Uterine smooth muscle tumors of uncertain malignancy (USMTs) are tumors that cannot be formally classified as benign or malignant. We present a case collected in the Gynecology Department (Wing 8) of the Ibn Rochd University Hospital, Casablanca. The patient was 30 years old, married, nulligravida, with no particular pathological history. Pelvic ultrasound and MRI revealed a polymyomatous uterus with several myomas (around twenty), two of which were suspected of degeneration. Taking into account her age and gynecological status (nulligravida), the decision was made to carry out conservative treatment. The patient underwent a polymyomectomy, which ultimately resulted in a haemostasis hysterectomy with preservation of the adnexa, following uncontrollable bleeding. The anatomopathological result was in favour of uterine myomas associated with STUMP; cervix, endometrium, without signs of malignancy.
Smooth Muscle Tumors of Uncertain Malignant Potential (STUMP); Leiomyoma; Menometrorrhagia of Moderate Abundance; Leiomyosarcoma; Hysterectomy
Smooth muscle tumours of the uterus used to be classified as benign (leiomyoma) or malignant (leiomyosarcoma). Certain tumors may present unusual anatomo-pathological aspects, leading to problems of differential diagnosis, notably with leiomyosarcoma. In 2003, the WHO classified these tumours as smooth muscle tumours of uncertain malignant potential (STUMP). The diagnosis of STUMP is accepted when the smooth muscle tumor presents: true tumor necrosis, diffuse moderate to severe nuclear atypia and a mitotic index between 8 and 9 mitoses/10 HPF. It is not usually possible to diagnose STUMP before surgery and pathological examination. There is usually no further treatment after surgery, but prolonged clinical and radiological follow-up for several years.
The patient was 30 years old, married, nulligravida, with no notable pathological history, and in a period of genital activity with regular cycles. She came to us with moderate menometrorrhagia, with no other associated signs, which had been present for 4 months.
On admission, the patient was in good general condition, conscious, normotensive, normocardial, eupneic, with normocolored palpebral conjunctivae. Abdominal examination showed a distended abdomen. Gynaecological examination revealed an enlarged uterus, reaching the umbilicus on vaginal touch and abdominal palpation.
Pelvic ultrasound revealed an enlarged uterus with several myomas. In order to better determine the topography and number of myomas, a pelvic MRI was ordered (Figure 1), which revealed nodular and massed uterine myometrial lesions protruding into the endometrial cavity. The lesions were heterogeneous, with some in T2 hyper-signal; others in T2 iso-signal and T1 iso-signal. Some lesions were diffusion-restricted (Figure 2).
Figure 1: Macroscopic image of removed parts: uterus, myomas and reduced endometrial cavity.
Figure 2: Macroscopic image showing the size of the removed myomas in relation to the size of the uterus.
The case was discussed at a gynecology department staff meeting, and the decision was to perform a polymyomectomy. Haemostasis was difficult to ensure during the procedure, due to the number of myomas extirpated (over 70) and their location (isthmic, ligamentous). A haemostasis and inter-adnexal hysterectomy were therefore performed, and the specimens were sent to the pathology laboratory. It should be noted that the patient was informed of the risk of surgery, which could result in hysterectomy; hence her signature on the consent form. The patient received a total of 4 GCs (1 preoperatively to optimize her hemoglobin level and 3 postoperatively). Post-operative management was straightforward and the patient was discharged on day 3.
Anatomopathological examination revealed a histological appearance favourable to smooth muscle tumours of uncertain malignant potential (STUMP). The endometrium was proliferative. The cervix showed no signs of malignancy.
The case was rediscussed at a staff meeting of the Department of Gynecology, and the decision was made to carry out close clinico-radiological surveillance for the first year, then biannually thereafter, with an extension assessment to be scheduled.
Myomas are the most common benign smooth muscle tumours of the female genital system. However, there is a subgroup of rare and heterogeneous neoplasms that the World Health Organization has termed smooth muscle tumors of uncertain malignant potential. STUMPs are very rare tumors, and unfortunately there are no exact percentages for their incidence, certainly due to the small number of different series [1].
The clinical manifestations of STUMPs are non-specific, often similar to those of leiomyomas, namely: menometrorrhagia, abdominal distension and pelvic pain in the form of a sensation of abdominal heaviness; but also, secondary symptoms of compression phenomena or anaemia [2]. In our study, the reason for consultation was menometrorrhagia. In a study similar to ours by Cherkaoui Amal et All. the main clinical manifestation was also related to abnormal uterine bleeding (post-menopausal metrorrhagia) [3].
Preoperative diagnosis of STUMP or differentiation from leiomyoma-leiomyosarcoma with imaging modalities is not straightforward.
The MRI features of these tumors are non-specific, closely resembling those of leiomyomas and leiomyosarcomas. Tanaka et al, in a retrospective study of 24 uterine smooth muscle tumors, concluded that the presence of more than 50% T2 high signal, small T1 high signal areas and heterogeneous enhancement after PDC injection delineating areas of necrosis was suggestive of the diagnosis of STUMP and leiomyosarcoma [7].
Diffusion-weighted imaging can play an important complementary role in characterizing myometrial tumors [8, 9]. Thomassin-Naggara et al, in a retrospective study of 51 myometrial tumors, reported an overall accuracy of 92.4% in their characterization, combining T2-weighted features, high b value and ADC. Specifically, in tumors with intermediate T2-weighted signal intensity and high b1000, an ADC value below 1.23 was considered predictive of malignancy [9].
In most cases, the diagnosis is made by pathological examination. This diagnostic uncertainty frequently leads to therapeutic dilemmas. Therapeutic approaches differ from one school to another, ranging from simple myomectomy to total hysterectomy or even bilateral adnexectomy. In our case, conservative treatment by myomectomy was indicated in view of the patient's nulliparity, although the aim of the procedure was a hemostatic hysterectomy. In the case reported by Mohammed K S. et all, the patient underwent an immediate total hysterectomy + bilateral adnexectomy [5]. Recurrence rates reported in the literature range from 7% to 27%, with a total recurrence rate of 11% [6, 3]. Treatment options for recurrence in addition to surgery include adjuvant chemotherapy, radiotherapy and GnRH analogue progestins [6].
Histologically [4], three criteria are used to classify smooth muscle tumors as benign or malignant. These criteria include nuclear atypia, mitotic index and the presence of tumor necrosis. Thus, leiomyosarcomas are defined by the presence of spindle-shaped cells with: moderate to severe nuclear atypia, more than ten mitoses in ten fields at 40 X magnification, presence of tumor necrosis. Two of these criteria are necessary for a diagnosis of malignancy.
The term STUMP is used when one of the malignancy criteria is present and the second is difficult to assess. The following cases are thus classified as STUMP: a spindle-cell smooth muscle tumor with moderate to severe nuclear atypia and a borderline mitotic index of between eight and nine mitoses, a spindle-cell smooth muscle tumor with moderate to severe nuclear atypia and necrosis whose tumoral or ischemic nature is difficult to assess, a spindle-cell smooth muscle tumour with more than ten mitoses and necrosis whose tumoral or ischemic nature is difficult to assess a true tumoral necrosis in a common leiomyoma.
In our case, the anatomopathological study revealed a proliferation of spindle-shaped smooth muscle cells arranged in intersecting bundles with high cellularity, the cells presenting elongated nuclei with minimal to moderate atypia and mitosis estimated at 3 mitoses per 10 fields. Foci of coagulation necrosis were also present, some of them suspicious of malignancy (Figure 3).
Figure 3: Pelvic MRI: T2-weighted sequences in sagittal (a), coronal (b) and axial (c) sections, T1-weighted sequences in axial section (d) and diffusion-weighted sequences in axial section (e).
Globular uterus slightly laterally deviated to the right, with bumpy contours, the site of multiple nodular and mass lesions, some of which are hyposignal and others intermediate signal on T2, iso intense on T1. These lesions result in deviation of the endometrial cavity, respecting the zonal anatomy. Some lesions at the anterior corporal level are in diffusion hyper signal with low ADC.
The bladder is pushed downwards.
There is minimal effusion in the Douglas.
Figure 4: Pelvic MRI: T2-weighted sequences in sagittal (a) and (c), axial (b) and (d) sections.
Left ovary (yellow arrow) in place, multifollicular with normal appearance.
Right ovary (purple arrow) ascended in the lumbar region, seat of a simple cyst.
Figure 5: Microscopic image of a histological section after hemathein-eosin staining showing coagulation necrosis. (Red star).
STUMPs remain a difficult diagnosis due to the uncertainty between malignant and benign features. Therapeutic approaches are difficult, as to date there is no precise protocol for their management. The clinical course of the disease is unpredictable, and recurrence and metastatic risk are the hallmarks of this pathology. Consequently, patients diagnosed with STUMP will need to be monitored clinically and radiologically. We invite the medical profession to take a closer look at this pathology, and to dispel any grey areas by publishing articles and case series.
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