Extradural arachnoid cyst in the thoracic spine: Case report

Background: Extradural arachnoid cysts (EAC) have been described as a rare cause of spinal cord and nerve root compression, usually in the mid to lower thoracic spine and at the thoraco-lumbar junction in a posterior position. The most common theory presumes a pouch-like herniation of arachnoid through a dural defect associated to subsequent pressure fluctuations in the cerebrospinal fluid during exercise and Valsalva manoeuvres can lead to distension of the cyst and symptom aggravation. Casuistic and methods: Case report based on the retrospective analysis of the medical record and complementary exams of the patient associated with a literature review of indexed databases MEDLINE, LILACS, SciElo, BIREME, Scopus, PubMED, Cochrane Library. Clinical representation: Clinical History and Neurological Examination: Male patient, 24-year-old was admitted in our service complaining of back pain seen in the thoracic topography. On clinical examination, the motor strength and deep tendon reflex in the superior and inferior limbs were normal. He presented dysesthesia in the T7 level, bilaterally. Neuroimaging Investigation: On the MRI study, there is a well presented circumscribed cystic lesion in the posterior extradural space in the t7-t8 spinal levels. The lesion showed no enhancement after the gadolinium administration. Surgery and prognostic: The patient underwent a total laminectomy centred on level T7, such that the spinal cord appeared to be completely decompressed after the cystic mass was removed. Pathological examination of the cyst wall revealed that it was composed of fibrocollagenous layers with scattered meningothelial cells, such this diagnosis of EAC was adopted. During postoperative evaluation of six months, the patient evolved well without any neurological deficits up to the present. Conclusion: Cases of EAC represents rare etiology in the spinal differential diagnosis, such that there are around only thirty cases described in the world. Although EAC is a benign pathology, the early diagnosis and adequate neurosurgical intervention aiming to complete microsurgical cyst removal and closure of the dural defect results in excellent prognosis for these patients.