Causes of megacolon and megarectum

Causes of megacolon and megarectum

Primary and secondary causes ( Table 73.4 ) vary between megarectum and megacolon. The most common disease to use the term megacolon is Hirschsprung’s disease (occurring in 1 in 5000 live births) (see Chapter 17 ). Actually , in this instance, it can be argued that the so-called ‘congenital megacolon’ does in fact reflect a degree of distal obstruction from the distal contracted aganglionic segment. This leads to the absence of passage of meconium at birth and is generally incompatible with life without urgent surgery . Adult Hirschsprung’s disease is a very rare disease and leads to a megarectum because the a ff ected segment is ‘ultrashort’, a ff ecting only the transition zone of the anus. Histologically , this is very di ffi cult to diagnose with certainty and some challenge its existence at all. -

Megarectum Megacolon Figure 73.8 Schematic drawing of the distribution of bowel dilatation in megacolon and megarectum.

More common causes of megacolon include extreme senil ity and CNS neurodegenerative disease, resembling an attenu ated form of ACPO. Others are denoted ‘idiopathic’ to reflect that no cause is established; this group, who are predominantly female, phenotypically resemble a severe form of slo w-transit constipation (see Constipation ). All are rare. Patients with megarectum are usually divided into two groups by clinicians. The first are those who have had previ ous surgery for Hirsc hsprung’s disease or anorectal malforma tions in whom ongoing problems are common – due perhaps to surgical reconstruction or an as yet undetermined neuro muscular disease. The second, pr edominantly male, group are sometimes described as ‘idiopathic’; however, nearly all, if assessed carefully , will have some form of psychobeha disorder. The pathogenesis is considered to be stool withhold ing in infancy or childhood, leading to chronic distension and loss of compliance.

Megacolon Primary Congenital Classic (rectosigmoid) Hirschsprung’s disease Rare early-onset (some genetic) myopathies and neuropathies Acquired Rare late-onset (some genetic mitochondrial) myopathies and neuropathies Unknown (termed ‘idiopathic’) Secondary Genetic Muscular dystrophy and other rare genetic muscle diseases MEN type 2B with ganglioneuromatosis Rare genetic autonomic neuropathies Acquired CNS diseases, including senility, Parkinson’s, dementias, amyloid and spinal cord injury Connective tissue disease, especially scler Infections: Chagas’ disease (South American trypanosomiasis) Autonomic neuropathies secondary to diabetes and paraneoplasia Megarectum Primary Congenital Ultrashort-segment Hirschsprung’ Inadequately resected Hirschsprung’ Anorectal malformations (post reconstruction) Secondary Congenital Severe psychobehavioural + cognitive impairment (+ genetic) Acquired Later-onset behavioural (autistic spectrum) disorders Sexual abuse; neglect; parental negativism CNS, central nervous system; MEN, multiple endocrine neoplasia.