Hematongenous soft tissue metastases seldom occur but are seen from lung carcinoma, renal carcinoma [
2,
3]. Intraneural metastasis from carcinoma is extremely rare. A few cases were reported including mammary carcinoma [
4], lymphoma [
4], renal carcinoma [
5], and melanoma [
6]. To the best of our knowledge, this report is the first description of a case of sciatic nerve palsy due to intraneural metastasis of gastric carcinoma.
Soft tissue metastasis including the muscles, tendons, ligaments, subcutaneous tissues, skin and nerve is very rare compared to lungs, liver, bones and lymph nodes. Several factors have been implicated in the rarity of soft tissue metastasis such as changes in pH, accumulation of metabolites, and local temperature at soft tissue sites [
7] The organs with high frequency of metastasis are rich in capillary vessel and have a constant flow, whereas in soft tissue blood flow is variable and is influenced by adrenergic receptors and is subject to varying tissue pressure that may affect tumor implantation [
7-
9]. Another reason of rarity of intraneural metastasis by carcinoma is existence of ‘blood-nerve barrier’ which, similar to the blood–brain barrier, may prevent implantation of tumor cells by vascular channels [
10].
Sciatica is a common condition, affecting as many as 40% of adults at their lives [
11] and continual sciatica can finally result in sciatic nerve palsy. Although sciatica is usually caused by lumber disc hernia and lumber canal stenosis, it is not often but we should consider the nondiscogenic sciatica, which can be categorized as either intrapelvic and extrapelvic [
11]. The causes of extrapelvic include aneurysms or pseudoaneurysms of gluteal artery [
12-
14], tumors [
15], gluteal abscess [
16], avulsion fracture of the ischial tuberosity [
17], and paralabral cysts [
11]. There are three ways by which tumor can influence the functional and structural integrity of nerve tissue; (1) the tumor can stretch the nerve trunk by pushing it without invading the sheath; (2) the tumor can compress or strangulate the nerve by engulfing it without genuine invasion of the sheath; (3) the tumor can perforate the nerve [
10,
18]. Our case is consistent with (3) because MRI, Macroscopic findings, Histological examination and clinical behavior totally supported the fact that metastatic gastric carcinoma directly invaded sciatic nerve and spread the surrounding muscles. Based on these findings, we concluded the cause of sciatic nerve palsy is not the invasion of soft tissue metastasis but direct intraneural metastasis.
Treatments including radiotherapy, chemotherapy and surgical excision are controversial [
2] because prognosis for patients with soft tissue metastasis is poor and mean survival was only 8.4
months [
3]. This is why the management of the soft tissue metastasis including intraneural metastasis depends on the clinical setting and the condition of the patients. In our case, although the patient was elderly, our decision for treatment was base on the below facts, 1) primary site was completely cured 2) no evidence of other site metastasis by CT 3) good general condition 4) possibility the mass could get larger and more painful in short time. Especially in the case of intraneural metastasis, surgical excision seems to be the only option [
4-
6] but we should be careful because of two opposite reasons 1) reductive excision means the higher rate of recurrence 2) curative excision means the larger damage and loss. Usually it is very difficult to decide which is harmless for patients, curative or reductive. In our case, we could easily emphasize the less recurrence induced by curative excision because sciatic nerve had already paralyzed. Our patient has benefitted from excision to provide the free survival but we should absolutely consider the two previous facts, 1) the success to prolong survival has been reported anecdotally after excision of solitary soft tissues masses from only renal [
19] and, rarely, lung primaries [
7]. 2) In addition, excision of lung and colon soft tissue metastases led to rapid local recurrence, regional lymph node spread and resulted in widespread dissemination of disease and death in short order [
20-
22].
1 Takashi Shimoji,1 Taisuke Tanizawa,1 Tabu Gokita,1 Keiko Hayakawa,1 Kaoru Aoki,1 Saori Ina,1 and Hiroaki Kanda2
publication history
