2 Case Reports in Medicine (a) (b) Figure 1: MRI ﬁndings at reassessment. Cystic cavity extending from cervicocranial junction to the T4 vertebral body with myelon displacement ((a)-open arrows). A thick membrane separated the T2-hyperintense mass ((b)-triangle) from the spinal cord ((a)-long arrow). Note myelopathy signal at vertebral body heights C4/5 and disc heights C6/7 on T2-weighted (a) and T2∗-weighted images ((b)-ﬁlled arrow). muscles, and signs of bilateral chronic denervation in the upper limb which in combination with a normal cranial MRI scan was interpreted as motor neuron disease by several neurologists. In addition, a bilateral carpal tunnel syndrome was presumed on the basis of increased distal motor latencies of the median nerve. About two years later she was diag- nosed with “possible ALS” according to El Escorial criteria [2]. Neurological examination at the time of admission to our clinic (about 7 years after the ﬁrst symptoms) revealed normal cranial nerves with no signs of bulbar dysfunction and no fasciculations or weakness of facial, tongue, or neck muscles. Distinct muscle atrophy along with mild fasciculations of the upper limbs with right-sided, proximal accentuation was noted, particularly in the supraspinatus, deltoid and biceps muscles, and the ﬁnger extensors with motor strength reduced to 3-4/5. At the lower limbs, motor strength was of 4/5 of foot extensors, but no obvious atrophy or fasciculations was found. Weakness of the proximal lower limb muscles was suspected since she had diﬃculties in rising from sitting. She was able to walk independently but showed gait ataxia. Reduced vibration proprioception of all limbs and hyper- and dysesthesia of the shoulders and proximal arms were found. Deep tendon reﬂexes were symmetric, yet, extremely brisk, Babinski’s signs were absent and superﬁcial abdominal reﬂexes were retained. There were no symptoms of bladder or bowel dysfunction, but she reported neck pain and numbness and clumsiness of both arms. Proximal muscle atrophy in the arms together with sensory dysfunction and pain led anew to the suspicion of spinal pathology. Cervical MRI revealed a cyst in the dorsal intradural-extramedullary space of the cervicotho- racic region. The lesion displaced the cervical spinal cord, and myelopathy was noted (Figure 1). Myelography and postmyelography CT were conﬁrmative, and the patient was presented to the neurosurgeon. Intraoperatively, elevated pressure within the cyst was found. Cyst membranes were partially removed with fenestration of the remaining parts via a right C6/C7 hemilaminectomy. Histopathology conﬁrmed the arachnoid origin of the cyst. Postoperatively, the patient reported major relief of her neck pain and regained strength in her arms. One year later, motor and sensory dysfunctions were minimal and no acute denervation was recorded on electromyography. After stabilisation of her general condition she also recovered from depression. 3. Comment The cervicothoracic cyst in our patient had mimicked ALS symptoms as progressive amyotrophy and fasciculations along with brisk tendon reﬂexes and electrophysiological signs of acute and chronic denervation. Only one case considering a spinal cyst as a diﬀerential diagnosis to ALS has been reported: Korosue et al. [3] described a 49-year-old man with an intramedullary cyst of the conus medullaris, who presented with progressive amyotrophy of the lower limbs, clinically resembling ALS. Like our patient, this patient experienced considerable improvement after surgery. Arachnoid cysts are rare outpouchings of the arachnoid lining and may be congenital, secondary to trauma or infection, or acquired, though idiopathic [4]. To date, approximately 100 cases have been reported, with the majority (95%) occurring in the thoracic or cervical section, only exceptionally exceeding a length of three vertebral bodies [2]. MRI is the diagnostic procedure of ﬁrst choice [5, 6]. Some lesions may elude diagnosis due to the similar MRI signal of the cyst compared with adjacent subarachnoid spaces. Myelography and myelocomputed tomography may occasionally be more sensitive and provide information on CSF ﬂow dynamics [6]. In our case, neither the cystic cavity nor its membrane or mass eﬀect was detected by the ﬁrst