A 52-year-old man with hypertension and diabetes mellitus undergoes elective total knee replacement under spinal anesthesia. Intraoperative course is uneventful. Two hours post-operatively, the patient develops sudden onset severe bilateral leg weakness, urinary retention, and loss of anal tone. On examination, he has saddle anesthesia and absent ankle reflexes. What is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis The patient presents with the classic triad of **cauda equina syndrome (CES)**: - Bilateral leg weakness - Urinary retention with loss of anal tone - Saddle anesthesia (perineal sensory loss) ### Timing and Mechanism **Key Point:** Cauda equina syndrome typically manifests **within hours of spinal anesthesia**, not days later. The acute onset (2 hours post-op) with bilateral motor and sphincter involvement is pathognomonic. The most common cause in the immediate post-operative period is **spinal hematoma**, particularly in patients with: - Hypertension (risk factor for vascular bleeding) - Diabetes (may have coagulopathy) - Difficult needle placement (multiple attempts → vessel trauma) ### Differential Diagnosis Table | Feature | CES (Hematoma) | TNS | Anterior Spinal Artery Syndrome | Hypotensive Ischemia | | --- | --- | --- | --- | --- | | **Onset** | Hours (acute) | 6–48 hrs | Hours to days | Intraoperative | | **Bilateral leg weakness** | Yes (severe) | Mild/burning pain | Yes (lower > upper) | Variable | | **Sphincter involvement** | Yes (hallmark) | No | Possible | Rare | | **Saddle anesthesia** | Yes | No | No | No | | **Reversibility** | Poor without urgent decompression | Self-limited | Often permanent | Depends on duration | ### Management Urgency **High-Yield:** CES is a **neurosurgical emergency**. Outcome depends on: 1. **Time to decompression** — best outcomes if surgery within 6–8 hours 2. **Severity of initial deficit** — complete paraplegia has worse prognosis 3. **Imaging** — MRI spine with contrast to confirm hematoma **Clinical Pearl:** The presence of **bilateral symptoms + sphincter dysfunction** is the red flag that separates CES from unilateral nerve root compression or TNS.