Teaching Case

A 50-year-old female with a background of Marfan syndrome, blindness due to dislocation of lens and previous David procedure for ascending aortic aneurysm, presented with back pain and urinary symptoms.

Plain film imaging showed degenerative changes of the lumbar spine with posterior vertebral scalloping of the lumbo-sacral vertebral bodies [Figure 1].

Computed tomography (CT) was performed as follow up imaging for the aortic surgery, which demonstrates the posterior vertebral scalloping with widening of the right anterior sacral foramina and a fluid filled pre sacral mass [Figure 2].

Magnetic resonance imaging (MRI) of the whole spine was performed, which revealed a large anterior sacral meningocoele measuring 11cm (T) x 9cm (AP) x 9cm (CC). It extends through the right anterior sacral foramen at S2-S3 level [Figure 3]. This displaces the uterus and bladder anteriorly [Figure 4]. Dural ectasia causing scalloping of the vertebral bodies in the lumbosacral spine was also demonstrated at other levels.

Herniation of dura and arachnoid mater from the sacral spinal canal anteriorly into the pelvis leads to anterior sacral meningocoeles (ASM) [1].

Causes are multifactorial [1, 2]
• Congenital sacral or collagen defects e.g. Marfan syndrome
• Degenerative changes of the spine causing enlarged intervertebral foramen
• Traumatic injury with nerve root avulsion
• Iatrogenic injury

Congenital ASM usually occur in 1/1000 births [3, 4], with female predominance (4:1) [5, 6]. Initially asymptomatic, they can enlarge in later life presenting with pressure effects, such as back pain or sciatica, urinary incontinence and constipation [1, 5].

Patients with connective tissue disorders, such as Marfan syndrome and neurofibromatosis, have a higher incidence of ASM and associated abnormalities i.e. spina bifida and imperforate anus [5, 6]. Marfan syndrome is associated with abnormal fibrillin-1 production leading to fragmentation and disorganisation of the elastic fibres [7]. The weakened dural sac is more likely to stretch and enlarge due to hydrostatic pressures of pulsatile cerebrospinal fluid and gravity. ASM commonly occurs in the L3 to S1 region [8, 9]. As the patient ages there is enlargement of the dural sac with thinning of the pedicles and laminae, and widening of the neural foramina, leading to posterior vertebral scalloping [6].

Initial investigation by plain film radiography can demonstrate posterior vertebral scalloping or bony deformity of the sacrum, such as the scimitar sacrum where there is absence of one side of the sacrum at one or more level [6]. Further delineation of bony anatomy can be demonstrated by computed tomography (CT). However, magnetic resonance imaging (MRI) is the modality of choice providing detail of the ASM, nerve roots and complications such as tethered cord, tumours or lipomas. Sometimes, myelography can establish the communication between ASM and subarachnoid space, especially if the connection is narrow and not seen on the CT/MRI.

There is controversy between conservative or surgical management of ASM’s. Some studies suggest conservative management especially when asymptomatic, however others claim early surgical treatment is more successful with fewer complications [5, 8]. Surgery aims to obliterate the communication between ASM and subarachnoid space, releasing the nerve roots [6].

Surgical methods include:
• Open posterior approach, with sacral laminectomy to tie off the ASM neck [8].
• Open anterior transperitoneal approach usually for large ASM, with other abdominal abnormalities [8].
• Laparoscopic surgery for narrow ASM [10].
• Lumbo-peritoneal shunts are placed in patients with a high pressure ASM and surgery is unsuccessful [2].