In toto means that all of the tissue sent for pathologic examination was put on a glass slide and examined under the microscope.
A tissue sample sent to pathology needs to be placed on one or more glass slides before it can be examined by a pathologist under a microscope. The first step in this process involves deciding how much of the tissue should be put on the glass slides.
If the tissue is small enough, for example a biopsy, all the tissue can be put onto glass slides. If the tissue is very large, for example a mastectomy specimen (where the entire breast is removed and sent for pathological examination), only some parts of the tissue will be placed on glass slides.
The initial examination of a tissue sample is documented in a section of the pathology report called the gross description. This section will say if the sample was submitted in toto for microscopic examination or if only parts of the tissue sample were submitted.