We present the case of an 8-year-old boy who underwent an above-knee amputation after chemotherapy for an osteosarcoma of the right distal femur. The patient was asymptomatic and had routine follow-up MRIs of the lower extremities at three and six months after amputation to rule out local tumour recurrence.
MRI (Avanto Siemens 1.5T) revealed a tubular hyperintense structure seen on STIR images, extending from the transection site to the level of the proximal femoral metaphysis, corresponding to a thickened right sciatic nerve. The enlargement was more significant distally and tapered proximally. No thickening was seen on the contralateral side and no focal enhancement of the nerve was noted on contrast-enhanced images. The sciatic nerve hypertrophy was absent on the preoperative MRI (Fig. 1a-b), appeared on the 3-month follow-up MRI (Fig. 2a-b) and seemed to have increased on the 6-month MRI (Fig. 3a-b). No evidence of tumour recurrence was observed.
Paradoxic sciatic nerve hypertrophy may be observed after leg amputation particularly in young patients [1] but also in adults [2]. It is considered paradoxic because one would expect the nerve proximal to the amputation site to become atrophic as demonstrated in investigations of nerve reactions to axotomy in humans and in animals [3]. The physiopathology of paradoxic hypertrophy is still not well understood due to the lack of histological evidence. One of the hypotheses suggested in the literature is that nerve enlargement could be due to an alteration in the normal cellular response in which neurofilaments continue to be synthesized and transported after nerve transection leading to their accumulation [2]. Osteosarcomas are known to synthesize trophic factors such as an insulin-like growth factor, which may play a role in nerve enlargement [4]. According to the literature, nerve hypertrophy seems to increase in relation with the time elapsed since amputation as observed in our patient [3]. A differential diagnosis to mention is a stump neuroma which is rather a more focal nodular enhancing mass at the transection site. In our patient the nerve was enlarged globally and there was no focal distal enhancing mass of the nerve.
It is important to recognize a paradoxic sciatic nerve hypertrophy and to distinguish it from neuroma or local tumoral recurrence, to avoid unnecessary biopsy. The patients with this pathology are asymptomatic and do not require treatment [3].
Post-amputation paradoxic hypertrophy of the sciatic nerve
Based on the provided MRI images, the following main features can be observed:
Considering the patient's history (8 years old, right distal femoral osteosarcoma treated with amputation and chemotherapy) and the current MRI findings, the following diagnoses or differential diagnoses are primarily considered:
Based on the patient’s past osteosarcoma history, post-operative status, current absence of significant symptoms at follow-up, and MRI findings of diffuse sciatic nerve thickening without nodular or enhancing lesions, the most consistent diagnosis is:
Paradoxic Sciatic Nerve Hypertrophy.
The diagnostic basis includes:
Treatment Strategy:
Rehabilitation Training and Exercise Prescription (FITT-VP principle) Example:
Throughout training, monitor the residual limb and nerve condition closely. If sudden nerve pain or increased swelling occurs, training should be paused, and medical evaluation is recommended. For pediatric patients post-osteosarcoma surgery, regular follow-up is essential to ensure safe rehabilitation and promptly detect any potential tumor recurrence.
Disclaimer: The above report is based solely on the provided examination images and clinical history for reference and does not replace in-person consultation or professional medical advice. If you experience discomfort or have concerns, please consult an orthopedic, oncology, or rehabilitation specialist for further evaluation and treatment.
Post-amputation paradoxic hypertrophy of the sciatic nerve
