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plasm consists of interlacing whorl-forming bundles of long, thin spindle cells, with long but rather blunt-ended nuclei. In most areas the individual cells are loosely arranged, and generally separated from their neighbors by small clefts or a slightly granular ground substance. While in some cell bundles the component members are of similar appearance, there is great dissimilarity in other cell pockets. The cells, in general, have a thin, elongated, faintly acidophilic, smooth cytoplasm, and a long, oval nucleus containing several large chromatin particles. The nuclei vary much in size; all are prominent, some are gigantic; occasional mitotic figures are present. The neoplasm has very little supporting stroma; a broad band of collagenous fibres partly bisects the growth; outside of this coarse trabeculum only a scanty framework can be seen. The blood supply is likewise deficient; there are only a very few, small, thin-walled vessels in the sections examined. The above description answers for a second section; this has a fibrous border which the neoplasm is rather well separated. Occasional small necrotic areas are scattered through the tumor. Leiomyosarcoma (malignant leiomyoma).—B. Lucke, University of Pennsylvania Medical Schools, Department of Pathology, Philadelphia, November 25, 1924.

4. Sections were submitted personally to Dr. Ewing of New York by Dr. Feldman. Dr. Ewing's opinion was that the sections shown him presented the appearance of a malignant leiomyoma. Inasmuch as he could not find any cross-striations he would consider it a leiomyosarcoma, but if cells showing cross striations were found the tumor should be considered a rhabdomyoma or a mixed leiorhabdomyoma.

Because of this variance of opinion the growth was again submitted to Dr. Warthin for a critical discussion of the histological features presented by it. This is given, as follows:

"I am sure that this neoplasm consists largely of rhabdomyoma elements, for these

reasons:

"1. The occasional presence of long spindle or band-like cells, staining pink with eosin, and showing under the oil-immersion definite transverse striations or beadings

is one factor in deciding the nature of this neoplasm (fig. 4). From past experience I would call attention to the fact that the cross striations of rhabdomyomas show best in tissues fixed with Müller's fluid, and that they show very poorly or wholly disappear in formol-fixed preparations. In comparing sections of renal rhabdomyomas fixed in Müller's and formol we have found striations in practically every cell of the Müller's fixed tissue, and very few in the formolfixed. Even in Müller's fixed material there may be, however, numbers of cells, otherwise similar, that show no striations and may very closely resemble unstriped muscle cells, particularly when viewed by low powers (figs. 5 and 6).

“2. In addition to the occurrence of crossstriations the cells of rhabdomyoma derivation show other marked characteristics of diagnostic value. There may be a more or less poorly-defined sarcolemma. This is shown by some of the cells of this neoplasm. Further, in rhabdomyomas there are usually present band-like cells showing either segmented nuclei or separate nuclei arranged at intervals in the cell (figs. 7, 8 and 9). This neoplasm is characterized by the presence of numerous cells of this type. In rhabdomyomas there are also seen occasionally cells in which the nuclei appear to lie in pockets or depressions in the cytoplasm beneath a poorly developed sarcolemma. Such cells are also found in this neoplasm.

The dense capsule and fibrous connective tissue trabeculae, the large areas of hyaline stroma show that the growth is an old one and of very slow growth. This, with its structure and location, point to its origin in a primary developmental disturbance of the myotome. The tumor is then related genetically to the rhabdomyomatous tumors of the kidneys. While these most frequently attract clinical attention in infancy or childhood, some of them develop very slowly and become clinically important (sarcomatous) in adult years.”—A, S. Warthin, March 16, 1925.

Accepting the opinion of the rhabdomyomatous character of this neoplasm, we are dealing with a group of

tumors consisting primarily of striated muscle fibers, which although clinically considered a rarity, makes up an important part of the neoplasms of connective tissue origin. To these tumors the term "rhabdomyoma" has been applied as distinguished from "leiomyoma" the tumor of smooth muscle tissue origin.

In reviewing the literature we find that two varieties of such tumors exist: 1. The rhabdomyoma consisting of cardiac muscle.

2. Those in which the tumor consists of cells of the skeletal muscle variety.

They

The tumors classified in group 1, composed of cardiac muscle, are the rarest of the group and are considered purely as congenital anomalies. are limited to the heart, are more often found to be multiple rather than single, and are benign as they neither infiltrate nor give rise to metastasis. These tumors have for the greater part been associated with central nervous system abnormalities of which diffuse sclerosis of the cerebral cortex was amongst the chief pathological findings. Wolbach (1) has reported 12 such cases and several other cases have been recently added to the literature. Histologically these tumors are composed of two chief varieties of cells; first, there are large embryonal muscle cells with the characteristic spiderlike appearance; and second, still larger cells containing large vacuoles, nuclei, and nucleoli, together with striae which encircle the vacules and extend out to the border of the cells. Occasionally these cells are seen in teratoids and are considered as embryonic heart cells as part of the complex of tissues present.

The rhabdomyomas of the skeletal muscle type are by far the most important of this group of tumors. Having a wide range of distribution these tumors have escaped but few of the muscle regions. Two etiological factors are considered in the formation of these tumors:

1. Those arising as a direct result of irritation to a striated muscle.

2. Those arising as a result of a disturbance in development.

The first group was considered as an entity in the last century, although the tumor was recognized at a much earlier date. Ludwig Buhl (2) in 1863 reported 2 cases in adults in which rhabdomycomas followed injuries to muscle and a few cases have been reported since in which it is believed that irritation or injury to a muscle resulted in a neoplastic growth.

The second variety of tumors, due to disturbances in development is most worthy of consideration. It is a heap upon which nearly every part of the body has contributed towards its making, and as it may occur anywhere it often complicates our diagnosis and leads us to erroneous and perhaps fatal conclusions. We can not deal with the great group of disturbances in development or teratology except to say that what holds true in these tumors holds true for many of the other forms.

1. There is the simple teratoid in which the rhabdomyoma is found in any of the viscera, smooth muscle, or in striated muscle (not as the result of stimulation).

2. Complex teratomas or embryomata in which striated muscle fibers are but one part of a complex of tissues or organs in which all of the three primary germ layers are present.

As we are dealing with tumors primarily composed of striated muscle cells, we are limiting ourselves to the simple teratoid type. These tumors may be divided according to their distribution into the following groups:

1. Those in which the tumor occurs in places not normally found, viz., in the uterus or other smooth muscle organs (heterotopous).

2. Those occurring in regions in which they are normally found during the embryonic stage, but pathological in the developed fetus (heterochronous).

3. Those occurring in striped muscle but not as the result of injury or irritation.

The heterotopous tumor has been the seat of discussion as to its origin. It is believed by some that these tumors are due to misplaced anlage cells in the course of development of striated muscle, while others believe. that such may be true of tumors of the second variety (heterochronous) does not hold true for these tumors occurring in the smooth muscle regions particularly the uterus. Here they believe that the rhabdomyoma is due. to a meta plasia of smooth muscle. The latterview, although well supported, has met with opposition by Ribbert and Hauser (3) and is also somewhat opposed to our knowledge of the embryology of the muscle. Voluntary muscle, we are taught, is formed from the mesodermic somites which early differentiate into two types of cells, the more median of which surrounds the notocord and central nervous system and eventually forms the body of the vertebra (sclerotome), while the remainder of the cells form the myotome or muscle plates; smooth

muscle is derived from a condensation of a loose syncytium of mesenchyme. One of the greatest difficulties in diagnosing some of the rhabdomyomas (as was the case here) is to distinguish the types of cells one is dealing with. A rhabdomyoma may so resemble leiomyoma as to be almost impossible to distinguish them. It is for that reason that the undifferentiated cell has caused us so much difficulty in arriving at a correct histopathological diagnosis. We need but take the uterus as an example. Striped muscle cells have been described as constituents of myomas at various times, and many observers attempted to explain their presence on different grounds. Three important views held

are:

1. That the rhabdomyoma cells are the result of a metaplasia of smooth muscle tissue.

2. That it is a true rhabdomyoma, the result of misplaced anlage cells in which the undifferentiated cell resembles a leiomyoma.

3. That it is a mixed cell tumor as the result of a disturbance of both the smooth and striated muscle cells.

One can but draw his own conclusion in these cases until such times when we have a better understanding of the cause.

Although we are not dealing with rhabdomyomas of the uterus, we encountered difficulties in another path, of a somewhat different nature. Some of the most eminent pathologists disagreed on the diagnosis of rhabdomyoma, because they could not find what in their opinion was striped muscle cells but did, however, find abundant cells of the unstriped muscle type. Others clearly demonstrated

minute beading of cells very suggestive of cross striations, and therefore considered it a rhabdomyoma in which the undifferentiated cell resembled a leiomyoma. To this was added the location which favors a myotome disturbance.

Rhabdomyomas are most frequently found in the genito-urinary tract followed closely by the neck and adjoining structure. Wolfenberg (4) reports 63 cases of which 38 cases are in the genito-urinary tract. O. L. Holmes (5) reports 39 cases in the vagina of infants. Nicory (6) reported a rhabdomyoma of the uvula in a child of five. Martin and Alexander (7) re

ported a rhabdomyosarcoma of a rather rapid growth in a girl of six which recurred after the first resection.

Rhabdomyomas are usually of slow growth, but may undergo malignant changes and grow very rapidly, although as in our case there may be no evidence of any metastasis elsewhere.

In the differential diagnosis of retroperitoneal tumors the possibility of the occurrence of congenital disturbances of development in the form of inter-renal teratomas genetically related to those of the kidneys must be considered.

We are indebted to Dr. A. S. Warthin for the photomicrographs.