Short Bowel Syndrome (SBS)

Definition

Causes

• Acute mesenteric ischemia (arterial or venous thrombosis) - single largest event cause (75% of SBS results from a single massive resection)
• Crohn's disease - most common cumulative cause (25%, repeated resections)
• Malignancy, volvulus, radiation enteritis, trauma, internal hernia

• Necrotizing enterocolitis (NEC) - most common (~35%)
• Intestinal atresia (~25%)
• Gastroschisis (~18%)
• Midgut volvulus, malrotation (~14%)
• Sabiston Textbook of Surgery, p. 1876; Sabiston (pediatric section)

Pathophysiology

Determinants of severity

• Schwartz's Principles of Surgery, p. 1282

Site-specific consequences of resection

• Jejunal resection: Better tolerated; ileum compensates; bile salt and B12 absorption preserved
• Ileal resection (<100 cm): Bile salt malabsorption → colonic secretory diarrhea (cholerheic diarrhea)
• Ileal resection (>100 cm): Hepatic bile salt synthesis cannot compensate → fat malabsorption → steatorrhea and fat-soluble vitamin (A, D, E, K) deficiency
• Loss of the ileal brake: The GLP-1-mediated suppression of gastric emptying is lost → unabated proximal secretions, maldigestion, lack of satiety

Gastric acid hypersecretion

Intestinal adaptation

• Begins within 48 hours of resection
• Residual bowel undergoes villous hyperplasia (increased crypt cell proliferation, villous lengthening, bowel dilation and elongation)
• Continues for up to 2 years, and improvements can occur even at 3-5 years
• Driven by luminal nutrients, pancreatico-biliary secretions, and gut hormones especially GLP-2 (secreted by L cells of terminal ileum/colon)
• Other trophic factors: EGF, IGF-1, TGF-α, trefoil peptides, IL-11, growth hormone
• Goldman-Cecil Medicine, p. 994; Harrison's 22E, p. 2590

Clinical Features

• Severe, high-volume diarrhea (worst in first 3 postoperative months)
• Weight loss, malnutrition
• Dehydration and electrolyte disturbances (Na, Cl, Mg, Zn losses)
• Malabsorption: fat, protein, carbohydrate, fat-soluble vitamins
• B12 deficiency (megaloblastic anemia, neuropathy) if ileum resected
• Specific to jejunostomy patients: high-output losses of Na, Cl, HCO3, Mg, Zn, water

Long-Term Complications

• Metabolic bone disease / osteoporosis - Ca and vitamin D malabsorption; difficult to treat even with high-dose oral vitamin D
• Renal calcium oxalate stones - in patients with shortened small bowel and intact colon: Ca is saponified by malabsorbed fatty acids, freeing oxalate to be absorbed in the colon → hyperoxaluria
• Small bowel bacterial overgrowth (SIBO) - due to adhesions, abnormal motility, strictures
• TPN-associated complications - catheter sepsis, venous thrombosis, hepatic failure (leading to combined liver-small bowel transplant), renal failure, osteoporosis
• Fat-soluble vitamin deficiencies (A, D, E, K), copper, selenium, chromium deficiency
• Harrison's 22E, p. 2591

Treatment

Phase 1: Acute (immediately post-resection)

• Aggressive IV fluid/electrolyte resuscitation
• Total parenteral nutrition (TPN) - nearly always required initially
• High-dose H2 blockers or proton pump inhibitors (e.g., omeprazole 40 mg/day, lansoprazole 30 mg/day) to counter gastric hypersecretion
• Treat underlying condition

Phase 2: Adaptation (months to ~2 years)

• Gradual introduction of enteral feeding - even while on TPN, luminal nutrients are required to drive intestinal adaptation
• Anti-motility agents: loperamide (2-8 mg up to 4x/day), diphenoxylate-atropine, codeine (15-60 mg up to 4x/day), or potent opiates (tincture of opium, liquid morphine) to slow transit and maximize absorption
• Octreotide (100-250 mcg SC TID, converted to long-acting monthly if effective) for high-volume secretion (>3 L/day output) - caution: may impair intestinal adaptation in animal models
• Dietary modification:
  • With colon: low-fat, high complex carbohydrate diet; small frequent meals
  • Without colon (high jejunostomy): high-salt, nutrient-rich diet; oral rehydration solution with sodium 75-90 mmol/L
• Vitamin B12 parenterally: 500-1000 mcg IM/SC monthly
• Oral vitamin/mineral supplements at doses above standard RDA; high-potency multivitamin daily
• Magnesium supplementation: liquid preparation added to ORS, sipped throughout the day

Pharmacological: Teduglutide (GLP-2 analogue)

• Enhances intestinal mucosal growth (via IGF-1 release and direct action)
• Improves fluid absorption and intestinal/portal blood flow
• Reduces gastric secretion
• Improves intestinal barrier function

Enteral autonomy outcomes

• 50-75% of SBS patients who initially require TPN eventually achieve TPN independence
• Infants with as little as 10 cm of residual bowel have been weaned from TPN
• Adults with 35-40 cm of remaining bowel have ~50% probability of weaning from TPN; each additional centimeter increases enteral autonomy rate by ~4%
• Schwartz's Principles of Surgery, p. 1283

Surgical Options (Non-Transplant)

1. Bianchi Procedure (LILT - Longitudinal Intestinal Lengthening and Tailoring)

2. STEP (Serial Transverse Enteroplasty)

Intestinal Transplantation

1. Impending or overt liver failure
2. Thrombosis of major central veins (loss of central venous access)
3. Frequent catheter-related sepsis
4. Frequent episodes of severe dehydration

Monitoring

• Bone density (DEXA scans) - vitamin D, calcium
• Fat-soluble vitamins (A, D, E, K), B12, folate, iron, Mg, Zn
• Trace elements in TPN-dependent patients: copper, selenium, chromium
• Clinical signs: hair loss, skin/nail changes, peripheral neuropathy
• Harrison's 22E, p. 2591

Von Hippel-Lindau (VHL) Syndrome

Overview

Molecular Genetics and Pathogenesis

The VHL gene and protein

• pVHL30 - 30 kDa, 213 amino acids (full-length)
• pVHL19 - 19 kDa, lacks 53 N-terminal amino acids

Two-hit mechanism

HIF pathway (core mechanism)

1. HIF-α subunits are hydroxylated by prolyl hydroxylases
2. Hydroxylated HIF-α is recognized by pVHL, which is part of an E3 ubiquitin ligase complex
3. pVHL tags HIF-α for ubiquitin-mediated proteasomal degradation

• HIF-α subunits escape degradation, stabilize, and translocate to the nucleus
• HIF-α/HIF-β heterodimers activate hypoxia response elements (HREs) driving transcription of:
  • VEGF - angiogenesis (explains highly vascular tumors)
  • PDGF-B - tumor growth
  • TGF-α - cellular proliferation
  • Erythropoietin (EPO) - can produce paraneoplastic polycythemia
  • GLUT-1, carbonic anhydrase IX - metabolic adaptation
• Cyst formation is also explained by pVHL's role in maintaining primary cilia integrity and mediating nephron progenitor cell differentiation
• Robbins & Kumar Basic Pathology; Bradley & Daroff's Neurology; NKF Primer

VHL Disease Classification

Clinical Manifestations

1. CNS Hemangioblastomas (60-80% of patients)

• Cerebellum (~50%) - most common
• Spinal cord (especially conus medullaris, cervicomedullary junction)
• Brainstem (area postrema of medulla)
• Cerebral hemispheres (<5%)
• Retina (retinal hemangioblastoma/retinal angioma)

• Cerebellar: headache (most common), ataxia, nausea/vomiting, nystagmus
• Spinal: focal back/neck pain, sensory loss, weakness; frequently cause syringomyelia (due to intramedullary location)
• Brainstem: may cause syringobulbia
• Up to 20% have acute onset after mild head trauma

2. Retinal Hemangioblastoma (Retinal Angioma)

• May occur as early as age 1
• Peripheral lesions can be asymptomatic; central or large lesions cause vision loss
• Arteriovenous shunting → fluid extravasation
• Complications: hemorrhage, retinal detachment, glaucoma, uveitis, macular edema, sympathetic ophthalmitis

3. Renal Cell Carcinoma (RCC)

• Most common malignant tumor in VHL and leading cause of death
• Lifetime risk up to 70% (varies by mutation type)
• Clear cell histology (same as most sporadic RCCs)
• Characteristically multifocal and bilateral
• Mean age at presentation: 40 years (younger than sporadic RCC)
• Arise from proximal tubular epithelium
• Renal cysts (from distal tubular epithelium) are present in >50% of patients

4. Pheochromocytoma (7-20%)

• Often bilateral and may be extraadrenal
• Mean age: 28 years (much younger than sporadic pheo)
• Risk varies by VHL mutation type (absent in Type 1; hallmark of Type 2)
• Symptoms: episodic/sustained hypertension, severe headache, diaphoresis, flushing, palpitations; risk of hypertensive crisis, MI, stroke, heart failure
• Biochemical diagnosis: elevated plasma/urine catecholamines and metanephrines

5. Endolymphatic Sac Tumors (ELSTs) (10-15%)

• Arise from the membranous labyrinth of the inner ear
• Bilateral ELSTs are pathognomonic of VHL
• Symptoms: sudden hearing loss (from hemorrhage), tinnitus, vertigo

6. Pancreatic Lesions (5-10% for tumors; cysts are common)

• Simple serous cysts - most common, rarely cause organ dysfunction
• Serous microcystic adenomas
• Non-secretory pancreatic neuroendocrine tumors (PNETs) - usually multiple; surgery indicated when >3 cm to prevent obstructive pancreatitis
• Adenocarcinoma (rare)
• Pancreatic cysts may obstruct the bile duct or cause exocrine insufficiency when numerous

7. Epididymal and Broad Ligament Lesions

• Papillary cystadenoma of the epididymis (males) - may be bilateral; often asymptomatic but palpable
• Papillary cystadenoma of the broad ligament (females)
• Bilateral epididymal cystadenomas are virtually pathognomonic of VHL

8. Hepatic Cysts

• Common but rarely significant clinically

Diagnosis

• One characteristic VHL tumor + positive family history, OR
• Two or more characteristic VHL tumors (excluding epididymal/renal cysts alone) in a patient without family history

• Detection rate nearly 100% in patients with classic clinical features
• Recommended for: at-risk relatives with family history; sporadic cases of retinal/CNS hemangioblastoma, PCC, or ELST; clear-cell RCC diagnosed before age 50; bilateral or multifocal tumors
• (American College of Medical Genetics/National Society of Genetic Counselors guidelines)

Surveillance Protocol

• NKF Primer on Kidney Diseases, 8e

Management

CNS Hemangioblastomas

• Surgical resection is the standard treatment for symptomatic tumors
• Arteriography is not required for diagnosis but useful pre-operatively to identify feeding vessels
• Stereotactic radiosurgery is an alternative for small/surgically inaccessible lesions

Retinal Hemangioblastomas

• Laser photocoagulation or cryotherapy for small lesions
• Anti-VEGF therapy for macular involvement
• Early treatment before vision loss is key

Renal Cell Carcinoma

• Active surveillance until lesions reach 3 cm (threshold at which metastatic risk increases significantly)
• Nephron-sparing surgery (partial nephrectomy) or radiofrequency/cryoablation at the 3 cm threshold
• Total nephrectomy avoided as long as possible to preserve renal function (tumors are multifocal/bilateral)
• Tyrosine kinase inhibitors (TKIs) and anti-VEGF agents show promise in pilot studies for RCC and other lesions; further evidence needed
• A 2026 EAU Young Academic Urologists guideline (PMID: 42373875) specifically addresses kidney cancer management in VHL

Pheochromocytoma

• Alpha-blockade (phenoxybenzamine or selective alpha-1 blockers) followed by beta-blockade pre-operatively
• Laparoscopic adrenalectomy (cortical-sparing if bilateral to preserve adrenal cortex)
• Pre-operative screening for PCC is mandatory before any elective surgery in VHL patients (risk of intraoperative hypertensive crisis)

Pancreatic Tumors

• Surgery when PNETs reach >3 cm to prevent obstructive pancreatitis or malignant transformation

ELSTs

• Surgical resection when symptomatic; hearing rehabilitation as needed

Key Points Summary

• Gene: VHL on chromosome 3p25 - tumor suppressor; encodes pVHL, which targets HIF-α for ubiquitin-mediated degradation
• Core mechanism: Lost pVHL → HIF-α accumulation → VEGF/EPO/TGF-α/PDGF overexpression → highly vascular tumors
• Hallmark lesions: CNS/retinal hemangioblastomas, clear-cell RCC, pheochromocytoma, pancreatic cysts/PNETs, ELSTs
• Leading cause of death: Renal cell carcinoma (and historically CNS hemangioblastoma)
• Paraneoplastic polycythemia can occur from EPO secretion by hemangioblastoma stromal cells
• Bilateral ELSTs are pathognomonic; bilateral epididymal cystadenomas are virtually pathognomonic
• RCC management threshold: 3 cm (nephron-sparing surgery or ablation)
• PCC screening starts at age 5 (earliest onset of any VHL manifestation)
• VHL mutations are found in up to 70% of sporadic clear-cell RCCs - making the VHL/HIF pathway the central target for anti-VEGF/TKI therapy in sporadic kidney cancer as well