Intramedullary arachnoid cyst is one of the rare causes of slow cord compression [1],[2],[3]. The topography is most often extra- or intradural. Intramedullary location is exceptional. As a benign lesion, its etiopathogenesis is not yet well understood. It is often congenital but can also be acquired (trauma or inflammation) [4]. Its symptomatology is represented by the picture of a medullary or radicular compression. The presumptive diagnosis is obtained by magnetic resonance imaging (MRI) [5]. Surgery is the treatment of choice [1].

We report a case of arachnoid cyst successfully treated in the Department of Neurosurgery at the Grand Yoff General Hospital.

This is a 50-year-old female patient, with no previous history, admitted for back pain at T8–T9, intermittent spinal claudication with progressive reduction in walking perimeter for 15 months. The physical examination on admission showed a good general condition, a dorsal spinal syndrome, spastic paraparesis rated at 4/5, hypoesthesis under T9 sensitive territory, increased patellar and Achilles reflexes. A bilateral Babinski sign was also noted. Cutaneous abdominal reflexes were abolished at T8. There were no sensory disturbances. Anal sphincter tone was normal. The rest of the examination was unremarkable.

Spinal cord MRI revealed an intramedullary cystic formation at T8, measured 9.6 × 9.7 mm axially for a height of 29.3 mm. The lesion was hypointense on T1, hyperintense on T2, and unenhanced after injection of gadolinium (Figure 1A and Figure 1B).

The patient was operated on the day after her admission by a posterior approach with scoped tracking. She underwent a laminectomy from T7 to T9. After opening the dura mater opposite the posterior medial sulcus of the medulla, a large medulla appearance was noted (Figure 2).

A posterior medial myelotomy was performed to visualize a pearly white, translucent and avascular intramedullary mass (Figure 2). An aspiration of the cystic content associated with a partial excision of its shell was performed, thus allowing for spinal cord decompression. The cystic content was reminiscent of cerebrospinal fluid. The cyst had no communication with the subarachnoid spaces. Cytochemical analysis of the puncture fluid showed aspects of normal cerebrospinal fluid and the anatomopathological results confirmed the arachnoid cyst by showing the presence of arachnoid cells with no malignant cells (Figure 3).

The postoperative course was simple. The patient was discharged four days after the operation with full recovery of motor strength.

Intramedullary arachnoid cyst is a benign but rare condition [1],[4]. Its origin is not well known. It appears to be congenital in most cases, but it can be acquired, especially in the case of trauma and inflammation such as arachnoiditis, or even idiopathic [3],[6]. In our patient, no etiology was found. The majority of intradural cysts are located in the thoracic region (80%), which is the case for our patient, the cervical region is involved in 15% of cases and the lumbar region in 5% of cases [1].

Symptoms are related to compression of the spinal cord and nerve roots, resulting in neuralgia and neurological deficits that are usually slowly progressive due to the slow and continuous increase in volume, which is consistent with the literature [3],[7],[8]. Magnetic resonance imaging is the examination of choice for any intrarachid lesion. It allows better mapping of the lesion [3],[4]. It also allows the exact topography of the lesion, its size, extent, and relationship with the spinal cord to be determined noninvasively. The imaging appearance is that of an extraor intradural lesion, intramedullary form is exceptional; it appears hyposignal in T1, hypersignal in T2, and does not enhance on gadolinium injection [2],[8],[9]. The recommended surgical technique is to evacuate the cystic contents and to remove as much of the cystic wall as possible, leaving the portion adherent to the spinal cord in place to avoid damaging the healthy spinal cord tissue, thus allowing decompression of the spinal cord [1]. This technique was also used in our patient. The evolution was marked by regression of the initial clinical signs as reported in most cases in the literature [10].

Intramedullary arachnoid cyst is a benign and rare lesion, but it can lead to significant neurological disorders if not managed early. Our patient has been treated early which allowed a complete recovery.