As the saying goes, the pathologist is the judge, the doctor of doctors, which shows that pathology plays a pivotal role for our obstetricians and gynecologists. The following is an exposition and demystification of uterine fibroids and specific types of uterine smooth muscle tumors.
Smooth muscle tumors are a group of tumors that originate from the smooth muscle of the uterus, including uterine smooth muscle tumors, smooth muscle tumors of undetermined malignant potential, and smooth muscle sarcomas. Today, we will mainly learn about smooth muscle tumors of the uterus with you. Uterine smooth muscle tumors, divided into three categories: common (classic), histologic variant, and variant growth pattern.
This slide shows a general view of the most common type of smooth muscle tumor, the common type (classic), that we usually see in surgery: the cut surface of the tumor is grayish-white, tough and swirly.
Smooth leiomyoma is the most common benign tumor in the uterus and can be submucosal, intermuscular and subplasma.
The common common type (classic) smooth muscle tumors are generally familiar and do not pose much of a problem. There are mainly some uterine smooth muscle tumors that may have some degeneration or some special growth patterns, and these are the parts that we are more tangled with in clinical practice, so next, we will mainly introduce this aspect.
First of all, let’s introduce the changes related to the degeneration of smooth muscle tumors, which is the most common degeneration – glassy degeneration. Degeneration is actually an adaptive change of the organism, a reversible adaptation of the organism in the presence of ischemia and hypoxia. In contrast to normal smooth muscle tumors, there are no significant swirling changes visible in the cut surface, but otherwise there is no significant difference. If the area of occurrence is more extensive, it is slightly sunken compared to a classic smooth muscle tumor, similar to the feeling of scar constriction. Microscopically, this is what the picture shows. The nucleus disappears and is replaced by some uniformly red-stained, structureless material.
This is edematous degeneration, and roughly as the slide shows on the cut surface, the myxoma has a granular appearance due to interstitial edema, and occasionally nodular, as shown on the right. Then, microscopically, well differentiated spindle cells can be seen, and there is significant interstitial edema between the smooth muscle bundles, which is a benign change.
Clinically, it is commonly seen in pregnant patients and is mainly due to poor blood flow and ischemia of the leiomyoma. Metaplastic smooth muscle tumors are soft, red or dark pink, and flesh-like in appearance. Microscopic presentation: Ischemic necrosis of smooth muscle cells, in fact, we prefer to describe it as infarction.
By and large the specimen is mucousy on cut surface and microscopically more mucus secretion can be seen in the interstitium.
The above shows that multiple degenerations can occur simultaneously.
Previously, we have described degeneration caused by ischemia or elevated estrogen levels. Now we present the myxoma changes caused by medically induced factors. This figure shows a clinical treatment of uterine smooth muscle tumors with medication that results in hemorrhage and necrosis within the leiomyoma, with bleeding evident in the center of the leiomyoma.
Another clinical treatment, after ultrasound focused ablation treatment, hemorrhage and necrosis occurred in the myoma. In both of these cases, it is important to fill out a clear history when sending the pathology, otherwise the pathologist will be misled to consider the possibility of sarcoma.
Atypical uterine smooth muscle tumor, a type that sounds easily ambiguous, is essentially a benign tumor. By atypical smooth muscle tumor, we mainly mean that the tumor cells are atypical in nature, but no obvious pathological nuclear division as well as coagulative necrosis can be seen, which used to be also called pleomorphic, chimeric or syndromic smooth muscle tumor, which is a tumor with benign biological behavior.
Epithelial-like uterine smooth muscle tumor is also a subtype that is given more attention. Compared to the common type of smooth muscle tumor, its tumor cells are not spindle-shaped and have round and polygonal shape, which are morphological characteristics. It is divided into smooth myoblastoma type, clear cell type and plexiform tumor, but a small percentage of this tumor may have local infiltration, metastasis and recurrence, which is more cautious in clinical management.
In terms of microscopic presentation, in addition to atypical and epithelioid, actively dividing nuclei, cell-rich, and mucinous-like degeneration and hemorrhagic cell-rich smooth muscle tumors occasionally give rise to some ambiguity. For smooth muscle tumors with enriched nuclear schizogony, this refers to uterine leiomyomas with more abundant nuclear divisions, usually no more than 15, between 5 and 14, with only nuclear schizogony, no atypical cells, and no necrosis visible. Even in the absence of necrosis and cellular atypia, if the nuclear schwannomas are more than 15/ 10 high magnification, they cannot be classified as enriched in nuclear schwannomas and should be placed in sarcomas, smooth muscle tumors of undetermined malignant potential of the uterus.
In smooth muscle tumors, sometimes some heterologous components can be present, not only smooth muscle components, but most commonly uterine adenomyoma, with endometrial glands and mesenchyme in it, which is the most common clinically. Also, smooth muscle lipomas are more common, with a yellowish, greasy feeling on the cut surface of the myoma, and lymphocytic infiltration can be seen, even with some hematopoietic components in it.
The other is intravascular smooth muscle, which is actually intravenous smooth muscle tumor, referring to the invasion of smooth muscle tumor into the wall of venous blood vessels, which is generally manifested as intravascular Smooth muscle tumors are worm-like, tough, and grayish-white. The least common is benign metastatic smooth muscle tumor, which is defined as a uterine smooth muscle tumor, but the presence of benign smooth muscle tumor is confirmed at other sites outside the uterus, commonly in the lungs. On the right side of the figure, the top shows the HE image and the bottom is immunohistochemistry. The last one is a segmented smooth muscle tumor, which is very rare and, if it occurs, has potential communication problems between clinical and pathology. What clinically resembles a sarcoma with indistinct boundaries to the sarcoid eye and sometimes resembles a penetrating growth, is actually microscopically a nodule formed by a smooth muscle tumor bundle with an edematous, vascular-rich interstitial stroma between the nodules, which can be very stressful if such a specimen is encountered during freezing. This part of the tumor needs to be treated with caution and requires a consultation with an experienced pathologist.