Subcutaneous endometrial deposit: an unusual cause of right iliac fossa pain

A 35-year-old woman presented to hospital with a 7-day history of worsening right iliac fossa pain. The patient reported a 7-month history of intermittent right iliac fossa pain, associated with a palpable nodule in the right iliac fossa. This nodule showed apparent increase in size and tenderness, on palpation, during her menses. Twelve months previously, the patient had undergone a caesarean section. Plain film of the abdomen was unremarkable. Ultrasound examination using a high frequency probe (7.5 MHz) showed a 2 cm nodule in the subcutaneous fat of the anterior abdominal wall superficial to the right rectus abdominus musculature which was hypoechoic relative to adjacent subcutaneous fat and of inhomogenous echotexture with low level internal hyperechoic echoes. Doppler interrogation showed a single vascular pedicle entering the mass at the periphery (Figure 1a). The margins were slightly irregular. There were no ultrasound features of incisional hernia. Computed tomography with intravenous and oral contrast revealed a 2 cm solid, slightly spiculated nodule, located in the subcutaneous fat without involvement of the anterior abdominal wall musculature and parallel to the Pfannensteil incision (Figure 1b). The nodule was hyperdense compared to rectus abdominus musculature following intravenous contrast enhancement, measuring approximately 80 Hounsfield units. There was minimal stranding of the surrounding subcutaneous fat. Differential diagnosis included haematoma, abscess, sebaceous cyst, enlarged lymph node, desmoid tumour, and malignant tumours such as malignant melanoma, or metastatic breast or renal cell carcinoma. Percutaneous biopsy using a 17 gauge coaxial needle system was performed under ultrasound guidance (Figure 2a). Histopathological examination confirmed endometrioma (Figure 2b).