Figure 3.246 Dilated lacteal pattern, clinically small bowel obstruction. Dilated lacteals (arrowheads) are most commonly caused by obstructive changes (neoplasms, adhesions, strictures, and fistulas) and radiation injury.
Lacteals are blind-ended lymphatic channels and normal constituents of the small bowel lamina propria (Fig. 3.246). Normally these delicate structures are difficult to discern at low power; on high power they appear as slightly expanded “slits” containing pale, eosinophilic serum. When dilated, the engorged structures are more readily apparent and invoke a variety of etiologic possibilities, as discussed below.
CHECKLIST: Etiologic Considerations for the Dilated Lacteal Pattern
Primary Lymphangiectasia
Secondary Lymphangiectasia
Obstruction
Adjacent Neoplasm
Adhesions
Strictures
Fistulas
Inflammatory Bowel Disease
Previous Surgeries
Infection
Whipple Disease
Radiation Injury
PRIMARY LYMPHANGIECTASIA
Primary lymphangiectasia (Waldmann disease) was first described in 1961.158 It remains a rare and poorly understood disease clinically characterized by lymph and albumin leakage into the bowel lumen, resulting in diarrhea, hypogammaglobulinemia, hypoalbuminemia, and lower limb edema. Histologically, dilated lymphatics can be seen in the mucosa or submucosa of the intestines in either a focal or diffuse distribution.159 Only a few familial cases have been reported, the majority are presumed sporadic.158 The diagnosis requires clinicopathologic correlation and, importantly, exclusion of the infinitely more common secondary forms of lymphectasia. The cornerstone of management is a life-long, low-fat diet–enriched with medium-chain triglycerides, which theoretically minimizes fatty engorgement of the “leaky” lymphatic system.160 Surgical resection is reserved for those with both localized disease and symptoms unresponsive to diet management. Additional clinical associations include malabsorption, osteomalacia (related to vitamin D deficiency), pleural effusions, iron deficiency anemia, and “yellow nail syndrome,” or dystrophic ridging of the nail with loss of the nail lunula.161 Decades of disease have been associated with B-cell lymphomas in rare cases, although the cases are too few to establish a meaningful relationship.
SECONDARY LYMPHANGIECTASIA
Identical histologic findings are seen with secondary lymphangiectasia, or lymphangiectasia secondary to some other etiology; therefore, identification of the dilated lymphatic injury pattern is only part of the diagnosis! Meticulous scrutiny of the background mucosa and thorough chart review may yield clues to the underlying etiology, the most common of which are obstructive changes (as can be seen with nearby neoplasms, adhesions, strictures, and fistulas), infections (Whipple disease), and radiation injury. Obstructive changes in the small bowel are often seen in association with dilated lymphatics, increased IELs, and a sprinkling of neutrophils in the lamina propria or epithelium. Confirmation of a history of small bowel obstruction, such as conclusive radiographic studies, intraoperative findings, or an extensive history of adhesions, strictures, or fistulas can be most satisfying when these histologic features are seen (Figs. 3.247–3.251). Unfortunately, these same findings can be seen in nonobstructed patients, who may have partial, subclinical, transient, or evolving obstruction. Difficult cases such as these require a less dogmatic approach and a careful note discussing the differential diagnostic considerations. Dilated lacteals can also be red flags to a diagnosis of radiation enteritis or Whipple disease, in the appropriate clinical setting.
Figure 3.247 Dilated lacteal pattern, clinically small bowel obstruction. In this example, dilated lacteals (arrowheads) were seen secondary to a small bowel obstruction in a patient with a history of numerous abdominal operations and extensive serosal adhesions.
Figure 3.248 Dilated lacteal pattern, clinically small bowel obstruction. At higher power, a sprinkling of intraepithelial neutrophils is seen (arrowheads), a finding not uncommon seen in small bowel obstruction.
Figure 3.249 Dilated lacteal pattern, Crohn disease. This biopsy originated from a patient with an extensive history of small bowel Crohn disease, strictures, and adhesive disease. Dilated lacteals (arrowheads) are seen in addition to gastric foveolar metaplasia (bracket), pyloric gland metaplasia, mild architectural distortion, and reactive epithelium (mucin attenuation).
Figure 3.250 Dilated lacteal pattern, radiation therapy. Radiation injury in the small bowel, similar to that in other sites, manifests as ectatic lymphovascular spaces, prominent blood vessels, lamina propria hyalinization, and stromal atypia. At this power, only scattered dilated lacteals (arrowheads) are appreciated.
Figure 3.251 Dilated lacteal pattern, radiation therapy. On higher power, the dilated lacteals (arrowheads) and haphazard blood vessels (asterisks) characteristic of radiation injury are seen. This patient had a history of radiation therapy for cholangiocarcinoma. Recognition of the radiation injury pattern is a reminder that the patient has a reasonable risk of harboring a sneaky malignancy, requiring careful examination of the background mucosa and a low threshold for ordering deeper sections.
PEARLS & PITFALLS
Occult malignancies occasionally lurk in dilated lacteals. As a result, dilated lacteals can serve as precious clues to malignancy in an otherwise busy-appearing small bowel biopsy. Make sure to routinely check all lacteals, and make sure to check them twice in those cases with a history of mass lesion or malignancy (Figs. 3.252–3.254).
Figure 3.252 Dilated lacteal pattern, metastatic alveolar rhabdomyosarcoma. In this example, the dilated lacteals harbor metastatic alveolar rhabdomyosarcoma (arrowheads) in a patient with a history of widely metastatic disease and a small bowel obstruction. The malignant cells almost blend into the normally busy-appearing duodenal mucosa (arrowhead); routine inspection of the lacteals was critical to arriving at the correct diagnosis.
Figure 3.253 Dilated lacteal pattern, metastatic alveolar rhabdomyosarcoma. A confirmatory MyoD1 was strongly positive in the indicated cells, supporting the above diagnosis.
Figure 3.254 Dilated lacteal pattern, metastatic melanoma. Melanoma, mammary carcinoma, and pancreatic adenocarcinoma are notorious for occupying dilated lacteals of the small bowel. This example features a focus of metastatic melanoma lurking in the engorged lacteal (arrowhead), underscoring the point that all lacteals should be carefully inspected for metastasis.
FAQ: Is the finding of isolated lymphectasia always clinically important (Fig. 3.255)?
Answer: No.
In a recent study of 1,866 consecutive endoscopic examinations, lymphangiectasia was clinically suspected in 3.2% and histologically confirmed in 1.9%. No clinical evidence of malabsorption was identified, even in those with subsequent biopsies showing persistent lymphangiectasia, suggesting lymphangiectasia is often an incidental or subclinical finding.162
Figure 3.255 Dilated lacteal pattern, not further specified. Dilated lacteals are routinely seen and their presence is not always clinically significant.
FAQ: What is the difference between “lymphangiectasia” and “lymphangioma”?
Lymphangiectasia refers to the dilation of indigenous lacteals in a typically flat (nonpolypoid) biopsy. In contrast, lymphangioma refers to a malformation of lymphatic vessels and is more likely to present endoscopically as a polyp, nodule or mass.
KEY FEATURES of Lymphangiectasia:
• Primary:
• Primary lymphangiectasia is a diagnosis of exclusion.
• Clinically, it is characterized by lymph and albumin leakage into the bowel lumen, resulting in diarrhea, hypogammaglobulinemia, and lower limb edema.
• Histologically, dilated lymphatics are seen in the mucosa or submucosa of the intestines in either a focal or diffuse distribution.
• Predominantly sporadic in nature.
• Treatment is a life-long low-fat diet–enriched with medium-chain triglycerides.
• Surgical management is reserved for those unresponsive to diet management with localized disease.
• Secondary:
• Histologically identical to primary lymphangiectasia.
• Common causes include obstructive changes (neoplasms, adhesions, strictures, and fistulas), radiation injury, and Whipple disease.
• Lymphangiectasia is most often an incidental or subclinical finding.