Teaching Case

An 81-year-old female with a history of left mastectomy 4 years prior for invasive breast cancer (IDA G2pT1cN1a (se);ER 8/8, PR 6/8,ISH-;KI67 intermediate). Aromatase inhibitor therapy was initiated. Because of comorbidity and cardiomyopathy, radiotherapy was not administered, despite sentinel node metastasis.

Previous follow-up imaging was normal.

Clinical examination was unremarkable.

Sonographic examination of the mastectomy scar showed a small oval hypo-echoic subcutaneous nodule of 6 mm with sharp delineation, smooth regular margins and no intralesional vascularisation on power-Doppler ultrasound.

The lesion was parallel oriented to the chest wall. (Fig.1)

Ultrasound-guided biopsy (Fig.2) and subsequent histopathological investigation

( Fig.3a and 3b) revealed a neuroma.

A traumatic neuroma is a rare benign lesion occurring in a mastectomy scar after breast surgery.

It consists of a benign proliferative lesion as a response to nerve injury, caused by direct or indirect trauma, surgery or chronic inflammation. On immunohistochemical examination, the lesion is composed of bundles of nerve cells with degenerative changes surrounded by fibro-adipose tissue. The nerve cells are positive for S100 protein and have a typically brown colour on immunohistochemistry.[1,2]

The lack of pankeratin and KI 67 expression on immunohistochemical examination excludes proliferation activity and malignancies such as carcinoma or sarcoma.[1,2,3]

Usually, the patient is asymptomatic and the lesion is often detected at the mastectomy scar on follow-up ultrasound after mastectomy.[1,2,3]

On ultrasound, the lesion often shows a benign morphology, with smooth regular margins, sharp delineation and homogenous hypoechoic appearance. Color Doppler images show no internal vascularity.[3]

Magnetic Resonance Imaging (MRI) was not performed in this patient, but MRI findings are often non-specific: on dynamic T1 contrast-enhanced MRI sequences the nodule shows most commonly a type I or type II kinetic curve, although a type II curve with wash-out has also been described. According to the literature, a neuroma has often an isointense signal on T1–weighted images and a high signal intensity on T2-weighted images. [4,5]

Although the lesion has a nonaggressive morphology and may mimic a benign lesion such as an oil cyst, any lesion appearing in a postoperative scar should be interpreted with caution. Therefore malignancy should be excluded by means of biopsy and subsequent immunohistological examination.

Treatment or surgery for a neuroma is not required and watchful waiting and annual follow-up ultrasound is recommended.[1]

Take-home messages

A neuroma is a rare benign lesion, seen in patients with a previous mastectomy.

The clues to the correct diagnosis are the awareness of the clinical history, the presence of a well-defined hypoechoic nodule at the mastectomy scar on ultrasound

and the presence of nerve fibres on immunohistochemistry.