Discal cysts are intraspinal, extradural cysts with a characteristic communication with the corresponding intervertebral disc level. The first identification of these lesions was a relatively recent one, with its formal description provided by Chiba et al in 2001 [1,2].

Discal cysts have only been reported in the lumbar spine region which makes it distinctive from other spinal canal cysts such as synovial cyst that usually arises either from the ligamentum flavum or the posterior longitudinal ligament in any spinal segment [3,4].

Epidemiology and natural history of this pathological entity is not settled yet, due to lack of large case series with few reported long-term follow-up. They are extremely rare among spinal pathologies and usually occur in the third or fourth decade of life. They are more prevalent in male patients with a higher occurrence reported in Asian populations.

Magnetic resonance imaging (MRI) has facilitated the diagnosis in a noninvasive manner contrary to earlier reports recommending discography as a diagnostic tool.

We report a rare case of lumbosacral discal cyst in a patient who presented to our center with a low back pain and left sided sciatic pain who underwent successful excision of the cyst via interlaminar endoscopic approach with a brief description of the operative neuroendoscopic anatomical findings with the correlated histopathological assessment.

A 31-year-old lady with the chief complaint of mechanical low back pain of 4 months duration. Initially, her symptoms were localized, infrequent and aggravated only by prolonged sitting. She sought medical advice and MRI done showed minimal disc bulges in both L4–5 and L5–S1 levels. She was managed conservatively and her back pain improved with analgesics and physiotherapy. After 5 months, she developed sciatica over her left lower limb radiating distally to the dorsum of her foot and associated with numbness of gradual onset and progressive course with poor control of symptoms with analgesics and physiotherapy. The new symptoms suggested repeating the MRI imaging that showed the progression of the degenerated disc at the level of L5–S1 to a cystic lesion.

Systemic review was unremarkable and she had no constitutional symptoms. Neurological assessment confirmed absence of any motor weakness and left straight leg raising test was positive at 60°.

MRI revealed a cystic lesion in the anterolateral epidural space with low signal intensity on T1-weighted images and high signal intensity on T2-weighted images (Figures 1 and 2).

Figures 3 and 4 showing sagittal T2-weighted and axial T1-weighted postgadolinium enhancement MRI of the lumbar spine demonstrates a spherical intraspinal, extradural cystic lesion originating from the L5–S1 disc and extending laterally to the left side and caudally behind S1 vertebral body. Noticeable is the faint peripheral enhancement around the cyst.

The patient underwent endoscopic interlaminar surgery under general anesthesia. The patient was placed in prone position with the aid of Wilsons frame, proper padding of arms and legs with caution to genitals and abdomen to be lax with no compression. Level localization was confirmed with aid of C-arm device and Karl Storz localizer aiding in both level and trajectory identification.

A 25-mm craniocaudal incision was made over the skin one finger breadth on the symptomatic side off midline. The dorsolumbar fascia was incised along the plane and widened. The underlying paraspinal muscle was then detached from the spinous process using a periosteal elevator and retracted laterally.

Application of the endoscopic system (Endospine, Karl Storz, Tuttlingen, Germany) done. The working portal was kept flush with the lamina as medial as possible. With a 45° Kerrison rongeur and curette the inferior part of the lamina and the medial part of the articular facet mass are resected to expose the ligamentum flavum.

Initial view showing indistinct anatomical structures (Figure 5) before ligamentum removal. Atypical unfamiliar view of bulging canal components.

After the incision of ligamentum flavum, the cyst was visualized clearly but the root was completely obscured (Figure 6). The sac appeared dark red in color, containing serosanginous fluid.

Before opening the sac, to make sure the root is not entailed, crossing over the top technique was used to explore the remainder of the spinal canal resulting in identification of the traversing nerve root that was encased by the sac and pushed medially and dorsally (Figure 7).

Further dissection achieved of the lateral recess to find the disc space, found the sac to be on top of disc space pushing the theca and nerve root dorsally. The cyst aspirated with fine needle and syringe yielding 1.5 mL of serous hemorrhagic fluid which was faint red in color. Then the cyst fenestrated followed by further exploration of the cavity that showed the cyst encasing fungating prolapsed disc material (Figure 8). Annulotomy performed and disc materials removed by rongeurs followed by careful dissection of the cyst wall from the nerve root and proper coagulation of the bleeding vessels.

Histopathological examination showed fragment of degenerated disc material composed of fibrohyaline tissue entangling inflammatory cells while the cyst wall lined focally by synovial lining with intervening inflammatory cells. The aspirated fluid showed a mix of red blood cells, scattered lymphocytes, oesinophilic granules and few oval cells.

The recovery was uneventful and patient was ambulating well in the same day of surgery and was discharged home. She had immediate relief of her sciatica symptoms. A week later she was reviewed, and there were neither any nerve root tension signs nor any postoperative complications except for minimal residual numbness.

The authors confirm that the procedure performed in this manuscript is in accordance with the ethical standards of the national research committee and with the 1946 Helsinki declaration and its later amendments or comparable ethical standards. Patient consent has been obtained.

DC is an extremely rare pathology with unclear pathogenesis, indeterminate natural history and still has no consensus on the ideal management.

Imaging criteria such as the MRI characteristics of the cyst, bony changes on computed tomography (CT), and contrast filling with discography can be useful to differentiate between different types of spinal cysts. DC is almost always located behind the posterior vertebral body, in close proximity to herniated discs [1]. Ganglion and synovial cysts are rather located in to the lateral aspect of the lamina and facet joint [5]. Tarlov (perineural) cysts are generally located antero-laterally within or in proximity to the neuroforamen [6,7].

On CT discography, it fills with contrast [8,9]. On CT myelogram, only Tarlov cyst fills with contrast [10]. On MRI, DC appears as hypointense on T1-weighted image and hyperintense on T2-weighted image, and enhances homogenously or peripherally after gadolinium [10]. While synovial and ganglion cysts have similar MRI characteristics to DC [11], Tarlov cyst appears as hypointense on T1-weighted image and hyperintense on T2-weighted image, with no enhancement after gadolinium [12].

An accurate understanding regarding the nature of the DC remains quite challenging due to limited literature and research in this topic. The pathogenesis and etiology of DC still remains unclear despite several proposed hypotheses. Chiba et al. [1] have proposed a preceding discal injury or disc herniation to have initiated the formation of hematoma as a result of hemorrhage of the epidural venous plexus.

On the other hand, Kono et al. [4] hypothesized that DC resulted from focal degeneration of an intervertebral disc producing a herniated disc with subsequent spilling of fluid from the herniated disc material that triggered an inflammatory response leading to reactive pseudo-membrane formation that eventually became a discal cyst. Jeong and Bendo supported the theory that the mechanism behind the formation of DC was due to a subsequent change in a herniated disc rather than a vascular phenomenon [3].

Based on our intraoperative and histological findings, we agree that the underlying pathology is due to a herniated disc with subsequent changes resulting in the formation of a DC. In addition, MRI of the case agreed with previous reports of DC that showed the cyst to be hypointense in T1 and hyperintense in T2 with close proximity to the disc space and peripheral enhancement on gadolinium study yet, it was large sized enough to be occupying half of the spinal canal diameter reaching to the facet laterally. Also, endoscopic images showed the distinguished appearance of the sac being red and filled with serosanginous material encasing an extruded disc material pushing the root dorsally and displacing the theca medially.

There are many reported lines of management of these cysts depending on the presentation and response of initial medical management yet, nearly all reported discal cysts have been treated surgically [1-4] and the majority of which underwent open surgery rather than endoscopic surgery. In our case we used the interlaminar window for endoscopic resection of that cyst that showed immediate relief of sciatica and good outcome after 1.5-year follow-up.

Endoscopic excision of discal cysts is an effective surgical option that enables successful relief of symptoms and closer inspection of the pathology and the neural structures that adds to the current knowledge of the nature of theses cysts.