Solid Omental Tumors - Symptoms, Diagnosis, and Management

Introduction

Omentum is the fatty tissue lining the abdominal organs. It hangs like a blanket in front of them. It also connects the organs to the spleen, pancreas, stomach, and colon. Various functions of the omentum are blood vessel formation, immune activity, and promoting healing in the abdominal cavity. Omentum is divided into greater and lesser omentum. The greater omentum links the colon to the stomach. On the other hand, lesser omentum attaches the liver to the stomach and duodenum. Solid omental tumor formation can occur in either greater or lesser omentum.

What Are Solid Omental Tumors?

Solid omental tumors are the tumors arising from the omentum. These tumors are extremely rare. Only 42 cases have been reported to date. However, omental metastasis is common in gastrointestinal stromal tumors (GIST) and ovarian cancers. GIST arises from the stomach and small intestine.

What Is the Cause of Solid Omental Tumors?

Solid omental tumors occur in isolated cases. The cause is not clear.

How Common Are Solid Omental Tumors?

Solid omental tumors are rare and have a gradual onset. However, some solid omental tumors are given below:

1. Liposarcoma: Liposarcoma originates from the adipose tissue. The commonly affected body areas are limbs, thighs, and abdomen. Liposarcoma of the greater omentum is rare. Only 19 cases have been reported till 2019. The average age of the patients was about 51 years in the case reports. It is more common in the body's muscles.

2. Leiomyosarcoma: Leiomyosarcoma is a rare tumor of smooth muscles.Smooth muscles are found in blood vessels, the stomach, the intestines, and the urinary bladder. About 27 cases are reported in the literature till 2016. Leiomyosarcoma of the greater omentum is uncommon. Male predisposition is found. The median age is 51 years. Due to the low occurrence of this tumor, the origin and behavior are unknown.

3. Solitary Fibrous Tumor: Solitary fibrous tumors (SFTs) are rare growths of connective tissue in the body. They are most commonly found in the lung lining (pleura). SFTs have no gender preference. They occur in the fifth to seventh decade of life. SFT was previously called hemangiopericytoma.

4. Extra Gastrointestinal Stromal Tumors: GISTs infrequently that develop outside the gastrointestinal tract are called extra gastrointestinal stromal tumors (EGIST). Omental EGISTs are rare. Around fifty-four cases have been reported to date. There was no gender preference in the cases.

5. Malignant Mesothelioma: It is a common tumor in the pleura. Peritoneal mesothelioma occurs in only 20 to 40 % of the cases (omentum is a part of the peritoneum). The cause is attributed to asbestos exposure.

Other reported primary omental tumors are fibrosarcoma, spindle cell sarcoma, leiomyoma, lipoma, myosarcoma, rhabdomyosarcoma, leiomyoblastoma, and endothelioma. These tumors arise from fat tissue, blood vessels, and lymphatic tissue.

What Is the Pathophysiology of Solid Omental Tumors?

Pathophysiology is the study of abnormal body changes. The omentum has adipose (fat) tissue with immune cell aggregates called ‘milky spots.’ This tissue acts as a cushion, filters the abdominal fluid, and protects from infection. Sorenson et al. revealed that immune and tumor cells specifically bind to these immune aggregates. In addition, omental blood vessels express the vascular endothelial growth factor receptor 3 (VEGFR3), a receptor required for angiogenesis (new blood vessel formation.) The tumor cells bind to this receptor and promote angiogenesis and tumor formation.

What Are the Signs and Symptoms of Solid Omental Tumors?

Solid omental tumors usually appear without any symptoms. However, the history may include abdominal discomfort, nausea, and weight loss. Some patients report a solid mass in the abdomen which may be painful. Other features are abdominal pain and distension, constipation, fever, and vomiting. The most frequent clinical presentation is abdominal mass and discomfort. A few patients have ascites (abdominal swelling due to fluid accumulation). Ascites and weight loss may signify malignancy. The clinical features can also appear as incidental findings on imaging.

How Are Solid Omental Tumors Diagnosed?

The physical examination reveals a solid abdominal mass that moves to one side on palpation. The mass can be palpated above or below the stomach. It sometimes involves the whole abdomen. A series of investigations is followed to arrive at the diagnosis.

1. Blood Tests: Blood investigations may reveal increased serum hormone levels. For example, liposarcoma leads to a raised serum amylase level.

2. Imaging Studies:

• Ultrasonography: Ultrasonography (USG) is a screening imaging test for an abdominal mass. It can also differentiate between solid and cystic tumors. However, it cannot localize the tumor.

• Computed Tomography: Computed tomography (CT) is used for detailed anatomy and primary tumor site identification. CT is the preferred imaging technique for greater omental tumors. The appearance is multilobulated (having several lobes) and pan-cake-like. CT and USG are also used for recurrence detection. Contrast-enhanced CT (CECT) is used for diagnosing omental leiomyosarcoma.

• Magnetic Resonance Imaging: Magnetic resonance imaging (MRI) differentiates solid from cystic tumors. It is the best modality to diagnose SFTs of the omentum.

• Positron-Emission Tomography: Positron emission tomography (PET) is combined with CT to diagnose GIST. It differentiates between benign and malignant tissues.

• Angiography: It is useful to detect increased blood supply to the tumor. A feeding artery from the omental blood supply can diagnose an omental tumor. New blood vessel channels to a tumor determine a malignant nature.

3. Immunohistochemistry: Immunohistochemistry (IHC) is a branch of science that exploits antigen-antibody reactions. IHC helps differentiate different types of omental tumors based on staining.

4. Biopsy: Although biopsy is the gold standard for confirming the diagnosis, its use is controversial. Some authors speculate that preoperative biopsy with fine needle aspiration (FNA) can contaminate the abdominal cavity.

What Is the Treatment of Solid Omental Tumors?

• The most accepted treatment of solid omental tumors is the complete surgical removal of the omentum (total omentectomy). It can be done through laparotomy. Laparotomy is the surgical incision into the abdominal cavity.

• Chemotherapy with Doxorubicin has achieved response rates of about 80 %. Hydroxyurea, Dacarbazine, and Etoposide are the other chemotherapeutic agents.

• A combination of the mentioned modalities is advocated in metastatic disease. In addition, adjuvant chemotherapy reduces recurrence chances.

• Radiotherapy is also another treatment modality. It is used in inoperable tumors. Additional radiotherapy after surgery can improve the disease outcome. Still, solid omental tumors have high recurrence rates.

The prognosis of solid omental tumors is usually poor. The median survival age of malignant omental tumors is six months. However, the prognosis also depends on the tumor stage and histology.

Conclusion

Solid omental tumors occur without symptoms with a non-specific presentation. Along with surgeons, radiologists also play a vital role in diagnosing these tumors. Studies can be performed to include the cause, progression, and newer management options. Long-term monitoring and follow-up are mandatory for the patients as frequent recurrences and metastasis can occur. More research is needed to elaborate on the progression and best treatment options for such tumors to treat them at an earlier stage.