation: Fasting (4-6 h) and administration of antispasmolytic agents (20 mg butyl scopolamine IM/IV or 1 mg glucagon IV) is recommended. The bladder should be emptied prior to the study. Vaginal opacification with gel is optional. Rectal gel is not recommended.

2. Software: The minimum magnetic field strength for staging vulvar cancer is 1.5T. 

3. Sequences and imaging planes: (Figure 3)

T1WI images: Dixon axial sequences.

T2WI images: Axial, sagittal and coronal two-dimensional sequences. Recommended thickness less than 4 mm.

• Recommended with reduced field of view (rFOV) as it increases spatial resolution and allows for better anatomical detail. They can be obtained with oblique plane (perpendicular to the urethra) and oblique coronal plane (parallel to the urethra). It should cover from the vaginal crest to the entire perineum including the perineum with a slice thickness of 3 mm.

Optional:

T2WI imaging with fat suppression.

DWI-MR imaging: in axial with minimum b-values (b under 0-50 or 100 s/mm2). T2WI and DWI-MR should have the same acquisition plane, field of view and slice thickness to allow parallel interpretation and/or image fusion. 

DCE-MR images in three-dimensional 3D fat-suppressed T1-weighted 3D sequences (3D T1WI FS) in axial or oblique axial before and after IVC administration for three scans to obtain arterial, portal and equilibrium phases.

To assess the upper abdomen (kidneys and lymph nodes):

T2W HASTE axial from renal hilar to inguinal region

DWI axial from the renal hilar to the inguinal region

- Imaging:

Vulvar tumors are usually seen as intermediate intensity lesions on T2-weighted and hypointense T1-weighted sequences. In DWI, they may present moderate to high restriction, and after contrast administration they enhance early in an avid manner, this sequence being very useful for assessing both their real dimensions and their extension to neighbouring organs. 

On the other hand, lymph nodes that are affected by lymphatic spread will show a moderate T2 signal with DWI restriction and contrast hyperenhancement. Other signs suggesting lymphatic involvement are based on the size and morphology of the adenopathy, showing a size greater than 1 cm in its short axis or the presence of irregular borders, loss of fatty hilum or central necrosis. It is important to note that there may be false positives if the MRI is performed too soon after the biopsy, and it is recommended to wait after the biopsy. 

We provide examples from our centre:

Case 1 (Figure 4-5)

Case 2 (Figure 6)

Case 3 (Figure 7-8)

Case 4 (Figure 9)

Case 5 (Figure 10-11)

Case 6 (Figure 12-13)