Impaction is one of the most common disease of the cecum in horses. It is important to distinguish between acute and chronic recurrent cases. Acute impaction occurs suddenly and resolves within a few days with medical and/or surgical treatment whereas in chronic cases the impaction within the base or the whole cecum occurs repeatedly at irregular intervals. The chronic recurrent cecal impaction (CRCI) is characterized by hypertrophy of muscle in the cecal base or entire cecum. The pathogenesis is not fully understood: hypothesis is that the cecal impaction induces a distension during the contraction of the circular muscle layer which is a stimulus of a hypertrophy of the circular and longitudinal muscle layer in the cecum. Furthermore, neuronal density in the plexus myentericus was found to be decreased significantly in the cecal wall of CRCI. Initially, in cases of CRCI the cecocolic orifice is not entirely blocked allowing partial transit of ingesta. Hypertrophy of the muscle layer (longitudinal and circular muscle) begins at the cecal base and as the disease progresses, the cecocolic opening becomes completely obstructed due to the automatic closure mechanism. The rectal and ultrasound exam are the most useful diagnostic steps while different degrees of cecal impaction and/or tympany, a marked thickening and cecal wall contractility due to palpation are found. The hypertrophy can be regarded as a pathognomonic sign. Treatment in our study was done by surgical enlargement of the cecocolic orifice (created by Huskamp 1990). Tissue samples of defined cecal regions were taken during surgery or necropsy: the circular and longitudinal muscle layer were significantly thicker, linear neuron densities were significantly lower each compared to clinically healthy horses. Based on smooth muscle thickening and neuron deficit, rectally palpable and ultrasound visible cecal wall thickening, horses suffering from CRI have a poor prognosis. Surgery by enlargement of the cecocolic orifice in horses with CRCI have a better prognosis if only the cecal base has a thickening and a normal cecal body wall.
