Naturally Occurring Biventricular Noncompaction in an Adult Domestic Cat

Figure 1. Two‐dimensional echocardiograms of the heart. (A) Right parasternal cross‐sectional LV view at the papillary muscle level shows a “moth‐eaten” appearing, hypertrabeculated, caudo‐lateral LV free wall. (B) A large, inner, noncompacted region (long arrow) appears adjacent to the thinner, external rim of normal myocardium (short arrow). P—Papillary muscle; LV—Left ventricular cavity; LVFW—Left ventricular free wall; S—Interventricular septum.

Figure 2. Right parasternal long‐axis views of the LV. (A) Large trabeculations are noted below and in front of a papillary muscle, (B) color flow Doppler echocardiogram shows that the sinusoids (recesses) created by these prominent trabeculations (noncompacted LV wall myocardium) communicate with the left ventricular chamber.

Figure 3. Necropsy specimen of the heart transected in a four‐chambered section. Upper frame shows gross features of ventricular noncompaction associated with the left ventricular free wall (defined within the box). Papillary muscle formation is indistinct. Close‐up view of the LVFW defined by the region within the box (lower frame) shows a coarse pattern of prominent, finger‐like trabeculations with deep recesses confined to the inner portion of the LV wall.

Figure 4. Histopathologic sections from the area of interest defined by the box (upper right frame, same specimen as Figure 3) demonstrate hypertrabeculated LV free wall myocardium. The inner, noncompacted portion is defined by the long trabeculae and is thicker than the outer, compacted portion of the wall. Central frame is a Masson's trichrome stain showing substantial replacement fibrosis (blue) in the papillary muscles and subendocardium and focal endocardial fibrosis affecting basal portions of sinusoids formed by excessive trabeculations. Bottom frame is hematoxylin and eosin stain. Bars are 1 mm.

Figure 5. Histopathologic section from the RV wall showing coarse and fine networks of hypertrabeculation with anastomosing, polypoid, broad, and fine trabeculae. These structures result in deep sinusoids and irregular, large spaces communicating with the RV chamber. Many small trabeculae, especially the compressed invaginations caused by intertrabecular invaginations, were not visible to the naked eye. Compared with the thick compacted inner zone in the LV, the RV compacted layer contained finer trabeculae and was relatively thin. Masson's trichrome stain.

Figure 6. Histopathologic section from the interventricular septum showing myocyte disarray. Hematoxylin and eosin stain.