nerve root compression caused by degenerative disc disease around the spinal column is a common cause of radiating pain to the lower extremities9 ) . radiating pain of extraspinal origin can be easily overlooked and may be difficult to discriminate from radiculopathy caused by spinal disease and plexopathy in the pelvic area , distracting from the neurological diagnosis of a lower extremity problem . we herein describe a patient who underwent spinal surgery to treat sciatica but was finally diagnosed with late recurrence of colorectal cancer in the presacral area . a 54-year - old man with sciatica in the left buttock and posterior aspect of the left leg visited our outpatient clinic . he had undergone laminectomy and discectomy after diagnosis of lumbar stenosis at another hospital when the symptoms had developed 8 months prior . preoperative lumbar magnetic resonance imaging ( mri ) revealed mild disc protrusion at l4/5 ( fig . 1 ) . lumbar mri 2 weeks postoperatively revealed a well - decompressed thecal sac ( fig . the motor power of the lower extremities was intact on neurological examination , but disabling pain was aggravating the left fourth lumbar to first sacral dermatome . the pain was constant and was not relieved by postural change . because the sciatica did not improve and was even becoming aggravated , he underwent three additional lumbar mri examinations at different hospitals . although he had a history of colon cancer surgery 7 years prior , he did not report this history to the spinal surgeon or medical personnel because he had been told that the colon cancer had completely remitted 5 years after the colorectal surgery . we performed enhanced pelvic mri , which revealed a heterogeneous , well - enhanced mass compressing the lumbar plexus at the anterior aspect of the left sacrum . the lobulating mass was suspected to be a metastasis of colon cancer to the presacral lymph node ( fig . an abdominal pelvic computed tomography scan also revealed a heterogeneously enhanced mass destroying the sacral bone of the left pelvic wall ( fig . 4 ) . colonoscopy revealed no evidence of cancer recurrence at the colonic anastomotic site ; only benign polyps were apparent . f - fluorodeoxyglucose positron emission tomography - computed tomography also revealed an enhanced mass ( standardized uptake value , 2.1 ) with cortical invasion of the sacrum ( fig . 5 ) . the carcinoembryonic antigen level was elevated at 16.44 ng / ml ( reference range , 0.0 - 4.7 ng / ml ) . the recurrent mass was severely adhered to the lumbar plexus in the presacral area ( fig . a metastatic lesion in the deep pelvic area could not be removed completely because of massive bleeding from the deep pelvic venous plexus . immunostaining for ck20 and cdx2 was positive , and the k - ras mutation ( codon 12 p.g12d ) was present . the patient underwent chemotherapy and adjuvant radiation therapy under a final diagnosis of recurrent colon cancer at the presacral lymph node . the lumbar plexus comprises t12-l5 and the sacral plexus of the s1 - 5 nerve roots . demyelinating disease , a neoplasm , an inflammatory lesion , post - partum status , diabetes , osteoarthritis , and radiotherapy are reported extraspinal causes of plexopathy2451112 ) . it is difficult to clinically discriminate between radiculopathy caused by spinal disease and plexopathy from the pelvic area . nineteen patients had malignant bone tumors in the lumbar spine or pelvis , and 10 had symptoms of degenerative disc disease . the same errors continue to be made despite the fact that today 's diagnostic tools are much more advanced . indeed , several case reports on unnecessary spinal surgery seeking to treat radiating pain , which was ultimately identified as being of extraspinal origin , have been published recently713 ) . radiculopathy caused by spinal disease may be intermittent or constant , and may worsen with increased intra - abdominal pressure ( as when coughing ) . the pain may be relieved in the supine position , which decreases pressure on the herniated disc , and is aggravated by sitting , bending , or prolonged standing . stretching the nerve reproduces pain in the sciatic distribution ; this is the so - called " lasegue sign"6 ) . bickels et al.3 ) reported that a particular pain pattern was the single most common finding in patients with extraspinal tumors . in patients with neoplastic plexopathies , pain onset is usually insidious , prominent in one leg , and often the initial symptom of disease1 ) . an early diagnosis is possible if the pain pattern is insidious in onset , constant , progressive , and unresponsive to changes in position . if a patient has underestimated lumbosacral plexopathy combined with asymptomatic radiological stenosis , the surgeon may make a wrong decision ; lumbar spinal surgery is unnecessary . it is difficult to accurately distinguish spinal from retroperitoneal or pelvic diseases using radiology alone ; the imaging characteristics are nonspecific . such clinical scenarios , coupled with imaging , should be contemplated by both the spinal surgeon and radiologist , who need to recognize that a non - spinal lesion is possible11 ) . in the present case , the principal reason for failure of an initial diagnosis of metastatic lymphadenopathy was that the cancer was of low signal intensity on t2-weighted images , inviting confusion with a part of the paravertebral muscle , particularly on sagittal images . another reason is that the initial mri protocol did not include contrast - enhanced mri , which highlights a lesion . it is difficult to trace the lumbosacral plexus via two - dimensional mri ( the orientation of which is oblique ) . some authors have attempted to trace the plexus using three - dimensional short - tau inversion recovery reconstructions in the coronal oblique plane through the plexus1 ) . although we did not perform electrodiagnosis , this modality , coupled with nerve conduction studies and needle electromyography , can help localize and characterize the underlying cause of a neurological condition in the absence of any invasive procedure8 ) . . however , an electrophysiological study does not feature in routine evaluations prior to spinal surgery , which may be a serious error if a patient has symptoms that can not be matched with radiological data . lumbosacral plexopathy is a severe clinical syndrome that is very likely to be underdiagnosed because of confusion with lumbosacral disc disease . this case report emphasizes the importance of obtaining an accurate history and careful performance of a neurological examination to differentially diagnose lumbar plexopathy from degenerative lumbar disease . a spinal surgeon should always consider an extraspinal origin of sciatica arising from the pelvis , particularly in a patient with symptoms that are not explained by imaging .
radiculopathy triggered by degenerative spinal disease is the most common cause of spinal surgery , and the number of affected elderly patients is increasing . radiating pain that is extraspinal in origin may distract from the surgical decision on how to treat a neurological presentation in the lower extremities . 
 a 54-year - old man with sciatica visited our outpatient clinic . 
 he had undergone laminectomy and discectomy to treat spinal stenosis at another hospital , but his pain remained . 
 finally , he was diagnosed with a plexopathy caused by late recurrence of colorectal cancer , which compressed the lumbar plexus in the presacral area . 
 this case report illustrates the potential for misdiagnosis of extraspinal plexopathy and the value of obtaining an accurate history . 
 although the symptoms are similar , spinal surgeons should consider both spinal and extraspinal origins of sciatica .