Lumbar disc sequestration through the dura into the intrathecal space presenting as acute cauda equina

Abstract

A 64-year-old man was referred to A&E by his general practitioner with worsening back and acute bilateral leg pain and weakness with urinary retention. His MRI scan demonstrated spinal canal stenosis at the level of L1–L2 and a diagnosis of cauda equina syndrome (CES) was made. CES is a rare neurological condition caused by compression of the central spinal nerves at the termination of the cord. CES is a surgical emergency requiring urgent assessment and treatment. The patient underwent urgent surgical decompression; however, he required a second surgery for further decompression as repeat MRI showed persistent stenosis with further extension. Intraoperative Doppler ultrasonography revealed an intradural lesion, which was surgically excised and found to be a sequestrated lumbar disc in the intrathecal space. The patient showed significant neurological improvement post revision decompression.

Background

The term cauda equina is derived from the Latin meaning of ‘horse’s tail’ which refers to the bundle of spinal nerves and nerve roots leaving the distal end of the spinal cord after its termination typically at L1. Cauda equina syndrome (CES) is a rare neurological condition caused by compression of these nerves and is a surgical emergency requiring urgent and timely decompression of the spinal cord. CES has an estimated prevalence between 1/33 000 and 1/100 000 every year.¹ CES is characterised by a myriad of symptoms, including low back pain, lower limb sensory loss, bilateral motor weakness, saddle anaesthesia, and bladder and bowel dysfunction.

There are many different causes of CES with the most common being intervertebral disc herniation (IDH) accounting for 45%; however, other causes include epidural haematoma, malignancy, trauma, spinal stenosis and post spinal anaesthesia. Intervertebral intradural lumbar disc sequestration is a rare pathology and the pathogenesis is not fully understood.² There have been documented reports in the literature; however, the majority of these cases have presented with a protracted history and tend to affect the lower lumbar spine.^{3 4} Intradural herniation accounts for only 0.26%–0.30%⁵ of all herniated disc pathology, with the most commonly affected vertebrae being L4–L5 (55%), followed by L3–L4 (16%), then L5–S1 (10%) and less commonly L1–L3.^{6 7}

CES can be subclassified further into CES-Incomplete (CES-I) and CES-Retention (CES-R). A patient with CES-I may have urinary difficulties, including altered urinary sensation; however, bladder trigone sensation is usually persevered, which can be clinically assessed by performing a catheter tug. In CES-R, the patient progresses to painless urinary retention with or without overflow incontinence, and bladder trigone sensation may be absent. This is an important distinction as it has been shown that the outcome for patients with CES-R at initial presentation are less favourable than CES-I even after decompression. According to the literature, more patients present with CES-R (50%–70%) compared with CES-I (30%–50%).¹

Intradural herniation is defined as protrusion of the nucleus pulposus through the dural layer into the intrathecal space and was first described by Dandy in 1942.⁸ Herniation of a lumbar disc is a rare complication of disc disease and represents <1% of all disc herniations though the exact mechanism of pathology is yet to be described.³

Case presentation

A 64-year-old man previously fit and well first presented to the emergency department with a 1-day history of severe back pain and acute bilateral sciatic leg pain. He underwent an MRI at the time, was reviewed by the ED team and it was felt that this was not CES. He re-presented 2 days later due to worsening symptoms with urinary retention and was referred to spinal orthopaedics and had repeat imaging. Neurological examination revealed diminished pinprick and light touch sensation below the L1 dermatome bilaterally, with the left side worse than the right and saddle anaesthesia. Motor strength was significantly weak bilaterally against resistance and absent deep tendon reflexes at the knee and ankle. Bladder ultrasonography revealed a volume in excess of 999 mL.

Investigations

At initial presentation, the patient was seen in the emergency department and his MRI was reported as ‘large central and left posterolateral disc prolapse causing significant effacement and stenosis of the spinal canal and compression of the nerve roots’. Although compression was noted, it was felt that this was not CES and the patient was discharged. On his second presentation, there was concern of cauda equina and a non-contrast MRI was reported as ‘circular stenosis at the most affected segment L1–L2 level: the large central and left posterolateral disc prolapse causing more effacement and stenosis of the spinal canal and compression of the nerve roots’ (figure 1).

Figure 1.

Preoperative axial and sagittal MRI: T2-weighted axial image at L1–L2 demonstrating a large posterolateral disc sequestration (B) through the dural layer (A) causing significant effacement with canal stenosis and compression of the nerve roots (C).

After the patient’s initial surgery, the neurology was unchanged and the patient still symptomatic of leg pain. A further MRI with contrast concluded a sequestrated disc fragment causing stenosis at this level (figure 2). The patient returned to the theatre where intraoperative ultrasonography demonstrated an intradural lesion at the L1–L2 (figure 3). Repeat MRI after the second procedure showed successful decompression (figure 4).

Figure 2.

Initial axial and sagittal postoperative MRI: T2-weighted axial image at L1/2 disc level demonstrating persistent canal stenosis due to suspected sequestered disc fragment (*), which can be seen extending inferiorly from L2 on the lateral T2-weighted sagittal view (arrow).

Figure 3.

Intraoperative ultrasonography demonstrating an intradural lesion (∆) causing compression of nerve roots (*, dura outlined by dotted line) and after removal of the fragments.

Figure 4.

Postoperative T2-weighted MRI at L1–L2 level demonstrating satisfactory decompression.

Treatment

The patient underwent emergency decompressive lumbar laminectomy and medial facetectomy. There was no intraoperative complication and a moderate amount of extremely adherent L1–L2 disc material was removed from under the dura. Immediately postoperatively, the patient’s neurology remained unchanged and was still symptomatic of leg pain. A repeat MRI demonstrated persistent stenosis, which had extended further down the posterior aspect of L2. The patient was then taken to the theatre for exploration and further inferior decompression extending to L2–L3. Intraoperatively, no extradural disc was observed. The L1–L2 disc space was further explored and washed for any remaining disc material.

Intraoperative ultrasonography demonstrated an intradural lesion at the L1–L2 extending inferiorly down the back of the L2 level. A 5 cm longitudinal incision was made in the dura at this level and revealed four sequestered disc fragments (figure 5) with the largest measuring 35 mm in length (figure 6). An annular fibrosis defect at L1–L2 was noted to open up into the intradural space. After closure of the dural sac, repeat ultrasonography did not reveal any residual intradural material.

Figure 5.

Intraoperative image of spinal cord following opening of the dural layer showing sequestrated disc.

Figure 6.

Sequestrated disc specimen removed from intrathecal space 35×15 mm.

Outcome and follow-up

Postoperatively, the patient received daily physiotherapy and occupational therapy support. The patient was reviewed by our rehabilitation medicine consultant who advised referral to Central England Rehabilitation Unit, but on assessment, was deemed to not require such high-level rehabilitation and will continue his rehabilitation at home.

Discussion

CES is caused by compression of the spinal nerves and nerve roots that arise from the terminal end of the spinal cord. CES is a rare condition and diagnosis can be difficult due to the mixed presentation of symptoms. The spinal cord commonly terminates at the level of L1 in adults. The conus medullaris is the tapered end of the spinal cord and compression at this level results in conus medullaris syndrome, which can present similarly to CES.

Approximately 5% of all accident and emergency admissions present with neurological symptoms⁹ and the vast majority of these do not present as CES. One study showed that less than 1 in 5 cases referred as CES in a 1-year period were actual CES requiring surgical intervention.¹⁰ Even though CES is rare with an estimated prevalence of 1/100 000 every year,¹ it is a very disabling condition with associated high morbidity and should, therefore, be treated as soon as possible. The British Association of Spinal Surgeons and Society of British Neurological Surgeons have produced standards of care on the management of CES. The standards state that MRI scanning should be performed as an emergency with one of four outcomes from the investigations:¹¹

• Cauda equina compression confirmed.

• Cauda equina compression excluded.

• Non-compressive pathology may be identified.

• No explanation of the patient’s symptoms may be apparent.

CES symptoms are varied, but include worsening low back pain, bilateral sciatica, bilateral lower limb neurological signs, urinary retention, bowel incontinence and saddle anaesthesia. These are listed as red flag symptoms by the National Institute for Health and Care Excellence and should prompt investigation. CES can be difficult to diagnose due to incomplete, asymmetrical or mixed pictures.¹² CES can be further subclassified depending on symptom severity, with the main determining factor being the presence of urinary retention as described by Tandon and Sankaran.¹³ CES-I includes loss of the desire to void, poor stream and strain to micturate; however, sensation of full bladder is retained. Whereas CES-R presents with painless urinary retention, overflow incontinence, no bladder sensation or control, and faecal incontinence.¹

The risk–benefit of urgent surgery is still disputed and whether timing improves or negatively impacts outcomes of CES. The majority of studies found that urgent decompression confers no benefit on outcome when CES-R is present at initial admission.^{14 15} They advocate that in cases of CES-R at presentation, they should undergo decompression on the next planned list, as operating out of hours is associated with increased complications. The limitation with these studies is often sample size due to the rarity of the disease.

Though no statistical significance has been shown in difference of outcome from symptom onset to time of surgery, a significance has been shown in outcome between those presenting with CES-R and CES-I, with better outcomes in those who are continent.¹⁶ This is important as more patients present with CES-R (50%–70%) compared with CES-I (30%–50%).¹ Therefore, if a patient presents with CES-I at initial presentation, this should be treated as an emergency regardless of time of day to confer the best possible outcomes.

As discussed previously, there is a varied aetiology of CES with disc herniation accounting for 45%. However, IDH with disc sequestration accounts for only 0.26%–0.33% of all herniated disc pathology; however, one study showed it to be as high as 1%.¹⁷ The most common affected vertebral level with disc sequestration is L4–L5 (55%) followed by L3–L4 (16%) then L5–S1 (10%) and least common higher lumbar L1–L2 and L2–L3 levels.^{6 7} Our case is about a man who was found to have an L1–L2 intradural herniation with disc sequestration resulting in CES, which is a very rare pathology.

The exact pathogenesis is unknown, though one widely accepted theory is that a weakness in the posterior longitudinal ligament allows adhesions between the annulus fibrosus and the anterior aspect of the dura. This can promote a path for the disc to herniate through.

Until now, there have been nine reported cases in the literature involving IDH at L1–L2,⁵ with the most recent reported by Low et al.¹⁸ In total, two other reports demonstrated CES-R similar to our case, this was described by Ponzo et al ⁵ and Smith.¹⁹ However, unlike our patient, both these other patients had a long preceding history of back pain. Papers reporting IDH at L1–L2 are summarised in table 1. There are other reports of IDH at the other levels L2–L3,²⁰ L3–L4,²¹ L4–L5^22–25 and L5–S1;²⁶ however, it is documented that lesions at other levels are more common unlike with our rare presentation.

Table 1.

Summary table of other reported L1–L2 intradural disc herniations

Paper	Patient	Symptoms	Treatment
Arnold and Wakwaya (2011)27	63 F	Paraparesis	Posterior fusion
Arnold and Wakwaya (2011)27	69 F	Back pain, thigh pain	Laminectomy
Ponzo et al (2020)5	65 F	Back pain, bilateral sciatica, urinary retention	Laminectomy
Aprigio et al (2019)28	57 M	Back pain, thigh pain	Microdiscectomy
Ozturk et al (2007)29	50 F	Back pain, paraparesis, bilateral sciatica	Laminectomy
Low et al (2020)18	74 F	Back pain, intermittent claudication	Lumbar exploration
Koc et al (2001)30	65 M	Back pain, paraparesis, urinary incontinence	Laminectomy
Carvi et al (2007)31	56 F	Back pain, incomplete paraparesis	Hemilaminectomy
Smith (1981)19	66 M	Back pain, paraparesis, urinary retention	Laminectomy

F, female; M, male.

Radiological appearances are not always conclusive and preoperative diagnosis can be difficult in cases of intradural disc herniation. It is due to the rare and complex nature that difficulty with preoperative imaging and diagnosis can result in delayed treatment. On review, it was felt that this case should have been referred on initial presentation, a duty of candour discussion was held with the patient regarding this. MRI still remains the imaging modality of choice and some papers have reported a ‘hawk beak’ or ‘hawksbill’ sign. This is characterised by a beak-like shaped ring or annulus enhancement in the intervertebral space on T2-weighted MRI imaging.⁵

In conclusion, IDH is a very rare complication of disc pathology occurring in as low as 0.3% of cases and is even more uncommon at the level of L1–L2. CES-R has now only been reported three times to our knowledge and is a serious condition that carries a high associated morbidity, which can have irreversible effects on patient’s quality of life. The unique feature we present with our case compared with other case reports is the rapid onset of symptoms in the absence of a preceding history, which culminated in severe CES-R. In our case, the patient underwent an emergency decompressive lumbar laminectomy and medial facetectomy, and although there was a moderate amount of L1–L2 disc material, his neurology did not improve. A repeat MRI demonstrated persistent stenosis, which resulted in a second surgical exploration and further inferior decompression. Intraoperative ultrasonography demonstrated an intradural lesion at the L1–L2, extending inferiorly down the back of the L2 level, which was excised. Our patient has already shown some improvement in neurology and is continuing his rehabilitation.

Patient’s perspective.

The week before I was walking about fairly normally taking our dog for two walks a day. I do also suffer with an ongoing foot problem, but otherwise fairly active. One day, I started to feel very tight in my back and bending down to put my shoes on was quite painful and having trouble to stand all of a sudden. By the next day, I was having a job to stand; there was a lot of pain in my legs and back, shooting up and down.

That day I went to accident and emergency (A&E) and was examined and had an MRI scan and was later discharged with no real explanation or any medication. Two days later, my condition had got considerably worse. I had an appointment at my doctor, where I was referred straight back to A&E with a letter from my doctor. My son and wife struggled to get me in and out of the car, but eventually arrived back at A&E. I went through similar treatment and another MRI scan, after which I was admitted and told I needed an operation on my spine. By this time, I could not feel my left leg and very little in my right leg, and any movement was extremely painful, even when slid from bed to bed and was transferred to a ward.

I felt frightened, but the nursing staff were great and reassuring to me. The day of the operation, I still could not believe how my life had gone downhill so fast. All the risks of the operation were explained to me and I was taken down to theatre. All went well and when I woke up, I didn’t feel too bad. I still had no feeling in my legs, especially the left. Later that day, I was sent for another MRI. This one I’m sure was twice as long as the previous two scans. The next day, I had a second operation as some of the disc from my lower back had become embedded in the nerve sac, which apparently doesn’t happen very often. Guess that’s me, just have to be different! Coming round from my operation, it seemed to have taken a lot more out of me. I felt extremely tired, and at that time, I was far from being positive in my mind about anything.

Two days later, working with the physios, I tried to stand in a round frame, I found this extremely painful, but I was holding myself too tense. I managed to sit in a chair for a while, which felt good. After a week, the pain seemed to ease, but I still felt stiff, with little feeling in my left leg. Next, I started to use an atlas frame, which helped a lot getting me up, and after a while, I could slowly move around the ward. My confidence was coming back. A few days later, I was using a Zimmer frame. The next day was much better; I made it to the toilet and back to the ward. The feeling is slowly coming back in my left leg, but I still struggle to lift my leg. I have now started to use only crutches and continue with making good progress.

Though I think my recovery will be fairly long, but compared with 4 weeks ago, I feel much better, mentally and physically. All my thanks again to my consultant and his team and everybody who has helped me in hospital.

Learning points.

• Cauda equina syndrome (CES) is a rare neurological condition that can present with an array of symptoms and this was a classical presentation of CES with retention.

• CES due to disc sequestration through the dural sac is a rare aetiology and even more so at higher lumbar level as in this case.

• Patients response to initial surgical treatment should be scrutinised if not showing the improvement expected; this should be investigated further due to seriousness of the condition. In this case, not repeating the MRI on the same day post first decompression could have led to delay in treatment.

• Use multiple imaging modalities to gain full picture, without intraoperative ultrasound, would not have located the intradural lesion, which was excised and found to be a sequestrated disc.