Pathophysiology of Sigmoid Achalasia
Critical Clarification
The term "sigmoid achalasia" appears to conflate two distinct pathological entities: sigmoid volvulus (a mechanical twisting of the sigmoid colon) and sigmoid-type esophageal achalasia (advanced esophageal achalasia with sigmoid-shaped esophageal deformity). These are completely separate conditions affecting different organs with different pathophysiology.
Pathophysiology of Sigmoid Volvulus
Primary Mechanical Process
Sigmoid volvulus occurs when an elongated sigmoid colon with a narrow mesenteric base undergoes axial rotation, typically counterclockwise in 70% of cases, creating a closed-loop obstruction. 1
Anatomic Predisposition
- Dolicho-sigmoid (elongated sigmoid colon on a narrow mesenteric base) is the fundamental anatomic requirement, characterized by a high and wide meso-sigmoid with a narrow root 2, 3
- Chronic constipation and frequent laxative use contribute to progressive colonic elongation over time 2, 4
Ischemic Cascade
The pathophysiology follows a predictable vicious cycle 1:
- Initial torsion → colonic distension → increased intraluminal pressure
- Decreased capillary perfusion → mural ischemia from elevated intraluminal pressure
- Meso-colic vessel occlusion → mechanical compression and axial rotation further compromise blood supply
- Early mucosal ischemia → bacterial translocation and gas production
- Progressive distension → worsening ischemia and toxic phenomena
Secondary Fibrotic Changes
- Meso-sigmoid fibrosis is observed in 86% of operated patients but represents a consequence rather than a cause of volvulus 1
- This cicatrization results from reversible ischemia in patients with relapsing forms of volvulus 1
Pathophysiology of Sigmoid-Type Esophageal Achalasia
Primary Neuromuscular Defect
Sigmoid-type achalasia represents end-stage esophageal achalasia characterized by degeneration and markedly decreased numbers of ganglion cells in Auerbach's and Meissner's plexuses, leading to failure of lower esophageal sphincter relaxation and absent primary peristalsis. 5
Progressive Structural Changes
- Chronic outflow obstruction at the lower esophageal sphincter leads to progressive esophageal dilation, tortuosity, and sigmoid-shaped deformation 6, 7
- Up to 20% of achalasia patients progress to this end-stage disease with massive esophageal dilation and dysfunctional, delicate tissue integrity 7
- The esophagus develops severe dilatation, tortuous angulation, and rotation of the esophageal body 8
Histopathologic Features
- Decreased ganglion cell numbers in Auerbach's plexus of the narrowed esophageal segment 5
- Atrophy of muscle fibers in the affected esophageal wall 5
- These changes represent irreversible neurodegeneration affecting esophageal motility 5
Management Implications Based on Pathophysiology
For Sigmoid Volvulus
Immediate surgical intervention is mandatory for patients presenting with septic shock, bowel ischemia, or perforation, as the ischemic cascade is irreversible once established. 2, 3
- For uncomplicated cases, endoscopic decompression (70-91% success rate) addresses the mechanical obstruction but does not prevent recurrence (45-71% without definitive surgery) 3
- Definitive sigmoid resection during the same admission prevents the recurrence that inevitably follows from the persistent anatomic predisposition 3
For Sigmoid-Type Esophageal Achalasia
Peroral endoscopic myotomy (POEM) with extended myotomy length (averaging 17.2 cm) is the preferred treatment for type III achalasia with sigmoid deformation, as it addresses both the lower esophageal sphincter dysfunction and the obstructive contractility of the distal esophagus. 1
- Laparoscopic Heller myotomy with Dor fundoplication remains an effective alternative, though POEM allows for longer myotomy tailored to the extent of disease 6, 9
- Clinical failure rates increase significantly over time (1.3% at 2 years, 12.8% at 5 years, 42.5% at 10 years), reflecting the progressive nature of the underlying neurodegeneration 8
- Esophagectomy may be considered for truly end-stage disease with massive dilation, though international guidelines recommend initial laparoscopic or endoscopic approaches in most patients 7