SEL is a condition wherein excess adipose tissue deposits around the thecal sac causing compression of neural structures2,3,5,7,8,12,17,18,24,31,32)
. In 1975, Lee et al.18)
reported the first case of symptomatic epidural cord compression secondary to SEL. It is well known that the main etiological factors of SEL are associated with endocrine dysfunction such as Cushing disease, hypothyroidism, obesity, iatrogenic steroid treatment for immune disorders, COPD and transplantation9,11,20,27)
. In approximately 75% of SEL, this may be secondary to exogenous steroid administration for systemic diseases such as rheumatoid arthritis, systemic lupus erythematous, dermatomyositis, chronic obstructive pulmonary disease, or following organ transplantation27)
. Obesity is the second most common associated category of SEL5,9,11)
Idiopathic SEL was first reported by Badami and Hinck3)
in 1982. Haddad, et al.12)
first hypothesized that idiopathic SEL was a byproduct of obesity, with the gradual overgrowth of epidural fat resulting in compression of the spinal cord and nerves. Thereafter, several researchers asserted that the term 'idiopathic' should be used solely to characterize cases of SEL that develop in non-obese patients, who were not receiving corticosteroid therapy, and without any other underlying SEL-related disease such as hypothyroidism or endogenous corticosteroid production4,6,9,19)
. About 16 cases of idiopathic SEL in non-obese patients were reported previously1,9)
. The underlying pathological mechanism of SEL is still unknown.
Our patient was neither receiving steroids nor had any kind of endocrinopathy. Moreover, she was not obese. For this reason, we had difficulty diagnosing idiopathic SEL as the cause of chest pain.
The majority of idiopathic SEL involve the mid-thoracic and lower lumbar vertebral levels, representing two peaks9,15)
. SEL causing neurological deficits occurs more frequently in the thoracic than the lumbar spine17,23)
. Patients may present with progressive and long standing complaints of pain, weakness, numbness, incontinence, ataxia, abnormal reflexes and rarely paralysis. According to Al-Khawaja et al.2)
, patients with idiopathic SEL involving the thoracic segments had myelopathy in 70% and paraplegia in 5% of patients. All of these symptoms were induced by compression of the spinal cord. In cases of lumbar SEL, symptoms associated with lumbar radiculopathy were reported but thoracic radiculopathy has not been reported1,4,8,9,30,34)
The mechanism of SEL induced neurologic symptom is mainly by direct compression of the adjacent nervous structures and epidural blood vessels resulting in venous engorgement which then compromise contribute to the evolution of myelopathic and radicular complaints1,30)
. We identified the direct compression by the lipomatous tissue and with venous engorgement around the DRG during the operation and believed that these findings induced the radiculopathy with intractable chest pain and paresthesia. The DRG is exquisitely sensitive to direct pressure and can generate prolonged neural discharges even after brief compression. The nerve root itself responds to this same stimulus only after it has become inflamed and sensitized14,33)
. These features of the DRG are thought to be the cause of intractable pain in our case.
Symptoms and signs associated with SEL can be caused by a variety of diseases. Disc disease, thoracic intradural extramedullary tumor like meningioma and intradural lesions, like ependymoma, astrocytoma, or a syrix were considered likely differentials prior to MRI30)
. Diagnosis is best based on MRI6,10,15)
. T1-WI differentiate epidural fat from dural content with a high degree of specificity and allow for measurement of adipose tissue thickness. Definite MRI finding of SEL is the pathognomonic appearance of fat on MRI; high signal intensity on T1-WI, intermediate signal intensity on T2-WI2,6,9,10,15)
. On CT scans, SEL presents as a homogenous hypodense epidural mass with a density between -80 and -160 HU24)
. Several grading system by MRI were reported but could not show correlation with clinical symptoms6,10,15,16,21)
. The mean sagittal thickness of the epidural fat in these studies was 4.6 mm with a normal range of 3 to 6 mm. In contrast, imaging in 6 patients with SEL revealed a mean thickness of 8 mm25)
MRI findings of our patient showed that the spinal cord was displaced anteriorly by a lipomatous tissue which was 6 mm in thickness and extended into the vertebral foramen around the DRG. We believe that the epidural fat with a 6 mm thickness was not enough to induced myelopathy.
The treatment of SEL ranges from conservative management to surgical excision. The treatment of SEL is a matter of debate, because many patients have been treated by simple weight reduction with good results7,22,24)
. However, this conservative treatment remains restricted to patients with mild neurological symptoms. Surgery is often necessary in cases wherein weight reduction failed to alleviate the symptoms or in severely symptomatic patients although the clinical suspicion for the presence of this particular neoplasia was not high4,15,19,26,28)
. A decompressive surgery with fat debulking should be considered when diet therapy proves unsuccessful or when the patient suffers acute neurological deterioration15)
. The prognosis of patients with idiopathic SEL after surgical management is favorable and no case of recurrence has been reported9)
Although our patient did not present with myelopathy, she was not able to do her usual activities and could not sleep well because of intractable chest pain which was not controlled by medications. We chose the operation for symptomatic relief and decompressed just lateral part of facet joint at symptomatic level minimally. The outcome of the operation was good and there was no recurrence for 2 years.
Whether the epidural fat shows histological alterations compared with normal fat remains unclear. Further studies should focus on the histological entity of epidural fat, given that hypervascularization and bleeding within the epidural fat could be a risk factor for symptomatic manifestation of extradural lipomatous tissue28,29,31)
. Our patient demonstrated irregular fibroadipose tissue, nodules of mature fat cells with venous engorgement on histopathological examination and no hypervascularization and bleeding. Also, we suggested that the main cause of our patient's symptom was the direct compression of the DRG by the lipomatous tissue.