An extremely rare case of neuromuscular and vascular hamartoma of the appendix

Background Neuromuscular and vascular hamartoma is a rare lesion of the small intestine, with only 26 cases reported since its initial description in 1982. No occurrence of hamartoma in the appendix has been reported until now. Case presentation A 60-year-old man had been suffering from longstanding right lower quadrant pain. Abdominal computed tomography showed a slight swelling of the appendix as the possible cause of his pain. Laparoscopic appendectomy with partial resection of the cecum was performed for diagnostic and therapeutic purposes. An 18 × 10-mm lesion located on the tip of the appendix was found in the resected specimen. Pathological examination showed that the lesion was covered with normal mucosa and consisted of adipose tissue, smooth muscle fibers, small vessels, and neural fibers. These findings were consistent with neuromuscular and vascular hamartoma of the appendix. Conclusion This is the first report of neuromuscular and vascular hamartoma arising from the appendix.


Background
Neuromuscular and vascular hamartoma (NMVH) is a rare lesion of the small intestine, often clinically presenting as non-specific abdominal pain, recurrence of obstructive symptoms, and gastrointestinal bleeding. First described by Fernando and McGovern in 1982, this lesion consists of an aberrant proliferation of neural, muscular, and vascular elements in the small intestine [1]. Only 26 cases have been reported since its initial description, and NMVH occurred in the small intestine in all cases except one, in which it was found in the cecum [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. To our knowledge, NMVH occurring in the appendix has not been reported in the English literature until now. We report the first case of NMVH of the appendix.

Case presentation
A 60-year-old man complaining of longstanding right lower quadrant pain for 4 years was referred to our hospital for further investigation and intervention. Abdominal examination revealed spontaneous pain in the lower right abdomen without rebound tenderness or palpation of a tumor. Blood examination showed no abnormal values including tumor markers. Abdominal computed tomography (CT) identified a slight swelling of the appendix (about 10 mm) without obvious neoplastic tumors or lymphadenopathy (Fig. 1). Colonoscopy showed elevation of the mucosa around the appendiceal orifice (Fig. 2). We considered the swollen appendix to be the cause of his pain and performed a laparoscopic appendectomy with partial resection of the cecum for diagnostic and therapeutic purposes. Intraoperative findings were a slight swelling of the appendix but no tumor exposure on the serosal surface of the appendix and cecum (Fig. 3). The surgical specimen contained a submucosal lesion located on the tip of the appendix that measured 18 × 10 mm (Fig. 4). Microscopically, this lesion was covered with normal mucosa, arose from submucosa, and contained abundant adipose tissue (Fig. 5).
Smooth muscle fiber bundles, small vessels, and neural fiber bundles were collected and scattered irregularly in the submucosa, and there was no evidence of malignancy (Fig. 6). Each component of this lesion was confirmed by immunohistochemical examination. Vascular endothelium, neural fibers, and smooth muscle fibers were immunostained with CD34 ( Fig. 7a), S-100 ( Fig.  7b), and desmin ( Fig. 7c)/smooth muscle actin ( Fig. 7d) antibodies, respectively. These pathological findings were consistent with previous reports, and this lesion was diagnosed as NMVH. The patient's right lower abdominal pain disappeared immediately after surgery, and was thought to be caused by the NMVH.
The only findings in this case were longstanding right lower quadrant pain and a slight swelling of the appendix on CT imaging. As a cause of the swollen appendix without inflammation, the latency of cancer and carcinoid tumors was considered. However, we presumed that the preoperative diagnosis was less likely to be a progressive disease such as cancer because no worsening of abdominal pain or tumor formation had been observed for the 4 years since onset. For these reasons, we performed a laparoscopic appendectomy for diagnostic and therapeutic purposes. The patient's right lower abdominal pain disappeared immediately after surgery, indicating that it was likely caused by the NMVH. Although a detailed mechanism for the abdominal pain was unclear, a rise in the internal pressure of the appendix was considered as one possible cause.
NMVH has been thought to be a hamartoma that consists of an aberrant proliferation of neural, muscular, and vascular elements in the intestine [1]. However, Shepherd and Jass suggested that NMVH may represent an abnormal histologic consequence of chronic inflammatory bowel disease, especially Crohn's disease [3]. Other authors reported that NMVH might not be a rare entity but rather a process of chronic inflammation [22,23]. However, considering that most of the patients in the previous reports did not exhibit prominent fibrosis of the intestinal wall when observed in the chronic inflammatory state, it is thought that NMVH may exist as a separate entity [18]. For such reasons, the debate continues as to whether this lesion is truly a hamartoma or represents a "burnt-out" phase of various chronic pathologies.
The case presented here showed no histological features such prominent fibrosis that would indicate active or "burnt out" Crohn's disease or another reactive process induced by chronic inflammation. Therefore, we consider this NMVH of the appendix to be an entity separate from any special state of chronic inflammation.

Conclusion
We experienced a case of NMVH occurring in the appendix. Although NMVH is a benign disease, it should be included in the differential diagnosis of neoplastic lesions not only in the small intestine but also in the appendix.