A 36-year-old female patient presented to the department with muscular hypotrophy of the left leg of several months duration. Past medical history of urinary stress incontinence and the operation of a spinal lipoma. The gynaecological status was normal. No other medical complaints were reported.
X-rays of the lumbar spine and MRI without contrast enhancement are presented. The AP X-ray of the pelvis demonstrates non-fusion of the vertebral arches of L5, S1 and S2. Hemivertebra of the S3 with deformed left sacral ala is depicted. Coccygeal vertebras are not observed and their absence is confirmed on the lateral view.
On the obtained MRI images, an extradural formation at the S1-S2-S3 levels is seen, which encloses the dura. It presents with high signal intensity on T1WI and T2WI, with homogeneously suppressed signal on STIR-images. The vertebral canal is dilated caudally from L5, measuring 45/30mm at S2 level. The spinal cord reaches S1 and the central canal is subtly dilated. The terminal filum is thickened, dislocated, elongated, and reaching S1-S2 levels. Additional disc protrusion is observed at level L1-L2 without compression of the nerve roots or the dural sac.
Sacral agenesis is defined as a congenital absence of the whole sacrum or part of it. Embryologically, it is part of the group of closed spinal dysraphisms, due to disorders of notochordal formation. Approximately 15-25% of mothers of these children have insulin-dependent diabetes mellitus. It can be with autosomal dominant form of inheritance, which defines the need for genetic counselling [1]. The worldwide incidence of neural tube defects ranges between 1.0 and 10.0 per 1, 000 births, with almost half of these cases falling under the category of spinal dysraphisms [2].
Sacral agenesis has been classified into four types: types 1 and 2 refer to partial sacral agenesis, where part of the sacrum remains; types 3 and 4 refer to total absence of a sacrum, i.e. complete sacral agenesis; type 4 also involves the absence of one or more lumbar vertebrae. The defective left sacroiliac joint can be linked to a fracture, but history of trauma is required. On MRI imaging there is no oedema of bone marrow and soft tissues [3]. Early detection is important, as there is a significant association with neuropathic bladder, recurrent urinary tract infections, and incontinence.
In our case complex syndromes like VACTERL are excluded, because there is no evidence for cardiac pathology and anal stenosis. Evidence exists to suggest this can be a progressive neurological disorder due to growth and traction on abnormally positioned sacral roots, or in association with a tethered cord. Like tethered cord syndrome, diastematomyelia is a form of spina bifida occulta, but two spinal cords are clearly observed, separated by a fibrous or bony membrane in a single or double dural sac. A defect between S2 and S4 is most likely to lead to bladder dysfunction. The diagnosis is usually made prenatally and in early childhood, but mild and asymptomatic forms can be found in adulthood, as in our case. Mega sac can also lead to urinary incontinence and leg problems, but the sacrum is well-formed and only thinned. Vertebral scalloping is usually present. Clinical, neuroradiological and developmental features should be correlated when classifying spinal dysraphism [4, 5].
Sacral agenesis can be an isolated finding or it can be associated with other congenital anomalies. It can lead to clinical symptoms not only in neonates and early childhood, but in adulthood too. Early imaging is very important to start appropriate treatment and define comorbidities. As there is autosomal dominant inheritance, genetic counselling should be considered.
Sacral agenesis type I with tethered cord syndrome
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1. Pelvic, abdominal, and lumbosacral X-ray (AP and lateral views) show partial absence of the sacrum, especially with incomplete left sacral structures and developmental dysplasia or incomplete formation of the left sacroiliac joint.
2. The cortical margins of the bones are smooth, with no clear evidence of fracture lines, and no obvious signs of fresh fracture or bone marrow edema.
3. On lumbosacral MRI (T1- and T2-weighted sequences), partial absence of the posterior sacrum is observed, with no obvious abnormal bone marrow signal. The conus medullaris terminates relatively low (or shows a slightly abnormal shape), suggesting the possibility of a tethered cord or postsurgical changes.
4. No obvious evidence of a split spinal cord or bony septation is detected; no definitive signs of diastematomyelia are noted. However, further comprehensive evaluation is recommended in conjunction with the patient’s surgical history and other imaging data.
1. Partial Sacral Agenesis (Type 1 or Type 2): Based on the congenital left sacral deficiency, lumbosacral abnormalities, and a history of lipomyelomeningocele, partial sacral agenesis is highly likely.
2. Tethered Cord Syndrome: Given the patient’s previous surgical history and urinary incontinence, if there is a low-lying conus medullaris or a thickened filum terminale, the possibility of tethered cord syndrome should be considered.
3. Other Forms of Closed Spinal Dysraphism (e.g., Spina Bifida Occulta): Since the patient had a previous lipomyelomeningocele and currently shows partial sacral deficiency, other forms of closed spinal dysraphism (such as diastematomyelia) should be ruled out. However, initial imaging does not suggest typical signs.
Taking into account the patient’s age, clinical presentation (urinary incontinence, left lower leg muscle atrophy), surgical history (resection of lipomyelomeningocele), and current imaging findings, the most likely diagnosis is: “Partial Sacral Agenesis (Type 1 or Type 2) combined with possible Tethered Cord Syndrome.”
If further clarification of the degree of spinal cord tethering is needed, high-resolution MRI or neurophysiological testing can be performed, along with a comprehensive evaluation of clinical symptoms.
1. Treatment Strategy:
- Conservative Management: For patients with mild to moderate symptoms, rehabilitation training, functional exercises for the affected limb, and physical therapy can be conducted under close neurological monitoring. For urinary incontinence, pelvic floor muscle exercises and medications (such as detrusor muscle modulators) can help improve quality of life.
- Surgical Indications: If the patient shows clear signs of cord tethering (e.g., progressive neurological deterioration, pain, or decreased muscle strength), or severe cauda equina compression, surgical intervention (such as untethering or repair) may be considered. Multidisciplinary collaboration among orthopedic and neurosurgical teams is often needed.
2. Rehabilitation and Exercise Prescription (FITT-VP Principle):
- Frequency (F): Perform functional training targeting lumbosacral stability and lower limb strength 3–5 times per week.
- Intensity (I): Primarily low to moderate. Patients should feel “slight fatigue but not significant pain.” If they are in the early postoperative phase or experiencing pain, intensity should be reduced, advancing gradually.
- Time (T): 20–30 minutes per session is appropriate. Sessions may be split according to the patient’s tolerance, eventually extending to 30–45 minutes.
- Type (T): Recommend low-impact activities on the joints, such as walking on flat terrain, seated or prone leg raises, swimming, or water-based exercises. Include core stabilization exercises (e.g., simple plank variations) with appropriate load adjustment.
- Progression (P): As symptoms improve and muscle strength increases, gradually increase intensity and frequency, or incorporate balance exercises and light resistance band training. Closely monitor muscle strength, joint range of motion, and neurological symptoms, and adjust the plan as needed.
- Volume (V) & Individualization: Initial total exercise should remain within a pain-free range, gradually increasing as tolerated. Individual adjustments are necessary based on the patient’s surgical history and degree of muscle atrophy in the lower limbs.
- Precautions: Monitor bone stability and neurological function. Stop and seek medical advice if significant pain, numbness, or weakness worsens. Pelvic floor muscle training should be incorporated to help alleviate urinary incontinence.
Disclaimer: This report provides a reference based on current imaging studies and clinical information and does not substitute for in-person consultation or a formal diagnosis and treatment plan by a qualified physician. The patient should integrate clinical symptoms, laboratory tests, and specialists’ opinions when determining final treatment and rehabilitation strategies.
Sacral agenesis type I with tethered cord syndrome
